WO2019115614A1

WO2019115614A1 - Peptidic melanocortin 1 receptor agonist - saccharide functionalised carbaborane conjugates

Info

Publication number: WO2019115614A1
Application number: PCT/EP2018/084563
Authority: WO
Inventors: Annette Beck-Sickinger; Sylvia ELS-HEINDL; Philipp Wolf; Evamarie Hey-Hawkins; Martin KELLERT; Robert KUHNERT; Stefan SARETZ; Bernd Riedl; Donald Bierer; Johannes Koebberling; Nils Griebenow
Original assignee: Universität Leipzig
Priority date: 2017-12-12
Filing date: 2018-12-12
Publication date: 2019-06-20

Abstract

The present invention covers peptidic melanocortin 1 receptor agonist –saccharide functionalised carbaborane conjugatecompoundsof general formula (I), in which R¹, X¹, X², L-His, X³, L-Arg, X⁴, X⁵, r, and CbD are as described and defined herein, methods of preparing said compounds, intermediate compounds useful for preparing said compounds, pharmaceutical compositions and combinations comprising said compounds, and the use of said compounds for manufacturing pharmaceutical compositions for the treatment of cancer by means of boron neutron capture therapy.

Description

PEPTIDIC MELANOCORTIN 1 RECEPTOR AGONIST - SACCHARIDE FUNCTIONALISED

CARBABORANE CONJUGATES

The present invention covers peptidic melanocortin 1 receptor agonist - saccharide functionalised carbaborane conjugate compounds of general formula (I) as described and defined herein, methods of preparing said compounds, intermediate compounds useful for preparing said compounds, pharmaceutical compositions and combinations comprising said compounds, and the use of said compounds for manufacturing pharmaceutical compositions for the treatment of cancer by means of boron neutron capture therapy.

BACKGROUND

The present invention covers peptidic melanocortin 1 receptor agonist - saccharide functionalised carbaborane conjugate compounds of general formula (I) which, by selectively targeting the melanocortin 1 receptor, accumulate in tumour cells and allow for the treatment of cancer by means of boron neutron capture therapy.

Despite advances in medicine, there is a multitude of deadly diseases, e.g. cancer. A novel therapeutic approach is boron neutron capture therapy (BNCT). For this binary method, ¹⁰B is selectively accumulated in cancer cells, which are subsequently irradiated with low energy neutrons with approximately 0.025 eV [Barth et al., Cancer 1992, 70, 2995-3007] The capture of these neutrons by ¹⁰B results in excited ¹¹B nuclides that undergo nuclear fission releasing the high linear energy transfer (LET) particles ⁴He and ⁷Li. These LET particles cause cell cycle arrest and apoptosis by DNA fragmentation in the host cell due to their effective range of 6 - 9 nm [Garabalino et al., Appl. Radiat. Isot. 2014, 88, 64-68; Faiao-Flores et al., Toxicol. In Vitro 2013, 27, 1196-1204] In addition, emitted g-rays ionize intracellular compartments leading to loss of function and further decreased cell survival rates [Keta et al., Appl. Radiat. Isot. 2014, 10, 578-586]

An interesting target for BNCT is malignant melanoma, which is caused by endogenous factors like genetic instability and exogenous factors as UV radiation [Erdei et al., Expert Rev. Anticancer Ther. 2010, 10, 181 1-1823] Spreading to other tissues via infiltration of the blood or lymphatic system is the main reason for the deadliness of malignant melanoma, which is responsible for over 10,000 deaths every year solely in the United States [Finn et al., BMC Med. 2012, 10, 1-23]. Additionally, a worldwide increasing incidence rate for melanomas is observable [Parkin et al., Int. J. Cancer 2001 , 94, 153-156]. Treating melanoma is difficult due to early metastasis and resistance of the disseminated cells towards state of the art therapies like aggressive removal of cancerous tissue, radiotherapy and chemotherapy (e.g. with the FDA- approved dacarbazine) [Braeuer et al., Pigment Cell Melanoma Res. 2014, 27, 19-36; Bhatia et al., Oncology 2009, 23, 488-496]. Owing to that, patients suffering from malignant melanoma have a 5-year survival rate less than 5 %, which decreases drastically after the onset of metastasis [Buzaid et a!., J. Clin. Oncol. 2001 , 19, 3635-3648; Houghton and Polsky, Cancer Cell 2002, 2, 275-278]

For the selective accumulation of sufficient ¹⁰B in cancerous cells, a cell-targeting compound with high boron loading is needed. Until today, only two different boron containing molecules are under intensive investigation: boronophenylalanine (4-dihydroxyborylphenylalanine, BPA) and sodium borocaptate (disodium undecahydro-mercapto-c/oso-dodecacarborate(12), BSH). However, both compounds are not ideal BNCT agents as BPA is not a selective cell-targeting compound and BSH lacks selective cellular uptake mechanisms, leading to possible off-target effects [Morita et al., Cancer Res. 2006, 66, 3747-3753, Soloway et al., Chem. Rev. 1998, 98, 1515-1562; Crivello et al., J. Biol. Inorg. Chem. 2009, 14, 883-890].

The use of peptide-drug conjugates can overcome these disadvantages. The peptide should target a receptor that is specifically overexpressed in the cancerous tissue. In case of melanoma, the melanocortin 1 receptor (MCiR) can be addressed as it is present in malignant cells and metastases [Salazar-Onfray etal., Br. J. Cancer 2002, 87, 414-422] The octapeptide NAPamide is a synthetic, shortened and modified derivative of the endogenous MCiR ligand a-MSH (a melanocyte stimulating hormone) [Sahm et al., Peptides 1994, 1515, 441 -446] The sequence contains the His-Phe-Arg-Trp motif necessary for MCiR binding and activation as well as the non-proteinogenic amino acids L-norleucine and D-phenylalanine. Compared to other a-MSH analogs, NAPamide contains L-glycine at the C-terminal peptide region, which was shown to increase the potency at the MCiR, and is known to be modifiable at position Lys⁸ without interference with the peptide-receptor interaction, allowing the introduction of boron loaded compounds [Froidevaux et al., J. Nucl. Med. 2004, 45, 1 16-123] Here, compounds with high boron loading can be introduced. Carbaboranes are physiologically stable, hydrophobic and icosahedral carbon containing boron clusters (molecular formula: C2B10H12), with boron carrier potential [reviewed in Lesnikowski, J. Med. Chem. 2016, 59, 7738-7758] With peptide- carbaborane-conjugates, it is possible to exceed the necessary amount of boron needed for BNCT (10⁹ atoms per cell), which could be shown by high uptake in in vitro test systems for receptors overexpressed in breast cancer cells [Ahrens et al., ChemMedChem 2015, 10, 164- 172] These results are a promising basis for the successful establishment of BNCT for malignant melanoma. Thus, NAPamide-carbaborane-conjugates are highly interesting as a melanoma- selective shuttle system for BNCT. Prior art

The application of boron neutron capture therapy (BNCT) is currently still limited due to the low number of boron-based compounds available (see e.g.\ Luderer et al., Pharm. Res., 2015, 32, 2824-2836; Savolainen et ai, Physica Medica 2013, 29, 233-248; Yamamoto et ai, Transi Cancer Res. 2013, 2, 80-86).

The concept of selective targeting of receptor expressed on cell surfaces with their corresponding c/oso-(carba)borane-modified peptide ligands as potential approach for BNCT has been reported before (Schirrmacher et ai, Tetrahedron Lett. 2003, 44, 9143-9145; Mier et ai, Z. anorg. allg. Chem. 2004, 630, 1258-1262; Betzel et ai, Bioconjugate Chem. 2008, 19, 1796-1802).

Carboxylic acid derivatives (for conjugation with peptides) and sugar derivatives (for improved solubility) of carbaboranes have been disclosed in scientific publications see e.g. Ahrens et ai, ChemMedChem 2015, 10, 164-172 (for the facilitated introduction of a carboxylate moiety), Frank et ai, Polyhedron 2012, 39, 9-13 (for a carboxylic acid synthon featuring three carbaborane moieties per molecule), Frank et ai, J. Organomet. Chem. 2015, 798, 46-50 (for deoxygalactosyl-functionalised carbaborane synthons).

The Beck-Sickinger group already reported the promising approach of selectively targeting breast cancer cells via NPY1 receptor-targeted orf/70-carbaborane-neuropeptide Y conjugates (Ahrens et ai, J. Med. Chem. 2011 , 54, 2368-2377; Ahrens et ai, ChemMedChem 2015, 10, 164-172).

A poster presented on a scientific conference (D. J. Worm et al., 25^th American Peptide Symposium, 17 - 22 June 2017) discloses carbaborane-[F⁷,P³⁴]- peptide conjugates featuring carbaboranes modified with a hydrophilic moiety and a branching unit, with a carbaborane loading of up to six carbaboranes per [F⁷,P³⁴]-NPY peptide, which were shown to be capable of activating the Yi receptor, and of effecting internalization of the Yi receptor tagged with an eYFP fluorophore into HEK 293 cells.

It is further known that the uptake of carbaborane glycosides into tumour cells strongly depends on the specific structure of the respective carbaborane glycoside (Tietze et al., ChemBioChem 2001 , 2, 326-334). Interestingly, the same group discussed the suitability of monosaccharide carbaborane glycosides based on water solubility considerations in context of BNCT, resulting in the preparation of disaccharide carbaborane glycosides and their subjection to cancer cell toxicity studies (Tietze and Bothe, Chem. Eur. J. 1998, 4, 1 179-1183). Therefore, ready uptake of saccharide functionalised carbaborane conjugate into tumour cells as a merit of the saccharide conjugation per se cannot be expected. The melanocortin 1 receptor, belonging to the melanocortin system, is overexpressed on the cell sufarce of melanoma cells and can be addressed with the synthetic ligand NAPamide (Froidevaux et ai, J. Nucl. Med. 2004, 45, 1 16-123).

However, the state of the art does not describe the peptidic melanocortin 1 receptor agonist - saccharide functionalised carbaborane conjugates of general formula (I) of the present invention as described and defined herein.

It has now been found, and this constitutes the basis of the present invention, that the compounds of the present invention have surprising and advantageous properties.

In particular, the compounds of the present invention have surprisingly been found to effectively mediate activation of the human melanocortin 1 receptor, resulting in internalization of the receptor, together with the compounds of the present invention bonded to it, into HEK293 cells transfected with the human melanocortin 1 receptor, for which data are given in biological experimental section, and can therefore be used to selectively transport boron atoms into cells expressing the melanocortin 1 receptor, such as melanoma cells, to enable boron neutron capture therapy of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma. Furthermore surprising, high levels of receptor activation and internalization are maintained over a range of carbaborane loading, up to at least four carbaborane units per peptide unit, enabling for transferring a large number of boron atoms per cell into cells expressing the human melanocortin 1 receptor. So far, multiple carbaborane loading to receptor activating peptides has been known hitherto only for a completely different type of receptor, i.e. the human Yi receptor, to be compatible with high levels of receptor activation and internalisation.

DESCRIPTION of the INVENTION

In accordance with a first aspect, the present invention covers compounds of general formula (I):

in which :

R¹ represents a group R²-C(=0)-, in which R² represents a group selected from Ci-C₆-alkyl, phenyl-Ci-C3-alkyl-, and phenyl, in which the phenyl group and the phenyl present in phenyl-Ci-C3-alkyl- are optionally substituted, one, two or three times, identically or differently, with a group selected from a halogen atom, Ci-C3-alkyl, and Ci-C3-alkoxy, X¹ represents an amino acid selected from L-norleucine, D-norleucine, norleucine as isomeric mixture, L-methionine, D-methionine, and methionine as isomeric mixture,

X² represents an amino acid selected from L-alanine, D-alanine, alanine as isomeric mixture, L-glutamic acid, D-glutamic acid, glutamic acid as isomeric mixture, L-aspartic acid, D-aspartic acid, aspartic acid as isomeric mixture, L-serine, D-serine, and serine as isomeric mixture,

L-His represents L-histidine,

X³ represents an amino acid selected from D-phenylalanine, L-phenylalanine, and phenylalanine as isomeric mixture,

L-Arg represents L-arginine,

X⁴ represents an amino acid selected from L-tryptophan, D-tryptophan, and tryptophan as isomeric mixture,

X⁵ represents an amino acid selected from glycine, L-alanine, D-alanine, and alanine as isomeric mixture,

represents an integer selected from 0, 1 , 2, 3 and 4, CbD represents a group selected from

Cb-$,

which

q, in each instance it occurs, independently from each other represents an integer selected from 1 , 2, 3 and 4,

$ represents the point of attachment to the rest of the molecule,

Cb represents a group

Sac

Sac represents a group selected from

and

represents a boron atom which is bonded to a hydrogen atom in addition to the bonds shown within the group Cb, and

“o” represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group

Cb,

and isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, and mixtures of same.

DEFINITIONS

Tables 1a, 1 b, 1c, 1d, and 1e: Nomenclature of amino acids, peptide sequences, and carbaboranes

Table 1a: Nomenclature of amino acids and peptide sequences

Table 1 b: Nomenclature of non-proteinogenic amino acids:

Diaminoalkanoic acid based branching moieties of the structure shown below, in which q is as defined for the compounds of the general formula (I), are also being referred to herein as DAABM.

DAABM

Table 1c: Side chain protected amino acids:

The term“side chain protected amino acid”, as used herein, refers to an amino acid featuring a protecting group, herein also referred to as PG¹, PG², PG³, PG⁴, PG⁵, or PG⁶, or shown specifically, attached to a functional group on a side chain of said amino acid. Abbreviations used for said protecting groups are defined by chemical name in table 3, below, or abbreviations are used as known to the person skilled in the art. Unless specified otherwise, said side chain protected amino acids are presented as three-letter-codes, including the stereochemical terminology as discussed below. Further, the term “side chain protected amino acid” encompasses said amino acids as part of a peptide sequence, which is optionally bonded to a resin, such as an amide resin, or in free form, optionally featuring additional protecting groups at the C- and/or N-terminus. Specific examples are presented in table 1c.

 Carbaboranes

Carboranes (“carbaboranes” in the formal nomenclature, and as used herein) are polyhedral boron-carbon molecular clusters that are stabilised by electron-delocalised covalent bonding in the skeletal framework. In contrast to classical organoboranes such as borabenzene (C₅H₅B), the skeletal carbon atoms in carboranes typically have at least three and as many as five or six neighbours in the cluster, forming stable - in some cases, exceedingly stable - molecular structures. In late 1957, an extraordinarily stable compound characterised as BioHioC₂H₂ (later given the trivial name o-carborane, 1 ,2-C₂BioHi₂), has been isolated at Reation Motors, Inc. from the reaction of B₁₀H₁₄ derivatives with acetylene. The original work in the icosahedral C₂B₁₀H₁₂ carboranes was published in 1963 in a series of papers from the groups at Thiokol and Olin- Mathieson. The two remaining isomers, 1 ,7- and 1 ,12-C₂BioHi₂ (m- and p-carborane, respectively) were prepared via thermal cage-rearrangement of o-carborane. Investigations of the C₂B₁₀H₁₂ systems revealed that their cage C-H bonds are highly polar (especially in the 1 ,2- and 1 ,7-isomers, and to a lesser degree in the 1 ,12-isomer), imparting a positive charge on the CH hydrogens and making them acidic toward Lewis bases. (Russel and Grimes, Carboranes, 2016, 3^rd Ed., Elsevier Inc., page 1 ). In the carbaboranes shown in the structural formulae herein, a symbol“·” represents a boron atom which is bonded to a hydrogen atom in addition to the bonds shown within the respective group or formula, and a symbol“o” represents a boron atom which is bonded as shown to but not further bonded to hydrogen atoms not shown explicitly.

Table 1d: Nomenclature of the different carbaborane synthons:

Table 1e: Nomenclature of the different carbaborane moieties:

The term“resin” in general means an insoluble polymer, also called solid support, which is functionalized for solid phase peptide synthesis, wherein the C-terminal amino acid of a peptide is attached to the resin covalently and the full peptide is cleaved from the resin after completion of the synthesis. As used herein, the term“amide resin” means a resin from which upon cleavage a peptide featuring a C-terminal carboxamide is released. This is usually achieved by using a linker which is covalently attached to the resin and provides a reversible amide linkage between the synthetic peptide and the solid support. Amide resins, and said linkers contained therein, are known to the person skilled in the art and are described in the literature (see e.g. Fmoc Solid Phase Peptide Synthesis - A Practical Approach, edited by W. C. Chan and P. D. White, Oxford University Press, 2000, ISBN 0-19-963724-5). Amide resins, as referred to herein, are exemplified by but not limited to a Rink amide AM resin (commercially available from Iris Biotech) or a NovaSyn® TGR R resin (commercially available from Novabiochem, Darmstadt, Germany).

The term "peptide" as used herein, refers broadly to a sequence of two or more amino acids joined together by peptide bonds. It should be understood that this term does not indicate a specific length of a polymer of amino acids, nor is it intended to imply or distinguish whether the polypeptide is produced using recombinant techniques, chemical or enzymatic synthesis, or is naturally occurring.

The term“conjugate”, as used herein, refers to a peptide as described and disclosed herein, to which at least one carbaborane moiety is attached.

The term "amino acid" or "any amino acid" as used herein refers to any and all amino acids, including naturally occurring amino acids (e.g., oL-amino acids), unnatural amino acids, modified amino acids, and non-natural amino acids. Natural amino acids include those found in nature, such as, e.g., the 23 amino acids that combine into peptide chains to form the building- blocks of a vast array of proteins. These are primarily L stereoisomers, although a few D-amino acids occur in bacterial envelopes and some antibiotics. Those of the 20 proteinogenic, natural amino acids of relevance for the present invention are listed in the above table 1 a. The "non- standard," natural amino acids are pyrrolysine (found in methanogenic organisms and other eukaryotes), selenocysteine (present in many non-eukaryotes as well as most eukaryotes), and N-formylmethionine (encoded by the start codon AUG in bacteria, mitochondria and chloroplasts). "Unnatural" or "non-natural" amino acids are non-proteinogenic amino acids (/^'.e., those not naturally encoded or found in the genetic code) that either occur naturally or are chemically synthesized. Over 140 natural amino acids are known and thousands of more combinations are possible. Examples of "unnatural" amino acids include b-amino acids (3³ and b²), homo-amino acids, proline and pyruvic acid derivatives, 3-substituted alanine derivatives, glycine derivatives, ring-substituted phenylalanine and tyrosine derivatives, linear core amino acids, diamino acids, D-amino acids, and N-methyl amino acids. Unnatural or non-natural amino acids also include modified amino acids. "Modified" amino acids include amino acids (e.g., natural amino acids) that have been chemically modified to include a group, groups, or chemical moiety not naturally present in the amino acid.

In accordance with the understanding of a person skilled in the art, the peptide sequences disclosed herein are shown proceeding from left to right, with the left end of the sequence being the N-terminus of the peptide and the right end of the sequence being the C-terminus of the peptide.

Among sequences disclosed herein are sequences incorporating an "-Nhh" moiety at the carboxy terminus (C-terminus) of the sequence. An "-Nhh" moiety at the C-terminus of the sequence indicates an amino group, corresponding to the presence of an amido (-(C=0)-NH₂) group at the C-terminus.

It is further understood that the moiety at the amino terminus or carboxy terminus may be a bond, e.g., a covalent bond, particularly in situations where the amino terminus or carboxy terminus is bonded to a linker, an amide resin, or to another chemical moiety. In the case of non-proteinogenic or non-naturally occurring amino acids, unless they are referred to by their full name (e.g. sarcosine, ornithine, etc.), frequently employed three- or four-character codes are employed for residues thereof, including those abbreviations as indicated in the abbreviation list in table 1 b.

The term "L-amino acid," as used herein, refers to the "L" isomeric form of an amino acid, and conversely the term "D-amino acid" refers to the "D" isomeric form of an amino acid. The three- letter code in the form without any stereochemical specification, i.e. Ala, Arg, Asn etc., and as generally used in the present specification, shall generally comprise the D- and L- form, and mixtures thereof, unless explicitly indicated otherwise. The prefix“nor“ refers to a structural analogue which can be derived from a parent compound by the removal of one carbon atom along with the accompanying hydrogen atoms. The prefix“homo" indicates the next higher member in a homologous series. A reference to a specific isomeric form will be indicated by the capital prefix L- or D- as described above (e.g. D-Arg, L-Arg etc.). A specific reference to homo- or nor-forms will accordingly be explicitly indicated by a respective prefix (e.g. homo-Arg, h-Arg, nor-Arg, homo-Cys, h-Cys etc.). It is further a conventional manner, when using one-letter codes, to indicate the L-amino acid with a capital letter such as A, R, F, etc. and the D-amino acid with small letters such as a, r, f, and the like. Further, as used herein, nor-amino acids are being referred to with their full name, or a three-letter code as defined herein, or with the one-letter code together with“^N” or”ⁿ”, e.g. L-Nle or L^N for L-Norleucine, and D-Nle or G for D-Norleucine, as indicated to the extent used herein in the abbreviation list in table 1 b, above.

The term“halogen atom” means a fluorine, chlorine, bromine or iodine atom, particularly a fluorine, chlorine or bromine atom.

The term“Ci-C₆-alkyl” means a linear or branched, saturated, monovalent hydrocarbon group having 1 , 2, 3, 4, 5 or 6 carbon atoms, e.g. a methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl, tert- butyl, pentyl, isopentyl, 2-methylbutyl, 1-methylbutyl, 1-ethylpropyl,

1.2-dimethylpropyl, neo-pentyl, 1 ,1-dimethylpropyl, hexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1-ethylbutyl, 2-ethylbutyl, 1 ,1-dimethylbutyl, 2,2-dimethylbutyl,

3.3-dimethylbutyl, 2,3-dimethylbutyl, 1 ,2-dimethylbutyl or 1 ,3-dimethylbutyl group, or an isomer thereof. Particularly, said group has 1 , 2, 3 or 4 carbon atoms (“Ci-C₄-alkyl”), e.g. a methyl, ethyl, propyl, isopropyl, butyl, sec-butyl isobutyl, or tert- butyl group, more particularly 1 , 2 or 3 carbon atoms (“Ci-C₃-alkyl”), e.g. a methyl, ethyl, n-propyl or isopropyl group.

The term“Ci-C₃-alkoxy” means a linear or branched, saturated, monovalent group of formula (Ci-C₃-alkyl)-0-, in which the term“Ci-C₃-alkyl” is as defined supra, e.g. a methoxy, ethoxy, n-propoxy, isopropoxy group. The term“phenyl-Ci-C3-alkyl-” means a linear or branched, saturated, monovalent hydrocarbon group in which the term“Ci-C3-alkyl” is defined supra, in which one hydrogen atom is replaced by a phenyl group, and which is bonded to the rest of the molecule via the Ci-C3-alkyl portion. Said phenyl-Ci-C3-alkyl- group is, for example, benzyl, phenethyl, 1 -phenylethyl, or 3- phenylpropyl.

As used herein, the term“protecting groups” means a group attached to an atom, preferably a oxygen or nitrogen or sulfur atom in intermediates used for the preparation of compounds of the general formula (I). Such groups are introduced e.g. by chemical modification of the respective hydroxyl, amino or sulfanyl group e.g. in order to obtain chemoselectivity in a subsequent chemical reaction. Protecting groups, including methods for their introduction and removal, are well known to the person skilled in the art (see e.g. P.G.M. Wuts in Greene’s Protective Groups in Organic Synthesis, 5^th edition, Wiley 2014).

As used herein, the term“leaving group” means an atom or a group of atoms that is displaced in a chemical reaction as stable species taking with it the bonding electrons. In particular, such a leaving group is selected from the group comprising: halide, in particular fluoride, chloride, bromide or iodide, (methylsulfonyl)oxy, [(trifluoromethyl)sulfonyl]oxy, [(nonafluorobutyl)- sulfonyl]oxy, (phenylsulfonyl)oxy, [(4-methylphenyl)sulfonyl]oxy, [(4-bromophenyl)sulfonyl]oxy, [(4-nitrophenyl)sulfonyl]oxy, [(2-nitrophenyl)sulfonyl]oxy, [(4-isopropylphenyl)sulfonyl]oxy, [(2,4,6-triisopropylphenyl)sulfonyl]oxy, [(2,4,6-trimethylphenyl)sulfonyl]oxy, [(4-fe/f-butyl- phenyl)sulfonyl]oxy and [(4-methoxyphenyl)sulfonyl]oxy.

As used herein, the term“local irradiation” means the delivery of a precisely measured dose of irradiation to a defined tumor volume with as minimal damage as possible to surrounding healthy tissue (see e.g. Halperin, Edward C., Perez, Carlos A., Brady, Luther W.: Perez and Brady’s Principles and Practice of Radiation Oncology. Fifth Edition. Philadelphia: Lippincott Williams & Wilkins, a Wolters Kluwer business, 2008.)

As used herein, the term“thermal neutrons” means free neutrons with a kinetic energy of 0.025 eV, and the term“epithermal neutrons” means free neutrons with a kinetic energy of 0.025-0.4 eV (see e.g. Carron, N. J.: An Introduction to the Passage of Energetic Particles through Matter. Boca Raton: Taylor & Francis Group, LLC. 2006.)

It is possible for the compounds of general formula (I) to exist as isotopic variants. The invention therefore includes one or more isotopic variant(s) of the compounds of general formula (I), particularly compounds of general formula (I) enriched in the boron isotope ¹⁰B.

The term“Isotopic variant” of a compound or a reagent is defined as a compound exhibiting an unnatural proportion of one or more of the isotopes that constitute such a compound. The term“Isotopic variant of the compound of general formula (I)” is defined as a compound of general formula (I) exhibiting an unnatural proportion of one or more of the isotopes that constitute such a compound.

The expression“unnatural proportion” means a proportion of such isotope which is higher than its natural abundance. The natural abundances of isotopes to be applied in this context are described in“Isotopic Compositions of the Elements 1997”, Pure Appl. Chem., 70(1 ), 217-235, 1998.

Examples of such isotopes include stable and radioactive isotopes of hydrogen, boron, carbon, nitrogen, oxygen, phosphorus, sulfur, fluorine, chlorine, bromine and iodine, such as ²H (deuterium), ³H (tritium), ¹⁰B, ¹¹B, ¹¹C, ¹³C, ¹⁴C, ¹⁵N, ¹⁷0, ¹⁸0, ³²P, ³³P, ³³S, ³⁴S, ³⁵S, ³⁶S, ¹⁸F, ³⁶CI, ⁸²Br, ¹²³l, ¹²⁴l, ¹²⁵l, ¹²⁹l and ¹³¹1, respectively.

With respect to the treatment and/or prophylaxis of the disorders specified herein the isotopic variant(s) of the compounds of general formula (I) preferably contain ¹⁰B (“¹⁰B-containing compounds of general formula (I)”). The ¹⁰B boron isotope features an effective nuclear cross section of 3835(9) barn (cf. ¹H features 0.3326(7) barn, ¹¹B 0.0055(33) barn, ¹²C 0.00353(7) barn, see e.g. Sears, Valery F., Neutron News, 1992, 3, 26-37). Upon reaction with neutrons of low kinetic energy (thermal or epithermal neutrons), alpha particles (⁴He²⁺ nuclei) and lithium-7 nuclei are formed. These high linear energy transfer (LET) particles convey their lethal destructive effects only to boron-containing cells, as discussed in the background section in more detail. Since only the ¹⁰B isotope, but not the ¹¹B isotope undergoes neutron capture, ¹⁰B- enriched agents are preferred isotopic variants of the compounds of the general formula (I).

Other isotopic variants of the compounds of general formula (I) in which one or more radioactive isotopes, such as ³H or ¹⁴C, are incorporated are useful e.g. in drug and/or substrate tissue distribution studies. These isotopes are particularly preferred for the ease of their incorporation and detectability. Positron emitting isotopes such as ¹⁸F or ¹¹C may be incorporated into a compound of general formula (I). These isotopic variants of the compounds of general formula (I) are useful for in vivo imaging applications. Deuterium-containing and ¹³C-containing compounds of general formula (I) can be used in mass spectrometry analyses in the context of preclinical or clinical studies. Replacement of hydrogen by deuterium may also alter the physicochemical properties (such as for example acidity, basicity, lipophilicity and/or the metabolic profile of the molecule and may result in changes in the ratio of parent compound to metabolites or in the amounts of metabolites formed. Such changes may result in certain therapeutic advantages and hence may be preferred in some circumstances.

Isotopic variants of the compounds of general formula (I) can generally be prepared by methods known to a person skilled in the art, e.g. by employing ¹⁰B-enriched boric acid ¹⁰B(OH)3 as starting material for the preparation of carbaborane synthons used for the preparation of compounds of the general formula (I), according to the schemes and/or examples herein. ¹⁰B- enriched boric acid has become commercially available from a plethora of suppliers (e.g. Katchem spol. S r. o., Elisky Krasnohorske 123/6, 1 10 00 Josefov, Czech Republic; Boron Specialties LLC, Laboratory & Warehouse, 2301 Duss Avenue, Ste. 35, Ambridge, PA 15003 USA), in isotopic purities up to 99+%, and can be elaborated into ¹⁰B-enriched carbaborane synthons by multiple methods known to the person skilled in the art (see e.g. Yinghuai, Z., Widjaja, E., Lo Pei Sia, S., Zhan, W., enter, K., Maguire, J. A., Hosmane, N. S., Hawthorne, M.F., J. Am. Chem. Soc., 2007, 129, 6507-6512; Adams, L., Tomlinson, S., Wang, J., Hosmane, S. N., Maguire, J. A., Hosmane, N. S., Inorg. Chem. Commun., 2002, 5, 765-767.; Scholz, M., Hey-Hawkins, E., Chem. Rev., 2011 , 11 1 , 7035-7062; Grimes, Russel N.: Carboranes. Third Edition, Academic Press (Elsevier), 2016, ISBN: 9780128018941 ) Furthermore, carbaborane synthons with high isotopic enrichment of ¹⁰B up to 99+% are also commercially available from Katchem spol. s r. o., Czech Republic (http//:www.katchem.cz/en).

Deuterium can be introduced in place of hydrogen in the course of the synthesis of compounds of the general formula (I) by many methods well known to the person skilled in the art, e.g. deuterium from D₂0 can be incorporated into said compounds directly or indirectly, or by catalytic deuteration of olefinic or acetylenic bonds using deuterium gas.

The term“¹⁰B-containing compound of general formula (I)” is defined as a compound of general formula (I), in which one or more boron atom(s) in its/their natural isotopic composition is/are replaced by one or more ¹⁰B atom(s) and in which the abundance of ¹⁰B at each respective position of the compound of general formula (I) is higher than the natural abundance of ¹⁰B, which is about 20%. Particularly, in a ¹⁰B-containing compound of general formula (I), the abundance of ¹⁰B of each boron atom of the compound of general formula (I) is higher than 30%, 40%, 50%, 60%, 70% or 80%, preferably higher than 90%, 95%, 96% or 97%, even more preferably higher than 98% or 99%. It is understood that the abundance of ¹⁰B of each boron atom can be either identical with, or independent of the abundance of ¹⁰B at other boron atom(s).

In another embodiment the present invention covers a ¹⁰B-containing compound of general formula (I), in which the abundance of ¹⁰B of each boron atom of the compound of general formula (I) is higher than 90%,

In another embodiment the present invention convers a ¹⁰B-containing compound of general formula (I), in which the abundance of ¹⁰B of each boron atom of the compound of general formula (I) is higher than 98%, and isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, and mixtures of same.

In another embodiment the present invention convers a ¹⁰B-containing compound of general formula (I), in which the abundance of ¹⁰B of each boron atom of the compound of general formula (I) is higher than 99%,

Where the plural form of the word compounds, salts, polymorphs, hydrates, solvates and the like, is used herein, this is taken to mean also a single compound, salt, polymorph, isomer, hydrate, solvate or the like.

By "stable compound' or "stable structure" is meant a compound that is sufficiently robust to survive isolation to a useful degree of purity from a reaction mixture, and formulation into an efficacious therapeutic agent.

The compounds of the present invention contain centres e.g. in the peptide backbone, in the optional diaminoalkanoic acid based branching moiety DAABM, and in the saccharide based moiety Sac. The present invention covers certain isomers of the compounds disclosed and described therein.

The peptide backbone of the compounds of the present invention, such as the Example compounds, is described by the sequence

X¹ X²- L- H i s-X³- L-Arg-X⁴-X⁵- L-Lys-NH₂

The known structure-activity relationship of the structurally and functionally related peptide a-MSH (Sahm et al., Peptides 1994, 15, 1297-1302; Sugg et al., Biopolymers 1986, 25, 2029- 2042) indicates that certain amino acids within said sequence, namely X¹, X², X³, X⁴ and X⁵ can be present as the natural, proteinogenic L-enantiomer, its D-enantiomer, or mixtures thereof; some of them, such as X¹, X⁵ and in particular X² can even represent different (but still structurally related) amino acids, none of said modifications substantially influencing the binding behaviour towards human melanocortin 1 receptors. Other amino acids in this sequence, most notably L-His and L-Arg, need to be present as the naturally occurring, proteinogenic L-form to maintain high affinity of the resulting peptide towards human melanocortin 1 receptors. Further, L-Lys is modified through conjugation to saccharide functionalised carbaborane moieties as described and defined herein, and it can have a side chain of different length e.g. such as in L- ornithine or in (2S)-2,3-diaminopropionic acid.

Hence, within the coverage of the present invention, X¹ represents an amino acid selected from L-norleucine, D-norleucine, norleucine as isomeric mixture, L-methionine, D-methionine, and methionine as isomeric mixture, X² represents an amino acid selected from L-alanine, D-alanine, alanine as isomeric mixture, L-glutamic acid, D-glutamic acid, glutamic acid as isomeric mixture, L-aspartic acid, D-aspartic acid, aspartic acid as isomeric mixture, L-serine, D-serine, and serine as isomeric mixture, L-His represents L-histidine, X³ represents an amino acid selected from D- phenylalanine, L-phenylalanine, and phenylalanine as isomeric mixture, L-Arg represents L- arginine, X⁴ represents an amino acid selected from L-tryptophan, D-tryptophan, and tryptophan as isomeric mixture and X⁵ represents an amino acid selected from glycine, L-alanine, D-alanine, and alanine as isomeric mixture. In another embodiment of the present invention, X¹ represents an amino acid selected from L- norleucine and L-methionine, X² represents an amino acid selected from L-alanine, L-glutamic acid and L-aspartic acid, L-His represents L-histidine, X³ represents an amino acid selected from D-phenylalanine, L-phenylalanine, and phenylalanine as isomeric mixture, L-Arg represents L- arginine, X⁴ represents an amino acid selected from L-tryptophan, D-tryptophan, and tryptophan as isomeric mixture and X⁵ represents an amino acid selected from glycine, L-alanine, D-alanine, and alanine as isomeric mixture.

In another embodiment of the present invention, X¹ represents L-norleucine, X² represents L- aspartic acid, L-His represents L-histidine, X³ represents D-phenylalanine, L-Arg represents L- arginine, X⁴ represents L-tryptophan, and X⁵ represents glycine.

In another embodiment of the present invention, X¹ represents an amino acid selected from L- norleucine, D-norleucine, norleucine as isomeric mixture, L-methionine, D-methionine, and methionine as isomeric mixture, X² represents L-aspartic acid, L-His represents L-histidine, X³ represents D-phenylalanine, L-Arg represents L-arginine, X⁴ represents L-tryptophan, and X⁵ represents glycine.

In another embodiment of the present invention, X¹ represents L-norleucine, X² represents an amino acid selected from L-alanine, D-alanine, alanine as isomeric mixture, L-glutamic acid, D- glutamic acid, glutamic acid as isomeric mixture, L-aspartic acid, D-aspartic acid, aspartic acid as isomeric mixture, L-serine, D-serine, and serine as isomeric mixture, L-His represents L- histidine, X³ represents D-phenylalanine, L-Arg represents L-arginine, X⁴ represents L- tryptophan, and X⁵ represents glycine.

In another embodiment of the present invention, X¹ represents L-norleucine, X² represents L- aspartic acid, L-His represents L-histidine, X³ represents an amino acid selected from D- phenylalanine, L-phenylalanine, and phenylalanine as isomeric mixture, L-Arg represents L- arginine, X⁴ represents L-tryptophan, and X⁵ represents glycine.

In another embodiment of the present invention, X¹ represents L-norleucine, X² represents L- aspartic acid, L-His represents L-histidine, X³ represents D-phenylalanine, L-Arg represents L- arginine, X⁴ represents an amino acid selected from L-tryptophan, D-tryptophan, and tryptophan as isomeric mixture, and X⁵ represents glycine.

In another embodiment of the present invention, X¹ represents L-norleucine, X² represents L- aspartic acid, L-His represents L-histidine, X³ represents D-phenylalanine, L-Arg represents L- arginine, X⁴ represents L-tryptophan, and X⁵ represents represents an amino acid selected from glycine, L-alanine, D-alanine, and alanine as isomeric mixture. The compounds of the invention may contain one or more diaminoalkanoic acid based branching moieties of the structure

DAABM

in which q is as defined for the compounds of the general formula (I), said diaminoalkanoic acid based branching moieties being herein also referred to as DAABM. Particularly, said DAABM is derived from 2,3-diaminopropionic acid (Dap). Said DAABM allow for the attachment of two or more (if more than one DAABM is attached) carbaborane synthons to the e-amino group of the side chain of the C-terminal L-lysine. Said diaminoalkanoic acids, such as 2,3-diaminopropionic acid, featuring one stereogenic centre, can be present as (2S)-enantiomer, as (2R)-enantiomer, and mixtures thereof. The present invention covers all stereoisomeric forms of the compounds of general formula (I) resulting from the presence of (2S)-diaminoalkanoic acid (also referred to herein as (2S)-DAABM), (2R)-diaminoalkanoic acid (also referred to herein as (2R)-DAABM), and stereoisomeric mixtures thereof, particularly of (2S)-2,3-diaminopropionic acid (also referred to herein as (2S)-Dap), (2R)-2,3-diaminopropionic acid, and mixtures thereof, as branching moieties as described supra.

The compounds of the present invention feature a saccharide based unit Sac, which represents, as defined for the compounds of general formula (I), a group selected from

Scheme 1a: Sac groups as defined for the compounds of general formula (I)

The monosaccharides from which said saccharide based units Sac are derived are known to undergo isomerisation reactions referred to as mutarotation in the literature (see e.g. Pazourek, J. Sep. Sci. 2010, 33, 974-981 ), inter alia in aqueous solution, as shown for D-monosaccarides below in Scheme 1 b, in which (Sac-I) represents the a-D-pyranose form, (Sac-ll) represents the open-chain D-aldose form, (Sac-Ill) represents the b-D-pyranose form, (Sac-IV) represents the b-D-furanose form, and (Sac-V) represents the a-D-furanose form. The reader is referred to the fact that the Sac units shown in Scheme 1a, above, reflect both the a- and b-pyranose forms, corresponding e.g. to (Sac-I) and (Sac-Ill), already.

(Sac-V)

Scheme 1b: Mutarotation reactions of Sac units derived from D-monosaccharides

Likewise, this is shown for L-monosaccharides in Scheme 1c, in which (Sac-VI) represents the a-L-pyranose form, (Sac-VII) represents the open-chain L-aldose form, (Sac-VIII) represents the b-L-pyranose form, (Sac-IX) represents the b-L-furanose form, and (Sac-X) represents the a-L- furanose form.

(Sac-X)

Scheme 1c: Mutarotation reactions of Sac units derived from L-monosaccharides

Specifically for 6-deoxy-D-galactose, from which Examples 1 - 3 are derived, this is shown below in Scheme 1 d, in which (Sac-XI) represents a Sac unit derived from 6-deoxy-oD- galactopyranose, (Sac-XII) represents the corresponding open-chain D-aldose form, (Sac-XIII) represents a Sac unit derived from 6-deoxy-3-D-galactopyranose, (Sac-XIV) represents a Sac unit derived from 6-deoxy-3-D-galactofuranose, and (Sac-XV) represents a Sac unit derived from 6-deoxy-oD-galactofuranose.

(Sac-XV)

Scheme 1d: Mutarotation reactions of Sac units derived from 6-deoxy-D-galactose

The isomeric forms of Sac units resulting from abovementioned mutarotation reactions, as illustrated in Schemes 1 a, 1 b, 1 c, and, as a specific example, for 6-deoxy-D-galactose in Scheme 1 d, are included within the scope of the present invention, and are collectively being referred to herein as“isomers resulting from mutarotation reactions” herein. Hence, the present invention covers compounds of formula (I), and isomers resulting from mutarotation reactions thereof, in which the Sac units as defined for the compounds of formula (I) may exist in a single isomeric form, or as a mixture of a- and b-pyranose forms, or as a mixture of two or more isomeric forms as shown in Schemes 1 b, 1c, or 1 d, as the case may be. Further, by virtue of the symmetry properties of the carbaborane core, its positions 1 and 7 in 9- monosubstituted carbaborane intermediates are not topologically identical, i.e. not interchangable by rotation as shown in the Scheme 1 e below.

Scheme 1e: Topological features of carbaborane core positions 1 and 7

Therefore, regioisomeric mixtures may result when substituents, such as those derived from the monosaccharide intermediates disclosed herein (e.g. Intermediate 7 in the Experimental Section; see also formula (XV) in Scheme 7a), are attached to said position 1 or 7, as the case may be. Hence, the display of a carbaborane moiety Cb substituted at one of said positions 1 and 7, as exemplarily shown in Scheme 1f, below, and also in the claims and the specification herein refers to a respective compound featuring said substitution at position 1 (but not at position 7), or a respective compound featuring said substitution at position 7 (but not at position 1 ), or a regioisomeric mixture thereof. This also applies to instances where reference is made to such substitution at a position corresponding to position 1 , such as in the Experimental section for Intermediates 8 to 10. Accordingly, and as far as compounds with one monosaccharide based substituent attached to position 1 or 7 are concerned, the present invention covers compounds of formula (I) featuring said monosubstitution at position 1 , compounds featuring said monosubstitution at position 7, and regioisomeric mixtures thereof

Sac

Scheme 1f: Carbaborane moiety Cb encoding for substitution at position 1 , position 7, or a regioisomeric mixture reflecting both monosubstitutions. The purification of the compounds of the present invention can be accomplished by standard separation and purification techniques known in the art, in particular by the use of reversed- phase-HPLC, e.g., as described herein, using columns such as a Phenomenex Biphenyl (5 pm, 100 A, Biphenyl, 250 x 21.2 mm, Phenomenex Jupiter 5 pm 300 A, C18, 250 x 21.2 mm, Phenomenex Proteo 10 pm 90 A, C12, 250 x 21.2 mm, Phenomenex Kinetex 5 pm 100 A, C18, 250 x 10 mm, or, preferably, Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm. This may, besides chemical purification, also result in separation of isomers amenable to separation on non-chiral phase, such as diastereomers. Separation of stereoisomers can be further addressed by chiral chromatography (/^'.e., HPLC columns using a chiral phase), with or without conventional derivatisation, optimally chosen to maximise the separation of the stereoisomers. Suitable HPLC columns using a chiral phase are commercially available, such as those manufactured by Daicel, e.g., Chiracel OD and Chiracel OJ, for example, among many others, which are all routinely selectable.

In order to distinguish different types of isomers from each other reference is made to IUPAC Rules Section E (Pure Appl. Chem. 1976, 45, 11-30).

Further, it is possible for the compounds of the present invention to exist as tautomers. For example, any compound of the present invention which contains a histidine as an amino acid for example can exist as as tautomers with regard to the imidazole ring therein, or even a mixture in any amount of the two tautomers, namely:

The present invention includes all possible tautomers of the compounds of the present invention as single tautomers, or as any mixture of said tautomers, in any ratio.

Further, the compounds of the present invention can exist as N-oxides, which are defined in that at least one nitrogen of the compounds of the present invention is oxidised. The present invention includes all such possible N-oxides.

The present invention also covers useful forms of the compounds of the present invention, such as metabolites, hydrates, solvates, salts, in particular pharmaceutically acceptable salts, and/or co-precipitates.

The compounds of the present invention can exist as a hydrate, or as a solvate, wherein the compounds of the present invention contain polar solvents, in particular water, methanol or ethanol for example, as structural element of the crystal lattice of the compounds. It is possible for the amount of polar solvents, in particular water, to exist in a stoichiometric or non- stoichiometric ratio. In the case of stoichiometric solvates, e.g. a hydrate, hemi-, (semi-), mono- , sesqui-, di-, tri-, tetra-, penta- etc. solvates or hydrates, respectively, are possible. The present invention includes all such hydrates or solvates.

Further, it is possible for the compounds of the present invention to exist in free form, e.g. as a free base, or as a free acid, or as a zwitterion, or to exist in the form of a salt. Said salt may be any salt, either an organic or inorganic addition salt, particularly any pharmaceutically acceptable organic or inorganic addition salt, which is customarily used in pharmacy, or which is used, for example, for isolating or purifying the compounds of the present invention.

The term“pharmaceutically acceptable salt" refers to an inorganic or organic acid addition salt of a compound of the present invention. For example, see Berge, et al.“Pharmaceutical Salts,” J. Pharm. Sci. 1977, 66, 1 -19.

A suitable pharmaceutically acceptable salt of the compounds of the present invention may be, for example, an acid-addition salt of a compound of the present invention bearing a nitrogen atom, in a chain or in a ring, for example, which is sufficiently basic, such as an acid-addition salt with an inorganic acid, or“mineral acid”, such as hydrochloric, hydrobromic, hydroiodic, sulfuric, sulfamic, bisulfuric, phosphoric, or nitric acid, for example, or with an organic acid, such as formic, acetic, acetoacetic, pyruvic, trifluoroacetic, propionic, butyric, hexanoic, heptanoic, undecanoic, lauric, benzoic, salicylic, 2-(4-hydroxybenzoyl)-benzoic, camphoric, cinnamic, cyclopentanepropionic, digluconic, 3-hydroxy-2-naphthoic, nicotinic, pamoic, pectinic, 3- phenylpropionic, pivalic, 2-hydroxyethanesulfonic, itaconic, trifluoromethanesulfonic, dodecylsulfuric, ethanesulfonic, benzenesulfonic, para-toluenesulfonic, methanesulfonic, 2-naphthalenesulfonic, naphthalinedisulfonic, camphorsulfonic acid, citric, tartaric, stearic, lactic, oxalic, malonic, succinic, malic, adipic, alginic, maleic, fumaric, D-gluconic, mandelic, ascorbic, glucoheptanoic, glycerophosphoric, aspartic, sulfosalicylic, or thiocyanic acid, for example.

Further, another suitably pharmaceutically acceptable salt of a compound of the present invention which is sufficiently acidic, is an alkali metal salt, for example a sodium or potassium salt, an alkaline earth metal salt, for example a calcium, magnesium or strontium salt, or an aluminium or a zinc salt, or an ammonium salt derived from ammonia or from an organic primary, secondary or tertiary amine having 1 to 20 carbon atoms, such as ethylamine, diethylamine, triethylamine, ethyldiisopropylamine, monoethanolamine, diethanolamine, triethanolamine, dicyclohexylamine, dimethylaminoethanol, diethylaminoethanol, tris(hydroxymethyl)aminomethane, procaine, dibenzylamine, /V-methylmorpholine, arginine, lysine, 1 ,2-ethylenediamine, /V-methylpiperidine, /V-methyl-glucamine, /V,/V-dimethyl-glucamine, /V-ethyl-glucamine, 1 ,6-hexanediamine, glucosamine, sarcosine, serinol, 2-amino-1 ,3- propanediol, 3-amino-1 ,2-propanediol, 4-amino-1 ,2,3-butanetriol, or a salt with a quarternary ammonium ion having 1 to 20 carbon atoms, such as tetramethylammonium, tetraethylammonium, tetra(n-propyl)ammonium, tetra(n-butyl)ammonium, /V-benzyl-/V,/V,/V- trimethylammonium, choline or benzalkonium.

Those skilled in the art will further recognise that it is possible for acid addition salts of the claimed compounds to be prepared by reaction of the compounds with the appropriate inorganic or organic acid via any of a number of known methods. Alternatively, alkali and alkaline earth metal salts of acidic compounds of the present invention are prepared by reacting the compounds of the present invention with the appropriate base via a variety of known methods.

The present invention includes all possible salts of the compounds of the present invention as single salts, or as any mixture of said salts, in any ratio.

In the present text, in particular in the Experimental Section, for the synthesis of intermediates and of examples of the present invention, when a compound is mentioned as a salt form with the corresponding base or acid, the exact stoichiometric composition of said salt form, as obtained by the respective preparation and/or purification process, is, in most cases, unknown.

Unless specified otherwise, suffixes to chemical names or structural formulae relating to salts, such as "hydrochloride", "trifluoroacetate", "sodium salt", or "x HCI", "x CF3COOH", "x Na⁺", for example, mean a salt form, the stoichiometry of which salt form not being specified.

This applies analogously to cases in which synthesis intermediates or example compounds or salts thereof have been obtained, by the preparation and/or purification processes described, as solvates, such as hydrates, with (if defined) unknown stoichiometric composition.

Furthermore, the present invention includes all possible crystalline forms, or polymorphs, of the compounds of the present invention, either as single polymorph, or as a mixture of more than one polymorph, in any ratio.

In accordance with a second embodiment of the first aspect, the present invention covers compounds of general formula (I), supra, in which:

R¹ represents a group R²-C(=0)-, in which R² represents a group selected from Ci-C₃-alkyl and phenyl, in which the phenyl group is optionally substituted, one, two or three times, identically or differently, with a group selected from a fluorine atom, a chlorine atom, methyl and methoxy,

X¹ represents an amino acid selected from L-norleucine and L-methionine,

X² represents an amino acid selected from L-alanine, L-glutamic acid and L-aspartic acid,

L-His represents L-histidine,

L-Arg represents L-arginine,

r represents an integer selected from 1 , 2 and 3,

CbD represents a group selected from

Cb-$,

which q represents an integer 1 ,

$ represents the point of attachment to the rest of the molecule, Cb represents a group

Sac represents a group selected from

and

represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group Cb,

and isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, and mixtures of same. In accordance with a third embodiment of the first aspect, the present invention covers compounds of general formula (I), supra, in which:

R¹ represents a group R²-C(=0)-, in which R² represents a group selected from Ci-C3-alkyl and phenyl,

X¹ represents an amino acid selected from L-norleucine and L-methionine,

L-His represents L-histidine,

L-Arg represents L-arginine,

r represents an integer selected from 2 and 3,

CbD represents a group selected from

Cb-$,

which q represents an integer 1 ,

$ represents the point of attachment to the rest of the molecule,

Cb represents a group

Sac represents a group selected from

boron atom which is bonded to a hydrogen atom in addition to the bonds shown within the group Cb, and

represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group Cb,

In accordance with a fourth embodiment of the first aspect, the present invention covers compounds of general formula (I), supra, in which:

X¹ represents L-norleucine,

X² represents L-aspartic acid,

L-His represents L-histidine,

X³ represents D-phenylalanine,

L-Arg represents L-arginine,

X⁴ represents L-tryptophan,

X⁵ represents glycine,

r represents an integer selected from 2 and 3,

CbD represents a group selected from Cb-$,

which

q represents an integer 1 ,

$ represents the point of attachment to the rest of the molecule,

Cb represents a group

Sac represents a group selected from

represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group Cb,

In accordance with a fifth embodiment of the first aspect, the present invention covers compounds of general formula (I), supra, in which:

R¹ represents a group CH₃-C(=0)-,

X¹ represents L-norleucine,

X² represents L-aspartic acid,

L-His represents L-histidine,

X³ represents D-phenylalanine,

L-Arg represents L-arginine, X⁴ represents L-tryptophan,

X⁵ represents glycine,

r represents an integer 3,

CbD represents a group selected from

Cb-$,

which q represents an integer 1 ,

$ represents the point of attachment to the rest of the molecule,

Cb represents a group

Sac

Sac represents a group

oron atom which is bonded to a hydrogen atom in addition to the bonds shown within the group Cb, and

“o” represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group

Cb,

and isomers resulting from mutarotation reactions, tautomers, hydrates, solvates, and salts thereof, and mixtures of same. Further embodiments of the first aspect of the present invention:

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which R¹ represents a group R²-C(=0)-, in which R² represents a group selected from Ci-C₃-alkyl, benzyl and phenyl, in which the phenyl group, and the phenyl present in the benzyl group, are optionally substituted, one, two or three times, identically or differently, with a group selected from a fluorine atom, a chlorine atom, methyl and methoxy,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which R¹ represents a group R²-C(=0)-, in which R² represents a group selected from Ci-C₃-alkyl and phenyl, in which the phenyl group is optionally substituted, one, two or three times, identically or differently, with a group selected from a fluorine atom, a chlorine atom, methyl and methoxy,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which R¹ represents a group R²-C(=0)-, in which R² represents a group selected from Ci-C₃-alkyl and phenyl,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which R¹ represents a group R²-C(=0)-, in which R² represents a Ci-C₃-alkyl group, and isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, and mixtures of same.

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which R¹ represents a group R²-C(=0)-, in which R² represents a phenyl group, and isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, and mixtures of same. In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which R¹ represents a group R²-C(=0)-, in which R² represents a Ci-C₂-alkyl group, and isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, and mixtures of same.

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which R¹ represents a group C₂H₅-C(=0)-,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which R¹ represents a group CH₃-C(=0)-,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which R¹ represents a group R²-C(=0)-, in which R² represents a Ci-C₂-alkyl group, and isomers resulting from mutarotation reactions, tautomers, hydrates, solvates, and salts thereof, and mixtures of same.

and isomers resulting from mutarotation reactions, tautomers, hydrates, solvates, and salts thereof, and mixtures of same.

and isomers resulting from mutarotation reactions, tautomers, N-oxides, solvates, and salts thereof, and mixtures of same.

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which X¹ represents an amino acid selected from L-norleucine and L-methionine, X² represents an amino acid selected from L-alanine, L-glutamic acid and L-aspartic acid, L-His represents L-histidine, X³ represents an amino acid selected from D-phenylalanine, L- phenylalanine, and phenylalanine as isomeric mixture, L-Arg represents L-arginine, X⁴ represents an amino acid selected from L-tryptophan, D-tryptophan, and tryptophan as isomeric mixture and X⁵ represents an amino acid selected from glycine, L-alanine, D-alanine, and alanine as isomeric mixture,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which X¹ represents L-norleucine, X² represents L-aspartic acid, L-His represents L-histidine, X³ represents D-phenylalanine, L-Arg represents L-arginine, X⁴ represents L- tryptophan, and X⁵ represents glycine,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which X¹ represents an amino acid selected from L-norleucine, D-norleucine, norleucine as isomeric mixture, L-methionine, D-methionine, and methionine as isomeric mixture, X² represents L-aspartic acid, L-His represents L-histidine, X³ represents D- phenylalanine, L-Arg represents L-arginine, X⁴ represents L-tryptophan, and X⁵ represents glycine,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which X¹ represents L-norleucine, X² represents an amino acid selected from L- alanine, D-alanine, alanine as isomeric mixture, L-glutamic acid, D-glutamic acid, glutamic acid as isomeric mixture, L-aspartic acid, D-aspartic acid, aspartic acid as isomeric mixture, L-serine, D-serine, and serine as isomeric mixture, L-His represents L-histidine, X³ represents D- phenylalanine, L-Arg represents L-arginine, X⁴ represents L-tryptophan, and X⁵ represents glycine,

and isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, and mixtures of same. In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which X¹ represents L-norleucine, X² represents L-aspartic acid, L-His represents L-histidine, X³ represents an amino acid selected from D-phenylalanine, L-phenylalanine, and phenylalanine as isomeric mixture, L-Arg represents L-arginine, X⁴ represents L-tryptophan, and X⁵ represents glycine,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which X¹ represents L-norleucine, X² represents L-aspartic acid, L-His represents L-histidine, X³ represents D-phenylalanine, L-Arg represents L-arginine, X⁴ represents an amino acid selected from L-tryptophan, D-tryptophan, and tryptophan as isomeric mixture, and X⁵ represents glycine,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which X¹ represents L-norleucine, X² represents L-aspartic acid, L-His represents L-histidine, X³ represents D-phenylalanine, L-Arg represents L-arginine, X⁴ represents L- tryptophan, and X⁵ represents represents an amino acid selected from glycine, L-alanine, D- alanine, and alanine as isomeric mixture,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which CbD represents a group selected from: Cb-$,

which q represents an integer 1 ,

$ represents the point of attachment to the rest of the molecule,

Cb represents a group

Sac represents a group

“o” represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group

Cb,

and isomers resulting from mutarotation reactions, tautomers, hydrates, solvates, and salts thereof, and mixtures of same. In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which CbD represents a group selected from:

Cb-$, in which

$ represents the point of attachment to the rest of the molecule,

Cb represents a group

Sac represents a group

represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group Cb,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which CbD represents a group selected from:

Cb

^HINcH_2)q

, in which

q represents an integer 1 ,

$ represents the point of attachment to the rest of the molecule,

Cb represents a group Sac

Sac represents a group

“o” represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group

Cb,

. . .

, in which q represents an integer 1 ,

$ represents the point of attachment to the rest of the molecule,

Cb represents a group Sac

Sac represents a group

“o” represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group

Cb,

Cb-$,

which q represents an integer 1 ,

$ represents the point of attachment to the rest of the molecule,

Cb represents a group

Sac represents a group

represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group Cb,

, in which q represents an integer 1 ,

$ represents the point of attachment to the rest of the molecule,

Cb represents a group

Sac represents a group

“o” represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group

Cb,

, in which

q represents an integer 1 ,

$ represents the point of attachment to the rest of the molecule,

Cb represents a group

Sac

Sac represents a group

“·” represents a boron atom which is bonded to a hydrogen atom in addition to the bonds shown within the group Cb, and

“o” represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group

Cb,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which Sac represents a group selected from:

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which Sac represents a group:

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which q represents an integer selected from 1 , 2 and 3,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which q represents an integer selected from 1 and 2,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which q represents an integer 1 , and isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, and mixtures of same.

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which q represents an integer 2,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which q represents an integer 1 ,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which r represents an integer selected from 0, 1 , 2 and 3,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which r represents an integer selected from 1 , 2, 3 and 4,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which r represents an integer selected from 2, 3 and 4,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which r represents an integer selected from 1 , 2 and 3,

and isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, and mixtures of same. In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which r represents an integer selected from 2 and 3,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which r represents an integer 2,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which r represents an integer 3,

In a further embodiment of the first aspect, the present invention covers compounds of formula (I), supra, in which r represents an integer selected from 2 and 3,

and isomers resulting from mutarotation reactions, tautomers, hydrates, solvates, and salts thereof, and mixtures of same. In a further embodiment of the first aspect, the present invention covers compounds of formula

(I), supra, in which the number of carbaborane moieties per molecule of formula (I) is selected from 1 , 2 and 4,

In a further embodiment of the first aspect, the present invention covers compounds of formula

(I), supra, in which the number of carbaborane moieties per molecule of formula (I) is selected from 2 and 4,

(I), supra, in which the number of carbaborane moieties per molecule of formula (I) is 4,

and isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, and mixtures of same. In a further embodiment of the first aspect, the present invention covers compounds of formula

Sac

In a particular further embodiment of the first aspect, the present invention covers combinations of two or more of the above mentioned embodiments under the heading“further embodiments of the first aspect of the present invention”.

The present invention covers any sub-combination within any embodiment or aspect of the present invention of compounds of general formula (I), supra.

The present invention covers any sub-combination within any embodiment or aspect of the present invention of intermediate compounds of general formula (XIX).

The present invention covers the compounds of general formula (I) which are disclosed in the Example Section of this text, infra.

General synthesis of the compounds of the present invention

The following paragraph describes the synthesis of the compounds of the present invention in general terms. For abbreviations used, the reader is referred to table 3, which immediately precedes the Experimental Section. Protecting groups, as referred to herein, including methods for their introduction and removal, are well known to the person skilled in the art (see e.g. P.G.M. Wuts in Greene’s Protective Groups in Organic Synthesis, 2014, 5^th edition, Wiley).

The schemes and procedures described below illustrate synthetic routes to the compounds of general formula (I) of the invention and are not intended to be limiting. It is clear to the person skilled in the art that the order of transformations as exemplified in schemes 3, 4, 6a, 6b and 7a can be modified in various ways. The usage of protecting groups, reagents, and the order the transformations exemplified is therefore not intended to be limiting.

The compounds according to the invention of general formula (I) can be prepared by Fmoc- based solid phase peptide synthesis using an automated peptide synthesizer such as a SYRO I, by MultiSynTech at a temperature ranging from 0°C to 50 °C, preferably at room temperature. As solid phase, an amide resin can be used, such as a NovaSyn® TGR R resin (commercially available e.g. from Novabiochem, Darmstadt, Germany) or, preferably, a Rink amide resin (commercially available e.g. from Iris Biotech). The solid phase peptide synthesis reaction can be performed on a 2 - 100 pmol scale, preferably on a 2 - 30 pmol scale, more preferably on a 5 - 15 pmol scale. To accomplish the reaction, the respective amino acid and the reagents Oxyma and DIC can be added in 5-10-fold, preferably 8-fold molar excess, using DMF as solvent. The used amino acids are /V-protected, preferably /V-oFmoc-protected. Additional protecting groups for blocking of side chain functionalities can be advantageously used. Such /V-protected amino acids, with and without protecting groups for side chain functional groups, are well known to the person skilled in the art, and are widely commercialy available. Likewise, protecting groups for the /V-terminal groups and for side chain functional groups are known to the person skilled in the art, and are herein e.g. selected from Fmoc, tBu, Mpe, 2-Ph'Pr, TEGBn, Trt, Mmt, Mtt, Tos, Boc, Doc, Bom, Bum, Dde, TBDMS, Pbf, Pmc, Mtr, MIS, Hoc, and Mts, see table 3 for full names, and table 1c for structural formulae). Each coupling step can be performed one or more times to effect advantageous turnover, preferably two times, for a time between 30 and 60 minutes, preferably for 40 minutes. Cleavage of the /V-terminal Fmoc protecting group can be accomplished by methods known to the person skilled in the art, preferably using 40 % piperidine in DMF for 3 min and afterwards 20 % piperidine in DMF for 10 min. This cycle of coupling and Fmoc cleavage reactions can be repeated until the desired peptide length was achieved, to give resin-bonded intermediates of formula (II) shown below in Scheme 2, in which

X¹, X³, X⁵, and r are as defined for the general formula (I)

X^2P represents L-alanine, D-alanine or alanine as isomeric mixture, or a side chain protected amino acid selected from L-Asp(PG⁴), D-Asp(PG⁴), Asp(PG⁴) as isomeric mixture, L-Glu(PG⁴), D-Glu(PG⁴), Glu(PG⁴) as isomeric mixture, L-Ser(PG⁵), D-Ser(PG⁵), and Ser(PG⁵) as isomeric mixture, preferably L-Asp(tBu) and L-Glu(tBu),

X^4P represents a side chain protected amino acid selected from L-Trp(PG⁵), D- Trp(PG⁶), and Trp(PG⁶) as isomeric mixture,

PG¹ represents a protecting group selected from Trt, Mtt, Mmt, Tos, Boc, Doc, Bom, and Bum, preferably Trt,

PG² represents a protecting group selected from Pbf, Pmc, Mtr, and MIS, preferably Pbf,

PG³ represents a protecting group selected from Boc, Dde, and Mtt, preferably Boc,

PG⁴ represents a protecting group selected from tBu, Mpe, 2-Ph'Pr, and TGEBn, preferably tBu,

PG⁵ represents a protecting group selected from tBu, Trt, and TBDMS, preferably tBu, PG⁶ represents a protecting group selected from Boc, Hoc, and Mts, preferably Boc, and in which

represents the amide resin to which the remaining portion of formula (II) is bonded, preferably a Rink amide resin.

In between the reaction steps, the resins can be advantageously washed with solvents to remove excess of reagents.

Scheme 2: Resin-bonded intermediates of formula (II).

Subsequently, said resin-bonded peptides of formula (II) can be prepared for further elaboration of the side chain of the C-terminal L-amino acid, e.g. L-lysine, by reaction of the N-terminal amino group (located at X^1P) with an acylation agent, such as acetic acid anhydride, in the presence of an organic base, such as DIPEA, in a solvent such as a halogenated aliphatic hydrocarbon, e.g. dichloromethane, to give an acylated resin-bonded-peptide of formula (III), in which R¹ represents a group R²-C(=0)-, as defined for the compounds of the gerneal formula (I), followed by selective cleavage of the protecting group PG³ attached to the amino group of the side chain of the C-terminal L-amino acid, such as the e-amino group of the side chain of a C-terminal L- lysine, to give a resin-bonded peptide of formula (IV). Said cleavage can, dependent on the protecting group PG³, be accomplished by methods well known to the person skilled in the art, such as the use of a solution of hydrazine in DMF, e.g. 3 % of hydrazine in DMF, if PG³ represents Dde, or the use of a solution of 1 % TFA and 5 % TIS in dichloromethane, if PG³ represents Mtt.

Scheme 3: Conversion of intermediates of formula (II) into resin-bonded peptides of formula (IV).

Optionally, one or more diaminoalkanoic acid based branching moieties DAABM as defined supra, particularly Dap (representing 2,3-diaminopropionic acid), can be introduced by coupling a bis-/V-protected DAABM building block, preferably Fmoc-(2S)-Dap(Fmoc)-OH (V), to the the amino group of the C-terminal L-amino acid, such as the e-amino group of the side chain of a C- terminal L-lysine, in a resin-bonded intermediate of formula (IV).

Up to three of said DAABM branching moieties constitute an optional feature of the group CbD, as defined for the compound of the general formula (I), and form said CbD group together with a carbaborane moiety Cb as defined for the compounds of the general formula (I).

Within the scope of the present invention, diaminoalkanoic acid based branching moieties, featuring one stereogenic centre, can be present as (2S)-enantiomer, as (2R)-enantiomer, and mixtures thereof, which are collectively referred to herein as DAABM. Accordingly, 2,3- diaminopropionic acid can be present as (2S)-enantiomer, as (2F?)-enantiomer, and mixtures thereof, which are collectively referred to herein as Dap. In the synthesis of those example compounds featuring a 2,3-diaminopropionic acid branching moiety, the (2S)-enantiomer ((2 S)- 2,3-diaminopropionic acid, referred to herein (2S)-Dap) has been used.

This approach is visualised below in Scheme 4. Coupling of the resin-bound intermediates of formula (IV) with the branching moiety can be accomplished by reacting the amino group of the C-terminal L-amino acid, such as the e-amino group of the side chain of a C-terminal L-lysine, in formula (IV) with bis-/V-protected DAABM building blocks, particularly Dap building blocks, preferably Fmoc-(2S)-Dap(Fmoc)-OH (V), in 2- to 5-fold molar excess, in the presence of HOBt and DIC in 3- to 5-fold molar excess, in DMF as a solvent, to give the intermediate coupling product as indicated in formula (VI), followed by deprotection of the protecting groups attached to the DAABM amino groups, e.g. by Fmoc cleavage with piperidine in DMF, particularly 30 % piperidine in DMF, to give the DAABM branched resin-bonded peptides as indicated in formula (VII). Said branching cycle can be performed once or repeated according to the desired carbaborane loading of the peptide, using up to 10-fold molar excesses each of the respective with bis-/V-protected DAABM building block, preferably Fmoc-(2S)-Dap(Fmoc)-OH, HOBt, and DIC, respectively. Specific examples are described in the Experimental Section.

Fmoc

Scheme 4: Optional introduction of a (2S)-Dap branching group to the the amino group of the C- terminal L-amino acid, such as the e-amino group of the side chain of a C-terminal L-lysine, of a resin-bonded intermediate of formula (IV).

The reader is referred to the fact that selective deprotection is possible if the two amino groups present in said diaminoalkanoic acid, e.g. in 2,3-diaminopropionic acid, are protected by different protecting groups allowing for selective cleavage, as present in Fmoc-Dap(Mtt)-OH, for example, allowing for the selective removal of the Fmoc group, e.g. using 20 % piperidine in DMF, without affecting the Mtt group. This approach has been used e.g. for the introduction of Tam fluorescence labels in some reference example compounds disclosed herein, which are however not within the scope of the present invention. Specific examples are described in the Experimental Section. The respective carbaborane synthons of formula (VIII), which in turn are selected from the formulae (Vlll-a), (Vlll-b), (Vlll-c), (Vlll-d), (Vlll-e), (Vlll-f), (Vlll-g), (Vlll-h), (Vlll-i), (Vlll-j), (VIII- k), (Vlll-m), (Vlll-n), (Vlll-o), (Vlll-p), and (Vlll-q) shown in Scheme 5, in which PG⁷, PG⁸, PG⁹, PG¹⁰ represent protecting groups suitable for the protection of hydroxy groups on saccharides, such as benzyl or acetyl or in which, preferably, two groups selected from PG⁷, PG⁸, PG⁹, PG¹⁰ attached to hydroxy groups on adjacent carbon atoms together form a group -C(CH3)2-, can be subsequently attached to the amino group of the C-terminal L-amino acid, such as the e-amino group of the side chain of a C-terminal L-lysine, in resin-bonded intermediates of formula (IV), or amino groups of one or more DAABM, particularly branching moieties Dap (see formula (VII)), by coupling in 1- to 4-fold, preferably 1- to 2-fold excess per free amino group, in the presence of HOBt and DIC in 2- to 8-fold, preferably 2- to 4-fold excess per free amino group, as illustrated in Schemes 6a and 6b, below, to give conjugates as illustrated in formulae (IX) and (XI). Carbaborane synthons of formula (Vlll-n), being derived from 6-deoxy-D-galactose, are preferred, of which the carbaborane ml J9b synthon of formula (Vlll-n-a) is particularly preferred. Specific examples are described in the Experimental Section.

Table 2, below, shows the correlation of the carbaborane synthons of formulae (Vlll-a), (Vlll-b), (Vlll-c), (Vlll-d), (Vlll-e), (Vlll-f), (Vlll-g), (Vlll-h), (Vlll-i), (Vlll-j), (Vlll-k), (Vlll-m), (Vlll-n), (VIII- o), (Vlll-p), and (Vlll-q), and the names of the 6-deoxy saccharides from which they are derived.

Table 2:

^{7 7}

(Vlll-b) (Vlll-d) (Vlll-f) (Vlll-h)

O. O..

Cbs^ ^⁰ Y°~PG⁷ Cbs PG Cbs"' s^⁰ _' ⁰~~PG⁷ Cbs-^{^} ^°\/⁰^pG⁷

PG^_QIJ _Q-PG⁸ PG^' PG PG^{1 l} _nJ\J"_n-PG⁸ PG¹^n \/ n_^PG⁸

6. O O'

6 ₉ O g O g

'PG 'PG 'PG 'PG

(Vlll-i) (Vlll-k) (Vlll-n) (Vlll-p)

O H ,

ll-n) 3C

(Vl ^u C H ₃ (Vlll-n-a)

Cbs =

Scheme 5: Carbaborane synthons of formulae (Vlll-a), (Vlll-b), (Vlll-c), (Vlll-d), (Vlll-e), (VIII- f), (Vlll-g), (Vlll-h), (Vlll-i), (Vlll-j), (Vlll-k), (Vlll-m), (Vlll-n), (Vlll-o), (Vlll-p), (Vlll-q), and (Vlll- n-a).

Finally, the compounds of the present invention can be obtained by simultaneous cleavage of the conjugates, illustrated by formulae (IX) and (XI) in combination with Scheme 6c, from the amide resin and removal of protecting groups still present, e.g. protecting groups blocking functional groups attached to the amino acid side chains (i.e. removal of PG¹, PG², PG⁴, PG⁵ and/or PG⁶) and the saccharide based Sac moiety (i.e. to convert Sac’ into Sac) attached to the carbaborane, by removal of PG⁷, PG⁸, PG⁹, and PG¹⁰, as illustrated by Schemes 6a and 6b, using methods known to the person skilled in the art, e.g. using trifluoroacetic acid mixed with a trialkyl silane of the formula (Ci-C₄-alkyl)₃-SiH, preferably triisopropylsilane, and/or further optional reagents such as an organic thiol, preferably 1 ,2-ethanedithiol, an organic thioether, preferably thioanisol, and/or water, more preferably using a 90:10 v/v trifluoroacetic acid/triisopropylsilane mixture, to obtain compounds of the present invention, as illustrated by formulae (X) and (XII), in which R¹, X¹, X², L-His, X³, L-Arg, X⁴, X⁵, r and Sac are as defined for the general formula (I) (hence both formulae (X) and (XII) constitute sub-compartments of the general formula (I)), in combination with Scheme 6d. This reaction may proceed with concomitant mutarotation reactions in the saccharide based Sac moiety, as discussed supra, giving rise to the respective isomers, and/or mixtures thereof. Subsequent to said cleavage reaction, the compounds of the invention can be isolated by work-up and purification using methods well known to the person skilled in the art, such as precipitation with a suitable solvent such as diethyl ether, optionally used as mixture with an aliphatic hydrocarbon such as hexane, dissolution in an aqueous solvent mixture such as aqueous acetonitrile, followed by lyophilisation and purification e.g. by preparative reversed-phase HPLC. Specific examples are described in the Experimental Section.

Scheme 6a: Attachment of a carbaborane synthon of formula (VIII), i.e. a synthon selected from the formulae (Vlll-a) to (Vlll-q), to the amino group of the C-terminal L-amino acid, such as the e-amino group of the side chain of a C-terminal L-lysine, in a resin-bonded intermediate of formula (IV), followed by cleavage from the amide resin and deprotection.

Scheme 6b: Attachment of two equivalents of a carbaborane synthon of formula (VIII), i.e. a synthon selected from the formulae (Vlll-a) to (Vlll-q), to the free amino groups of a (2S)-2,3- diaminopropionic acid branching group attached to a resin-bonded intermediate as shown in formula (VII), followed by cleavage from the amide resin and deprotection.

Scheme 6c: List of Sac’ groups referred to i Schemes 6a and 6b.

Scheme 6d: List of Sac groups referred to i Schemes 6a and 6b. Availability of starting materials and carbaborane synthons

Amide resins for automated peptide synthesis, and suitably protected amino acids and protected DAABM branching moiety synthons such as Dap are well known to the person skilled in the art and are also commercially available in considerable variety. Several carbaborane synthons suitable for coupling to peptides are known to the person skilled in the art (see e.g. Ahrens et al., J. Med. Chem. 2011 , 54, 2368-2377; Frank et al., Polyhedron, 2012, 39, 9-13; for a more general overview see: Grimes, Russel N.: Carboranes. Third Edition, Academic Press (Elsevier), 2016; ISBN: 9780128018941 ), some are also described in the Experimental section (see paragraph on Intermediates for Reference Examples).

Carbaborane synthons suitable for the preparation of the compounds of the present invention, i.e. 9-(carboxymethylthio)-1 ,7-dicarba-c/oso-dodecaborane(12) derivatives conjugated to a protected group Sac’ of formula (VIII), as referred to in Schemes 6a and 6b, and as shown in more detail in Scheme 5, can be prepared according to Scheme 7a, below, from 9-(mercapto)- 1 ,7-dicarba-c/oso-dodecaborane(12) (formula (XIII)), the preparation of which is well known (see e.g. Zakharkin and Pisareva, Phosphorus and Sulfur and Rel. Bern. 1984, 20, 357). Said 9- (mercapto)-l ,7-dicarba-c/oso-dodecaborane(12) can be reacted with tert- butanol in the 6-fold volume of TFA in dichloromethane as a solvent, to give 9-(fe/f-butylthio)-1 ,7-dicarba-c/oso- dodecaborane(12) (formula (XIV), which in turn can be reacted with a saccharide based synthon Sac’-LG of the general formula (XV), which is selected from the formulae (XV-a), (XV-b), (Xl-c), (XV-d), (XV-e), (XV-f), (XV-g), (XV-h), (XV-i), (XV-j), (XV-k), (XV-m), (XV-n), (XV-o), (XV-p), and (XV-q) shown below in Scheme 7b, in which LG represents a leaving group as defined supra, preferably [(trifluoromethyl)sulfonyl]oxy, and in which PG⁷, PG⁸, PG⁹, and PG¹⁰ represent protecting groups suitable for the protection of hydroxy groups on saccharides, such as benzyl or acetyl, and in which preferably two groups selected from PG⁷, PG⁸, PG⁹, and PG¹⁰ attached to hydroxy groups on adjacent carbon atoms together form the group -C(CH3)2-. Particularly, said saccharide based synthon Sac’-LG is 1 ,2:3,4-di-0-isopropylidene-6-deoxy-a-D- galactopyranosyl-6-triflate (formula (XV-n-a; CAS 71001 -09-7), in which PG⁷ and PG⁸ together form -C(CH₃)2-; PG⁹ and PG¹⁰ together form -C(CH3)2-; LG represents [(trifluoromethyl)sulfonyl]oxy, and which can be prepared e.g. according to Brackhagen et al., J. Carbohydrate Chem. 2001 , 20, 31 . Said reaction can yield fully protected carbaborane- saccharide conjugates of the formula (XVII). The tert- butyl group protecting the 9-mercapto group can then be removed by methods known to the person skilled in the art, e.g. using mercury(ll)acetate in a solvent such as dichloromethane, followed by treatment with a mercaptoalcohol, preferably 2-mercaptoethanol, to give the corresponding protected monosaccaride conjugates of 9-(mercapto)-1 ,7-dicarba-c/oso-dodecaborane(12) of formula (XVII). The carboxymethylene group enabling peptide coupling is subsequently established by reacting the free mercapto group thus formed with iodoacetic acid (formula (XVIII), in the presence of a tertiary aliphatic amine, preferably triethylamine, in a solvent such as dichloromethane, to give carbaborane synthons of formula (VIII) featuring the 9- (carboxymethylthio)-1 ,7-dicarba-c/oso-dodecaborane(12) conjugated to a protected monosaccaride. Preferably, the saccharide is 6-deoxy-D-galactose. Specific examples are described in the Experimental Section.

Scheme 7a: Synthesis of the carbaborane synthons of formula (VIII) from 9-(mercapto)-1 ,7- dicarba-c/oso-dodecaborane(12) (formula (XIII)).

Scheme 7b: Saccharide based synthons Sac’-LG of formula (XV), which is selected from (XV- a), (XV-b), (XV-c), (XV-d), (XV-e), (XV-f), (XV-g), (XV-h), (XV-i), (XV-j), (XV-k), (XV-m), (XV-n), (XV-o), (XV-p), (XV-q), and (XV-n-a).

The compounds of general formula (I) of the present invention can be converted to any salt, preferably pharmaceutically acceptable salts, as described herein, by any method which is known to the person skilled in the art. Similarly, any salt of a compound of general formula (I) of the present invention can be converted into the free compound, by any method which is known to the person skilled in the art.

Compounds of general formula (I) of the present invention demonstrate a valuable pharmacological spectrum of action which could not have been predicted. Compounds of the present invention have surprisingly been found to effectively mediate activation of the human melanocortin 1 receptor, said activation resulting in internalization of the receptor, together with the compounds of the present invention bonded to it, into HEK293 cells transfected with the human melanocortin 1 receptor, as shown by data given in the biological experimental section. Compounds of the present invention can therefore be used to selectively transport boron atoms into cells expressing the human melanocortin 1 receptor, such as melanoma cells, to enable boron neutron capture therapy of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma.

Furthermore surprising, high levels of receptor activation and internalization into HEK293 cells transfected with the human melanocortin 1 receptor are maintained over a range of carbaborane loading, up to at least four carbaborane units per peptide unit, enabling for transferring a large number of boron atoms per cell into cells expressing the human melanocortin 1 receptor. So far, multiple carbaborane loading to receptor activating peptides has been known hitherto only for a completely different type of receptor, i.e. the human Yi receptor, to be compatible with high levels of receptor activation and internalization.

Reference Examples RE2 and RE9, in comparison to RE1 , demonstrate that attachment of Tam, used as fluorescence label in receptor internalization studies, does not impair human melanocortin 1 receptor activation regardless as to whether said Tam label is attached at the N- terminus or the C-terminus of NAPamide, and both Tam labelled peptides RE2 and RE9 were detected by intensive red fluorescence in the cytosol, indicating high uptake of RE2 and RE9 into HEK293 cells transfected with the human melanocortin 1 receptor independent from the point of attachment of the Tam fluorescence label.

Reference Examples RE3 and RE5 and Example 1 , as well as their Tam fluorescence labelled analogues RE4, RE10 and RE14, all featuring one carbaborane moiety (m1a for RE3 and RE4; m9b for RE5 and RE10; ml J9b for RE 14 and Example 1 ) conjugated to the NAPamide peptide backbone, all showed a level of human melanocortin 1 receptor activation comparable to RE2 and RE9. However, whilst RE10 and RE14 also showed comparable uptake into HEK293 cells transfected with the human melanocortin 1 receptor, said uptake was found to be decreased for RE4, indicating that said uptake is depending on the specific carbaborane moiety. Reference Examples RE5, RE6 and RE7, as well as their Tam fluorescence labelled analogues RE10, RE11 and RE12, featuring one, two, or four carbaborane m9b moieties (one for RE5 and RE10; two for RE6 and RE11 ; four for RE7 and RE12) conjugated to the NAPamide backbone, showed decreasing levels of human melanocortin 1 receptor activation with increasing numbers of carbaborane moieties per peptide unit. Likewise, RE10, RE11 and RE12, showed decreasing levels of uptake into HEK293 cells transfected with the human melanocortin 1 receptor, indicating carbaborane loading limitations for said uptake in case the carbaborane m9b moiety is used for carbaborane loading. However, said receptor activation and said uptake were, albeit decreased, still well detectable for RE12, and, regarding said receptor activation, also for RE7.

Reference Examples RE8 and its Tam fluorescence labelled analogue RE13, featuring also four carbaborane units conjugated to the NAPamide backbone, however in this instance attached as the carbaborane bm9x moiety featuring two carbaborane units per moiety, did neither show any measurable level of human melanocortin 1 receptor activation, nor any measurable uptake into HEK293 cells transfected with the human melanocortin 1 receptor, demonstrating that the structure of the carbaborane moiety has a substantial impact on the properties of the resulting conjugates with NAPamide regarding said receptor activation and said uptake.

On the other hand, the example compounds of the present invention, namely Examples 1 , 2 and 3, as well as their Tam fluorescence labelled analogues RE14, RE15 and RE16, featuring one, two, or four carbaborane m1J9b moieties (one for Example 1 and RE14; two for Example 2 and RE15; four for Example 3 and RE16) conjugated to the NAPamide backbone, showed a level of human melanocortin 1 receptor activation comparable to RE2 and RE9, and even an increased uptake into HEK293 cells transfected with the human melanocortin 1 receptor as compared to RE9, regardless whether one, two or four carbaborane m1 J9b moieties were attached to the peptide backbone of the conjugates.

As to date multiple carbaborane loading has been disclosed in the prior art only for carbaborane- peptide conjugates substantially differing in the structure of the peptide to which the carbaboranes are attached, and which address a completely different receptor ( i.e . the human Yi receptor), the fact that compounds of the present invention featuring saccharide functionalised carbaborane moieties, as exemplified by examples 1 to 3, maintain high levels of human melanocortin 1 receptor activation and uptake into HEK293 cells transfected with the human melanocortin 1 receptor up to a loading of at least four carbaborane units per NAPamide peptide unit, could indeed not be predicted by the person skilled in the art. The results obtained with the reference examples featuring carbaborane moieties other then ml J9b disclosed herein underline the importance of the specific structure of the carbaborane moiety, that is in particular the saccharide functionalisation, for the surprising and advantageous properties of the compounds of the present invention. It is possible therefore that said compounds can be used for the treatment or prophylaxis of diseases, preferably cancer in humans and animals.

Compounds of the present invention can be utilised to selectively transport boron atoms into cells expressing the melanocortin 1 receptor, such as cancer cells, to enable boron neutron capture therapy of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma. Boron neutron capture therapy of cancer comprises (i.) the step of accumulating a drug containing non-radioactive boron, preferably its ¹⁰B isotope, inside tumour cells, and (ii.). local irradiation of the tumour with thermal or epithermal neutrons. This method comprises administering to a mammal in need thereof, including a human, an amount of a compound of general formula (I) of the present invention, or an isomer resulting from a mutarotation reaction, a tautomer, an N-oxide, a hydrate, a solvate, or a salt thereof, or a mixture of same, which is effective to treat cancer.

Cancer includes, but is not limited to, for example: solid tumours, such as cancers of the breast, respiratory tract, brain, reproductive organs, digestive tract, urinary tract, eye, liver, skin, head and neck, thyroid, parathyroid, cancers of the adrenal gland and related tumours, and their distant metastases. Cancer also includes lymphomas, sarcomas, and leukaemias.

Examples of breast cancers include, but are not limited to, breast carcinoma, such as invasive ductal carcinoma, invasive lobular carcinoma, ductal carcinoma in situ, and lobular carcinoma in situ.

Examples of cancers of the respiratory tract include, but are not limited to, small-cell and non- small-cell lung carcinoma, as well as bronchial adenoma and pleuropulmonary blastoma.

Examples of brain cancers include, but are not limited to, brain stem and hypophtalmic glioma, cerebellar and cerebral astrocytoma, medulloblastoma, ependymoma, as well as neuroectodermal and pineal tumour.

Tumours of the male reproductive organs include, but are not limited to, prostate and testicular cancer.

Tumours of the female reproductive organs include, but are not limited to, endometrial, cervical, ovarian, vaginal, and vulvar cancer, as well as sarcoma of the uterus.

Tumours of the digestive tract include, but are not limited to, anal, colon, colorectal, oesophageal, gallbladder, gastric, pancreatic, rectal, small-intestine, and salivary gland cancers.

Tumours of the urinary tract include, but are not limited to, bladder, penile, kidney, such as renal cell carcinoma, further renal pelvis, ureter, urethral and human papillary renal cancers.

Eye cancers include, but are not limited to, intraocular melanoma and retinoblastoma. Examples of liver cancers include, but are not limited to, hepatocellular carcinoma (liver cell carcinomas with or without fibrolamellar variant), cholangiocarcinoma (intrahepatic bile duct carcinoma), and mixed hepatocellular cholangiocarcinoma.

Skin cancers include, but are not limited to, squamous cell carcinoma, Kaposi’s sarcoma, malignant melanoma, Merkel cell skin cancer, and non-melanoma skin cancer.

Head-and-neck cancers include, but are not limited to, laryngeal, hypopharyngeal, nasopharyngeal, oropharyngeal cancer, lip and oral cavity cancer and squamous cell.

Examples of adrenal gland and related tumours include, but are not limited to, adrenocortical adenoma, adrenocortical carcinoma, neuroblastoma and pheochromocytoma.

Lymphomas include, but are not limited to, AIDS-related lymphoma, non-Hodgkin’s lymphoma, cutaneous T-cell lymphoma, Burkitt lymphoma, Hodgkin’s disease, and lymphoma of the central nervous system.

Sarcomas include, but are not limited to, sarcoma of the soft tissue, osteosarcoma, malignant fibrous histiocytoma, lymphosarcoma, and rhabdomyosarcoma.

Leukemias include, but are not limited to, acute myeloid leukemia, acute lymphoblastic leukemia, chronic lymphocytic leukemia, chronic myelogenous leukemia, and hairy cell leukemia.

These disorders have been well characterized in humans, but also exist with a similar etiology in other mammals, and can be treated by administering pharmaceutical compositions of the present invention.

Generally, the use of chemotherapeutic agents and/or anti-cancer agents in combination with a compound or pharmaceutical composition of the present invention will serve to:

1. yield better efficacy in reducing the growth of a tumour or even eliminate the tumour as compared to administration of either agent alone,

2. provide for the administration of lesser amounts of the administered chemotherapeutic agents,

3. provide for a chemotherapeutic treatment that is well tolerated in the patient with fewer deleterious pharmacological complications than observed with single agent chemotherapies and certain other combined therapies,

4. provide for treating a broader spectrum of different cancer types in mammals, especially humans,

5. provide for a higher response rate among treated patients, 6. provide for a longer survival time among treated patients compared to standard chemotherapy treatments,

7. provide a longer time for tumour progression, and/or

8. yield efficacy and tolerability results at least as good as those of the agents used alone, compared to known instances where other cancer agent combinations produce antagonistic effects.

In other embodiments of the present invention, the compounds of general formula (I) of the present invention can be used advantageously in combination with local irradiation of the tumour with thermal or epithermal neutrons, optionally in combination with surgical intervention.

In other embodiments, the present invention also provides a method of killing a cell, wherein a cell is administered one or more compounds of the present invention in combination with irradiation with thermal or epithermal neutrons.

In other embodiments of the present invention, a cell is killed by treating the cell by irradiation with thermal or epithermal neutrons after treating a cell with one or more compounds of general formula (I) of the present invention to sensitize the cell to cell death, the cell is treated by irradiation with thermal or epithermal neutrons to kill the cell.

In one aspect of the invention, a compound of general formula (I) of the present invention is administered to a cell prior to the irradiation with thermal or epithermal neutrons.

In another aspect, the cell is in vitro. In another embodiment, the cell is in vivo.

The term“treating” or“treatment” as used in the present text is used conventionally, e.g., the management or care of a subject for the purpose of combating, alleviating, reducing, relieving, improving the condition of a disease or disorder, such as cancer.

The compounds of the present invention can be used in particular in therapy and prevention, i.e. prophylaxis, of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma.

Further, the compounds of the present invention can be used in combination with irradiation with thermal or epithermal neutrons in particular in therapy and prevention, i.e. prophylaxis, of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma.

In accordance with a further aspect, the present invention covers compounds of general formula (I), as described supra, or isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, particularly pharmaceutically acceptable salts thereof, or mixtures of same, for use in the treatment or prophylaxis of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma.

In accordance with a further aspect, the present invention covers compounds of general formula (I), as described supra, or isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, particularly pharmaceutically acceptable salts thereof, or mixtures of same, for use in the treatment or prophylaxis of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma, in combination with irradiation with thermal or epithermal neutrons.

The pharmaceutical activity of the compounds according to the present invention can be explained by their affinity to, and activation of human melanocortin 1 receptors, their internalization into cells expressing human melanocortin 1 receptors upon receptor activation, resulting in the selective transport of a large number of boron atoms into said cells, followed by the release of linear high energy transfer particles (alpha particles (⁴He²⁺ nuclei) and lithium-7 nuclei) upon local irradiation with thermal or epithermal neutrons.

In accordance with a further aspect, the present invention covers the use of compounds of general formula (I), as described supra, or isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, particularly pharmaceutically acceptable salts thereof, or mixtures of same, for the treatment or prophylaxis of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma.

In accordance with a further aspect, the present invention covers the use of a compound of general formula (I), as described supra, or an isomer resulting from a mutarotation reaction, a tautomer, an N-oxide, a hydrate, a solvate, or a salt thereof, particularly a pharmaceutically acceptable salt thereof, or a mixture of same, for the prophylaxis or treatment of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma.

In accordance with a further aspect, the present invention covers the use of compounds of general formula (I), as described supra, or isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, particularly pharmaceutically acceptable salts thereof, or mixtures of same, in a method of treatment or prophylaxis of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma.

In accordance with a further aspect, the present invention covers the use of a compound of general formula (I), as described supra, or isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, particularly pharmaceutically acceptable salts thereof, or mixtures of same, for the preparation of a pharmaceutical composition, preferably a medicament, for the prophylaxis or treatment of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma.

In accordance with a further aspect, the present invention covers a method of treatment or prophylaxis of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma, using an effective amount of a compound of general formula (I), as described supra, or isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, particularly pharmaceutically acceptable salts thereof, or mixtures of same.

In accordance with a further aspect, the present invention covers the use of compounds of general formula (I), as described supra, or isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, particularly pharmaceutically acceptable salts thereof, or mixtures of same, in combination with irradiation with thermal or epithermal neutrons, for the treatment or prophylaxis of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma.

In accordance with a further aspect, the present invention covers the use of a compound of formula (I), described supra, or an isomer resulting from a mutarotation reaction, a tautomer, an N-oxide, a hydrate, a solvate, or a salt thereof, particularly a pharmaceutically acceptable salt thereof, or a mixture of same, in combination with irradiation with thermal or epithermal neutrons, for the prophylaxis or treatment of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma.

In accordance with a further aspect, the present invention covers the use of compounds of general formula (I), as described supra, or isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, particularly pharmaceutically acceptable salts thereof, or mixtures of same, in combination with irradiation with thermal or epithermal neutrons, in a method of treatment or prophylaxis of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma.

In accordance with a further aspect, the present invention covers use of a compound of general formula (I), as described supra, or isomers resulting from mutarotation reactions, tautomers, N- oxides, hydrates, solvates, and salts thereof, particularly pharmaceutically acceptable salts thereof, or mixtures of same, for the preparation of a pharmaceutical composition, preferably a medicament, for the prophylaxis or treatment of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma, in combination with irradiation with thermal or epithermal neutrons. In accordance with a further aspect, the present invention covers a method of treatment or prophylaxis of diseases, in particular cancer, such as skin cancer, particularly melanoma, more particularly malignant melanoma, using an effective amount of a compound of general formula (I), as described supra, or isomers resulting from mutarotation reactions, tautomers, N-oxides, hydrates, solvates, and salts thereof, particularly pharmaceutically acceptable salts thereof, or mixtures of same, in combination with irradiation with thermal or epithermal neutrons.

In accordance with a further aspect, the present invention covers pharmaceutical compositions, in particular a medicament, comprising a compound of general formula (I), as described supra, or an isomer resulting from a mutarotation reaction, a tautomer, an N-oxide, a hydrate, a solvate, a salt thereof, particularly a pharmaceutically acceptable salt, or a mixture of same, and one or more excipients), in particular one or more pharmaceutically acceptable excipient(s). Conventional procedures for preparing such pharmaceutical compositions in appropriate dosage forms can be utilized.

The present invention furthermore covers pharmaceutical compositions, in particular medicaments, which comprise at least one compound according to the invention, conventionally together with one or more pharmaceutically suitable excipients, and to their use for the above mentioned purposes.

It is possible for the compounds according to the invention to have systemic and/or local activity. For this purpose, they can be administered in a suitable manner, such as, for example, via the oral, parenteral, pulmonary, nasal, sublingual, lingual, buccal, rectal, vaginal, dermal, transdermal, conjunctival, otic route or as an implant or stent.

For these administration routes, it is possible for the compounds according to the invention to be administered in suitable administration forms.

For oral administration, it is possible to formulate the compounds according to the invention to dosage forms known in the art that deliver the compounds of the invention rapidly and/or in a modified manner, such as, for example, tablets (uncoated or coated tablets, for example with enteric or controlled release coatings that dissolve with a delay or are insoluble), orally- disintegrating tablets, films/wafers, films/lyophylisates, capsules (for example hard or soft gelatine capsules), sugar-coated tablets, granules, pellets, powders, emulsions, suspensions, aerosols or solutions. It is possible to incorporate the compounds according to the invention in crystalline and/or amorphised and/or dissolved form into said dosage forms.

Parenteral administration can be effected with avoidance of an absorption step (for example intravenous, intraarterial, intracardial, intraspinal or intralumbal) or with inclusion of absorption (for example intramuscular, subcutaneous, intracutaneous, percutaneous or intraperitoneal). Administration forms which are suitable for parenteral administration are, inter alia, preparations for injection and infusion in the form of solutions, suspensions, emulsions, lyophylisates or sterile powders.

Examples which are suitable for other administration routes are pharmaceutical forms for inhalation [inter alia powder inhalers, nebulizers], nasal drops, nasal solutions, nasal sprays; tablets/films/wafers/capsules for lingual, sublingual or buccal administration; suppositories; eye drops, eye ointments, eye baths, ocular inserts, ear drops, ear sprays, ear powders, ear-rinses, ear tampons; vaginal capsules, aqueous suspensions (lotions, mixturae agitandae), lipophilic suspensions, emulsions, ointments, creams, transdermal therapeutic systems (such as, for example, patches), milk, pastes, foams, dusting powders, implants or stents.

The compounds according to the invention can be incorporated into the stated administration forms. This can be effected in a manner known per se by mixing with pharmaceutically suitable excipients. Pharmaceutically suitable excipients include, inter alia,

• fillers and carriers (for example cellulose, microcrystalline cellulose (such as, for example, Avicel^®), lactose, mannitol, starch, calcium phosphate (such as, for example, Di-Cafos^®)),

• ointment bases (for example petroleum jelly, paraffins, triglycerides, waxes, wool wax, wool wax alcohols, lanolin, hydrophilic ointment, polyethylene glycols),

• bases for suppositories (for example polyethylene glycols, cacao butter, hard fat),

• solvents (for example water, ethanol, isopropanol, glycerol, propylene glycol, medium chain-length triglycerides fatty oils, liquid polyethylene glycols, paraffins),

• surfactants, emulsifiers, dispersants or wetters (for example sodium dodecyl sulfate), lecithin, phospholipids, fatty alcohols (such as, for example, Lanette^®), sorbitan fatty acid esters (such as, for example, Span^®), polyoxyethylene sorbitan fatty acid esters (such as, for example, Tween^®), polyoxyethylene fatty acid glycerides (such as, for example, Cremophor^®), polyoxethylene fatty acid esters, polyoxyethylene fatty alcohol ethers, glycerol fatty acid esters, poloxamers (such as, for example, Pluronic^®),

• buffers, acids and bases (for example phosphates, carbonates, citric acid, acetic acid, hydrochloric acid, sodium hydroxide solution, ammonium carbonate, trometamol, triethanolamine),

• isotonicity agents (for example glucose, sodium chloride),

• adsorbents (for example highly-disperse silicas),

• viscosity-increasing agents, gel formers, thickeners and/or binders (for example polyvinylpyrrolidone, methylcellulose, hydroxypropylmethylcellulose, hydroxypropyl- cellulose, carboxymethylcellulose-sodium, starch, carbomers, polyacrylic acids (such as, for example, Carbopol^®); alginates, gelatine),

• disintegrants (for example modified starch, carboxymethylcellulose-sodium, sodium starch glycolate (such as, for example, Explotab^®), cross- linked polyvinylpyrrolidone, croscarmellose-sodium (such as, for example, AcDiSol^®)),

• flow regulators, lubricants, glidants and mould release agents (for example magnesium stearate, stearic acid, talc, highly-disperse silicas (such as, for example, Aerosil^®)),

• coating materials (for example sugar, shellac) and film formers for films or diffusion membranes which dissolve rapidly or in a modified manner (for example polyvinylpyrrolidones (such as, for example, Kollidon^®), polyvinyl alcohol, hydroxypropylmethylcellulose, hydroxypropylcellulose, ethylcellulose, hydroxypropyl- methylcellulose phthalate, cellulose acetate, cellulose acetate phthalate, polyacrylates, polymethacrylates such as, for example, Eudragit^®)),

• capsule materials (for example gelatine, hydroxypropylmethylcellulose),

• synthetic polymers (for example polylactides, polyglycolides, polyacrylates, polymethacrylates (such as, for example, Eudragit^®), polyvinylpyrrolidones (such as, for example, Kollidon^®), polyvinyl alcohols, polyvinyl acetates, polyethylene oxides, polyethylene glycols and their copolymers and blockcopolymers),

• plasticizers (for example polyethylene glycols, propylene glycol, glycerol, triacetine, triacetyl citrate, dibutyl phthalate),

• penetration enhancers,

• stabilisers (for example antioxidants such as, for example, ascorbic acid, ascorbyl palmitate, sodium ascorbate, butylhydroxyanisole, butylhydroxytoluene, propyl gallate),

• preservatives (for example parabens, sorbic acid, thiomersal, benzalkonium chloride, chlorhexidine acetate, sodium benzoate),

• colourants (for example inorganic pigments such as, for example, iron oxides, titanium dioxide),

• flavourings, sweeteners, flavour- and/or odour-masking agents.

The present invention furthermore relates to a pharmaceutical composition which comprises at least one compound according to the invention, conventionally together with one or more pharmaceutically suitable excipient(s), and to their use according to the present invention. In accordance with another aspect, the present invention covers pharmaceutical combinations, in particular medicaments, comprising at least one compound of general formula (I) of the present invention and at least one or more further active ingredients, in particular for the treatment and/or prophylaxis of cancer.

Particularly, the present invention covers a pharmaceutical combination, which comprises:

• one or more first active ingredients, in particular compounds of general formula (I) as defined supra, and

• one or more further active ingredients, in particular for the treatment and/or prophylaxis of cancer.

The term“combination” in the present invention is used as known to persons skilled in the art, it being possible for said combination to be a fixed combination, a non-fixed combination or a kit- of-parts.

A“fixed combination” in the present invention is used as known to persons skilled in the art and is defined as a combination wherein, for example, a first active ingredient, such as one or more compounds of general formula (I) of the present invention, and a further active ingredient are present together in one unit dosage or in one single entity. One example of a“fixed combination” is a pharmaceutical composition wherein a first active ingredient and a further active ingredient are present in admixture for simultaneous administration, such as in a formulation. Another example of a “fixed combination” is a pharmaceutical combination wherein a first active ingredient and a further active ingredient are present in one unit without being in admixture.

A non-fixed combination or“kit-of-parts” in the present invention is used as known to persons skilled in the art and is defined as a combination wherein a first active ingredient and a further active ingredient are present in more than one unit. One example of a non-fixed combination or kit-of-parts is a combination wherein the first active ingredient and the further active ingredient are present separately. It is possible for the components of the non-fixed combination or kit-of- parts to be administered separately, sequentially, simultaneously, concurrently or chronologically staggered.

The compounds of the present invention can be administered as the sole pharmaceutical agent or in combination with one or more other pharmaceutically active ingredients where the combination causes no unacceptable adverse effects. The present invention also covers such pharmaceutical combinations. For example, the compounds of the present invention can be combined with known agents for the treatment and/or prophylaxis of cancer.

Examples of agents for the treatment and/or prophylaxis of cancer include:

131 1-chTNT, abarelix, abiraterone, aclarubicin, adalimumab, ado-trastuzumab emtansine, afatinib, aflibercept, aldesleukin, alectinib, alemtuzumab, alendronic acid, alitretinoin, altretamine, amifostine, aminoglutethimide, hexyl aminolevulinate, amrubicin, amsacrine, anastrozole, ancestim, anethole dithiolethione, anetumab ravtansine, angiotensin II, antithrombin III, aprepitant, arcitumomab, arglabin, arsenic trioxide, asparaginase, atezolizumab, axitinib, azacitidine, basiliximab, belotecan, bendamustine, besilesomab, belinostat, bevacizumab, bexarotene, bicalutamide, bisantrene, bleomycin, blinatumomab, bortezomib, buserelin, bosutinib, brentuximab vedotin, busulfan, cabazitaxel, cabozantinib, calcitonine, calcium folinate, calcium levofolinate, capecitabine, capromab, carbamazepine carboplatin, carboquone, carfilzomib, carmofur, carmustine, catumaxomab, celecoxib, celmoleukin, ceritinib, cetuximab, chlorambucil, chlormadinone, chlormethine, cidofovir, cinacalcet, cisplatin, cladribine, clodronic acid, clofarabine, cobimetinib, copanlisib , crisantaspase, crizotinib, cyclophosphamide, cyproterone, cytarabine, dacarbazine, dactinomycin, daratumumab, darbepoetin alia, dabrafenib, dasatinib, daunorubicin, decitabine, degarelix, denileukin diftitox, denosumab, depreotide, deslorelin, dianhydrogalactitol, dexrazoxane, dibrospidium chloride, dianhydrogalactitol, diclofenac, dinutuximab, docetaxel, dolasetron, doxifluridine, doxorubicin, doxorubicin + estrone, dronabinol, eculizumab, edrecolomab, elliptinium acetate, elotuzumab, eltrombopag, endostatin, enocitabine, enzalutamide, epirubicin, epitiostanol, epoetin alfa, epoetin beta, epoetin zeta, eptaplatin, eribulin, erlotinib, esomeprazole, estradiol, estramustine, ethinylestradiol, etoposide, everolimus, exemestane, fadrozole, fentanyl, filgrastim, fluoxymesterone, floxuridine, fludarabine, fluorouracil, flutamide, folinic acid, formestane, fosaprepitant, fotemustine, fulvestrant, gadobutrol, gadoteridol, gadoteric acid meglumine, gadoversetamide, gadoxetic acid, gallium nitrate, ganirelix, gefitinib, gemcitabine, gemtuzumab, Glucarpidase, glutoxim, GM- CSF, goserelin, granisetron, granulocyte colony stimulating factor, histamine dihydrochloride, histrelin, hydroxycarbamide, 1-125 seeds, lansoprazole, ibandronic acid, ibritumomab tiuxetan, ibrutinib, idarubicin, ifosfamide, imatinib, imiquimod, improsulfan, indisetron, incadronic acid, ingenol mebutate, interferon alfa, interferon beta, interferon gamma, iobitridol, iobenguane (1231), iomeprol, ipilimumab, irinotecan, Itraconazole, ixabepilone, ixazomib, lanreotide, lansoprazole, lapatinib, lasocholine, lenalidomide, lenvatinib, lenograstim, lentinan, letrozole, leuprorelin, levamisole, levonorgestrel, levothyroxine sodium, lisuride, lobaplatin, lomustine, lonidamine, masoprocol, medroxyprogesterone, megestrol, melarsoprol, melphalan, mepitiostane, mercaptopurine, mesna, methadone, methotrexate, methoxsalen, methylaminolevulinate, methylprednisolone, methyltestosterone, metirosine, mifamurtide, miltefosine, miriplatin, mitobronitol, mitoguazone, mitolactol, mitomycin, mitotane, mitoxantrone, mogamulizumab, molgramostim, mopidamol, morphine hydrochloride, morphine sulfate, nabilone, nabiximols, nafarelin, naloxone + pentazocine, naltrexone, nartograstim, necitumumab, nedaplatin, nelarabine, neridronic acid, netupitant/palonosetron, nivolumab, pentetreotide, nilotinib, nilutamide, nimorazole, nimotuzumab, nimustine, nintedanib, nitracrine, nivolumab, obinutuzumab, octreotide, ofatumumab, olaparib, olaratumab, omacetaxine mepesuccinate, omeprazole, ondansetron, oprelvekin, orgotein, orilotimod, osimertinib, oxaliplatin, oxycodone, oxymetholone, ozogamicine, p53 gene therapy, paclitaxel, palbociclib, palifermin, palladium-103 seed, palonosetron, pamidronic acid, panitumumab, panobinostat, pantoprazole, pazopanib, pegaspargase, PEG-epoetin beta (methoxy PEG-epoetin beta), pembrolizumab, pegfilgrastim, peginterferon alfa-2b, pembrolizumab, pemetrexed, pentazocine, pentostatin, peplomycin, Perflubutane, perfosfamide, Pertuzumab, picibanil, pilocarpine, pirarubicin, pixantrone, plerixafor, plicamycin, poliglusam, polyestradiol phosphate, polyvinylpyrrolidone + sodium hyaluronate, polysaccharide-K, pomalidomide, ponatinib, porfimer sodium, pralatrexate, prednimustine, prednisone, procarbazine, procodazole, propranolol, quinagolide, rabeprazole, racotumomab, radium-223 chloride, radotinib, raloxifene, raltitrexed, ramosetron, ramucirumab, ranimustine, rasburicase, razoxane, refametinib , regorafenib, risedronic acid, rhenium-186 etidronate, rituximab, rolapitant, romidepsin, romiplostim, romurtide, rucaparib, samarium (153Sm) lexidronam, sargramostim, satumomab, secretin, siltuximab, sipuleucel-T, sizofiran, sobuzoxane, sodium glycididazole, sonidegib, sorafenib, stanozolol, streptozocin, sunitinib, talaporfin, talimogene laherparepvec, tamibarotene, tamoxifen, tapentadol, tasonermin, teceleukin, technetium (99mTc) nofetumomab merpentan, 99mTc-HYNIC-[Tyr3]-octreotide, tegafur, tegafur + gimeracil + oteracil, temoporfin, temozolomide, temsirolimus, teniposide, testosterone, tetrofosmin, thalidomide, thiotepa, thymalfasin, thyrotropin alfa, tioguanine, tocilizumab, topotecan, toremifene, tositumomab, trabectedin, trametinib, tramadol, trastuzumab, trastuzumab emtansine, treosulfan, tretinoin, trifluridine + tipiracil, trilostane, triptorelin, trametinib, trofosfamide, thrombopoietin, tryptophan, ubenimex, valatinib, valrubicin, vandetanib, vapreotide, vemurafenib, vinblastine, vincristine, vindesine, vinflunine, vinorelbine, vismodegib, vorinostat, vorozole, yttrium-90 glass microspheres, zinostatin, zinostatin stimalamer, zoledronic acid, zorubicin.

Based upon standard laboratory techniques known to evaluate compounds useful for the treatment of cancer, by standard toxicity tests and by standard pharmacological assays for the determination of treatment of the cancer related conditions identified above in mammals, and by comparison of these results with the results of known active ingredients or medicaments that are used to treat these conditions, the effective dosage of the compounds of the present invention can readily be determined for treatment of each desired indication. The amount of the active ingredient to be administered in the treatment of one of these conditions can vary widely according to such considerations as the particular compound and dosage unit employed, the mode of administration, the period of treatment, the age and sex of the patient treated, and the nature and extent of the condition treated.

The total amount of the active ingredient to be administered will generally range from about 0.001 mg/kg to about 200 mg/kg body weight per day, and preferably from about 0.01 mg/kg to about 20 mg/kg body weight per day. Clinically useful dosing schedules will range from one to three times a day dosing to once every four weeks dosing. In addition, it is possible for "drug holidays", in which a patient is not dosed with a drug for a certain period of time, to be beneficial to the overall balance between pharmacological effect and tolerability. It is possible for a unit dosage to contain from about 0.5 mg to about 1500 mg of active ingredient, and can be administered one or more times per day or less than once a day. The average daily dosage for administration by injection, including intravenous, intramuscular, subcutaneous and parenteral injections, and use of infusion techniques will preferably be from 0.01 to 200 mg/kg of total body weight. The average daily rectal dosage regimen will preferably be from 0.01 to 200 mg/kg of total body weight. The average daily vaginal dosage regimen will preferably be from 0.01 to 200 mg/kg of total body weight. The average daily topical dosage regimen will preferably be from 0.1 to 200 mg administered between one to four times daily. The transdermal concentration will preferably be that required to maintain a daily dose of from 0.01 to 200 mg/kg. The average daily inhalation dosage regimen will preferably be from 0.01 to 100 mg/kg of total body weight.

Of course the specific initial and continuing dosage regimen for each patient will vary according to the nature and severity of the condition as determined by the attending diagnostician, the activity of the specific compound employed, the age and general condition of the patient, time of administration, route of administration, rate of excretion of the drug, drug combinations, and the like. The desired mode of treatment and number of doses of a compound of the present invention or a pharmaceutically acceptable salt or ester or composition thereof can be ascertained by those skilled in the art using conventional treatment tests.

EXPERIMENTAL SECTION

Nomenclature of carbaboranes has been used according to:

Nomenclature of Inorganic Chemistry: Recommendations 1990. International Union of Pure and Applied Chemistry, ed. Geoffrey J Leigh. Blackwell Scientific Publications, Oxford 1990, 228- 231 ; ISBN 0-632-02494-I.

The following table 3 lists the abbreviations used herein as far as they are not explained within the text body. Other abbreviations have their meanings customary per se to the skilled person.

Table 3: Abbreviations

The following table lists the abbreviations used herein.

Structures of protecting groups listed herein, such as Boc, Bom, Bum, Dde, Doc, Hoc, MIS, Mmt, Mpe, Mtr, Mts, Mtt, Pbf, 2-Ph'Pr, TBDMS, tBu, TEGBn, Tos, and Trt are shown (together with amino acids to which they are bonded) in table 1c, supra. For the structure of the Fmoc group see Scheme 4, supra.

The various aspects of the invention described in this application are illustrated by the following examples which are not meant to limit the invention in any way.

The example testing experiments described herein serve to illustrate the present invention and the invention is not limited to the examples given.

EXPERIMENTAL SECTION - GENERAL PART

All reagents, for which the synthesis is not described in the experimental part, are either commercially available, or are known compounds or may be formed from known compounds by known methods by a person skilled in the art.

The compounds and intermediates produced according to the methods of the invention may require purification. Purification of organic compounds is well known to the person skilled in the art and there may be several ways of purifying the same compound. In some cases, no purification may be necessary. In some cases, the compounds may be purified by crystallization. In some cases, impurities may be removed by trituration using a suitable solvent. In some cases, the compounds may be purified by chromatography, particularly flash column chromatography, using for example loose silica or silica gel in glass columns, with manual or automated fraction collecting, or using prepacked silica gel cartridges, e.g. Biotage SNAP cartidges KP-Sil^® or KP- NH^® in combination with an automated column chromatography device such as a Biotage autopurifier system (SP4^® or Isolera Four^®), and eluents such as gradients of hexane/ethyl acetate or DCM/methanol. In some cases, the compounds may be purified by preparative HPLC using commercially available HPLC equipment, for example a Waters autopurifier equipped with a diode array detector and/or on-line electrospray ionization mass spectrometer in combination with a suitable prepacked reverse phase column and eluents such as gradients of water and acetonitrile which may contain additives such as trifluoroacetic acid, formic acid or aqueous ammonia. Eluents can be removed by methods known to the person skilled in the art, such as lyophilisation.

In some cases, purification methods as described above can provide those compounds of the present invention which possess a sufficiently basic or acidic functionality in the form of a salt, such as, in the case of a compound of the present invention which is sufficiently basic, a trifluoroacetate or formate salt for example, or, in the case of a compound of the present invention which is sufficiently acidic, an ammonium salt for example. A salt of this type can either be transformed into its free base or free acid form, respectively, by various methods known to the person skilled in the art, or be used as salts in subsequent biological assays. It is to be understood that the specific form (e.g. salt, free base etc.) of a compound of the present invention as isolated and as described herein is not necessarily the only form in which said compound can be applied to a biological assay in order to quantify the specific biological activity.

HPLC methods

Analytical methods are summarised in context of Tables 6a, 6b and 6c, infra. Further analytical and preparative HPLC methods are described in the protocols within the Experimental Section.

NMR spectra NMR measurements were carried out on a Bruker AVANCE III HD spectrometer with an Ascend™ 400 magnet. Tetramethylsilane was used as internal standard, and ¹¹B-NMR spectra were referenced to the X scale (see: R. K. Harris, E. D. Becker, S. M. Cabral de Menezes, R. Goodfellow, P. Granger, NMR nomenclature. Nuclear spin properties and conventions for chemical shifts (IUPAC Recommendations 2001 ). Pure Appl. Chem. 73, 1795 (2001 )). All chemical shifts are reported in ppm. Assignment of the ¹H and ¹³C signals was based on 2D NMR spectra (H,H-COSY, HMQC, HSQC, HMBC). Identification of the boron atom attached to sulfur was possible by comparison of the proton-coupled and -decoupled ¹¹B-NMR spectra.

On the following pages, some NMR signals that appear as broad overlapping signals with the shape of a multiplet in either ¹H-, ¹¹B{¹H}-, ¹¹B-, ¹⁰B{¹H}- or ¹⁰B-NMR spectra are just described as‘br’ (broad). In this case, the superscript a is added (br³).

Example of a ¹H-NMR spectrum: the rectangle marks the region of interest

O = B atom

• = BH group

Example of a -NMR spectrum: the rectangle marks the region of interest

O = B atom

• = BH group

Example of a ¹¹B-NMR spectrum: the rectangle marks the region of interest

O = B atom

• = BH group

Example of a -NMR spectrum: the rectangle marks the region of interest

O = B atom

• = BH group

Example of a ¹⁰B-NMR spectrum: the rectangle marks the region of interest

O = B atom

• = BH group

Elemental analysis

All obtained elemental analysis data (carbon, nitrogen, hydrogen) were performed with a Heraeus VARIO EL device.

Infrared spectra

IR data were obtained with a Perkin-Elmer FT-IR spectrometer Spectrum 2000 on KBr pellets and on a Thermo Scientific Nicolet iS5 with an ATR unit in the range from 4000 to 400 cm ¹. All detected signals were interpreted as weak ( w ), medium ( m ) or strong (s).

Mass spectra

EI-LR mass spectra were obtained on a Finnigan MAT 8230 from Finnigan MAT (now: Thermo Fisher Scientific). ESI-LR mass spectra were obtained on a Bruker Daltonics Esquire 3000plus (ESI-lon Trap LC MSMS) and ESI-HR mass spectra were obtained on a Bruker Daltonics IMPACT II. Isotopic pattern simulations were performed with Bruker Compass Data Analysis 4.2 SR1 (version 4.2, copyright 2014, Bruker Daltonic GmbH). Formic acid was sometimes added for better ionisation of the carbaborane-containing compounds. Only the most intense peak of the isotopic pattern of each species is listed for the low and high resolution mass spectra.

X-Ray crystallography

The X-ray measurements were carried out on a Gemini-S CCD diffractometer (Agilent Technologies) with Mok_a radiation and w scan rotation (data reduction with CrysAlis Pro, Oxford Diffraction Ltd., Oxfordshire, UK, 2010) empirical absorption correction with SCALE3 ABSPACK (Oxford Diffraction Ltd., Oxfordshire, UK, 2010). The collected data were processed and refined by using WinGX (see L. J. Farrugia, WinGX suite for small-molecule single-crystal crystallography, J. Appl. Crystallogr. 32, 837 (1999)) including the programs SIR92 (see A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, Completion and refinement of crystal structures with SIR 92, J. Appl. Crystallogr. 26, 343 (1993)) and SHELX97 (see G. M. Sheldrich, SHELXL97: program for the refinement of crystal structures, Universitat Gottingen, Gottingen, Germany, 1997) . All hydrogen atoms were refined independently. Images of the molecular structures were generated with ORTEP (see L. J. Farrugia, ORTEP-3 for Windows - a version of ORTEP-III with a Graphical User Interface (GUI), J. Appl. Crystallogr. 1997, 30, 565; Diamond Crystal and Molecular Structure Visualization;: Crystal Impact, Dr. H. Putz & Dr. K. Brandenburg GbR, Kreuzherrenstr. 102, D-53227 Bonn, Germany).

EXPERIMENTAL SECTION - GENERAL PROCEDURES Peptide Synthesis

Materials

Fmoc-protected amino acids were obtained from Orpegen OPC (Heidelberg, Germany) and Iris Biotech (Marktredwitz, Germany). EDT and thioanisole were from Fluka (Buchs, Switzerland); HOBt, DIC, Oxyma and poly-D-lysine hydrobromide were obtained from Iris Biotech. Tam was from emp Biotech GmbH (Berlin, Germany). Glycylglycin was purchased from AppliChem GmbH (Darmstadt, Germany). ACN was obtained from VWR (Darmstadt, Germany), DMF and DCM from Biosolve (Valkenswaard, The Netherlands). Diethyl ether and ethanol were obtained from Scharlau (Barcelona, Spain). AC2O, DMSO, DIPEA, forskolin, HATU, Hoechst33342, hydrazine, NaCI, piperidine, TFA, TIS and DBU were purchased from Sigma-Aldrich (Taufkirchen, Germany). Cell culture media (Dulbecco’s Modified Eagle’s Medium (DMEM), Ham’s F12), as well as trypsin-EDTA, Dulbecco’s Phosphate-Buffered Saline (DPBS), and Hank’s Balanced Salt Solution (HBSS) were obtained from Lonza (Basel, Switzerland). Fetal calf serum (FCS) was from Biochrom GmbH (Berlin, Germany). Hygromycin B was purchased from Invivogen (Toulouse, France) and Opti-MEM was obtained from Life Technologies (Basel, Switzerland). EcoRV, Bsp1407, Xhol and T4-DNA ligase were purchased from Thermo Scientific (Waltham, MA, USA). Lipofectamine™ 2000 was obtained from Invitrogen (Carlsbad, CA, USA). MetafectenePro™ was received from Biontex Laboratories GmbH (Munchen, Germany). Rink amide resin was purchased from Novabiochem (Merck KGaA, Darmstadt, Germany). ONE-Glo Luciferase Assay System™ was purchased from Promega (Madison, Wl, USA). n-Hexan was from Grussing GmbH (Filsum, Germany).

General Information and methods for peptide synthesis

All NAPamide analogs were synthesized on a Rink amide resin with an automated peptide synthesizer (SYRO I, MultiSynTech). Each N_a-Fmoc-protected amino acid with side chain protecting groups (Asp(tBu), His(Trt), Arg(Pbf), Trp(Boc) and Lys(Boc), if not indicated otherwise) and the reagents Oxyma and DIC were added in 8-fold molar excess (120 pmol) in DMF. The reaction was carried out for 40 min. The Fmoc protecting group was cleaved with 40 % piperidine in DMF ( vlv ) for 3 min and 20 % piperidine in DMF ( vlv ) for 10 min after each coupling step. Every reaction was performed twice and was finished with Fmoc deprotection before starting the next reaction cycle. All reactions and procedures were performed at room temperature. After each coupling and deprotection step, the resins were washed with solvent to remove excess of reagents. Peptides coupled to Tam were protected from light. Kaiser Test and sample cleavage with analytics were carried out when deemed necessary. Analytics were performed using RP-HPLC with linear gradients of ACN (0.08 % TFA) in FhO (0.1 % TFA) and mass spectrometry. Monoisotopic mass was investigated by MALDI-ToF MS and average mass by ESI-iontrap MS, if not indicated otherwise. Preparative RP-HPLC with linear gradients of ACN (0.08 % TFA) in H₂0 (0.1 % TFA) was applied for peptide purification.

EXPERIMENTAL SECTION - INTERMEDIATES

The following reactions were carried out using the Schlenk technique well known to the person skilled in the art and dry nitrogen gas as an inert gas.

Intermediate 1 : 9-(Mercapto)-1 -dicarba-c/oso-dodecaborane(12)

(CAS 64493-44-3)

O = B ato m

• = BH group

The title compound was prepared according to L. I. Zakharkin, I. V. Pisareva, Phosphorus and Sulfur and Rel. Elem. 20, 357 (1984); see compound 3.

Yield: 8.64 g (49.0 mmol, 71 %)

¹H-NMR (400 MHz, CDCIs): d = 0.47 (m, 1 H, SH), 1 .44 - 3.41 (br³, m, 9H, BI₀H₉), 2.98 (br s, 2H, CH) ppm.

¹¹B{¹H}-NMR (128 MHz, CDCIs): d = -2.6 (s, 1 B), -5.8 (s, 2B), -8.9 (s, 1 B), -12.5 (s, 2B), -13.8 (s, 2B), -17.6 (s, 1 B), -20.8 (s, 1 B) ppm.

Syntheses of Intermediates for Reference Examples

Intermediate 2: 1 -(Carboxy)-1 -dicarba-c/oso-dodecaborane

(Carbaborane m1a synthon; CAS18581 -81 -2)

O = B ato m

• = BH group

The title compound was prepared from m-carbaborane (CAS-Nr.: 16986-24-6; Katchem spol. s r. o., Elisky Krasnohorske 123/6, 1 10 00 Josefov, Czech Republic) according to R. A. Kasar,

G. M. Knudsen, S. B. Kahl, Inorg. Chem. 38, 2936 (1999).

Yield: 0.6 g (3.1 mmol, 90%)

¹H-NMR (400 MHz, CDCIs): d = 1.50 - 3.20 (br³, 10H, B₁₀H₁₀), 3.02 (s, 1 H, C¹H), 8.94 (br, s,

1 H, C³OOH) ppm.

¹¹B{¹H}-NMR (128 MHz, CDCI₃): d = -15.7 (s, 2B), -13.2 (s, 2B), -1 1.3 (s, 2B), -10.6 (s, 2B), -6.5 (s, 1 B), -4.9 (s, 1 B) ppm.

Intermediate 3: 9-(Carboxymethylthio)-1 -dicarba-c/oso-dodecaborane(12) (Carbaborane m9b synthon; CAS 74555-68-3 )

O = B atom

• = BH group 0.97 g (5.50 mmol, 1.0 eq.) 9-(mercapto)-1 ,7-dicarba-c/oso-dodecaborane(12) (see Intermediate 1 ) and 1.02 g (5.50 mmol, 1.0 eq.) iodoacetic acid were dissolved in 20 ml acetonitrile. 5.74 ml (4.26 g, 33.02 mmol, 6.0 eq.) of diisopropylethylamine were added in one portion at ambient temperature. The mixture was stirred at ambient temperature for 3 days. The reaction was stopped by the addition of aqueous 2 N hydrochloric acid. The organic solvent was removed under reduced pressure and the aqueous phase was diluted with 75 ml distilled water and extracted three times with 150 ml DCM. The combined organic phases were dried over sodium sulfate and after filtration the solvent was removed under reduced pressure. The raw product was purified by column chromatography on silica using n- hexane/ethyl acetate ( v/v ) as eluent followed by recrystallisation in n-hexane yielding 0.72 g (3.07 mmol, 56%) of the title compound as a white solid.

¹H-NMR (400 MHz, CDCIs): d = 1.30 - 3.50 (br³, 9H, B_I0H₉), 3.0 (br, s, 2H, 2xC³H), 3.40 (m, 2H, C²H₂), 10.5 (br, s, 1 H, C¹OOH) ppm

1⁰B{¹H}-NMR (43 MHz, CDCIs): d = -0.5 (1 B), -6.4 (2B), -9.8 (1 B), -13.1 (2B), -13.7 (2B), -

17.4 (1 B), -20.0 (1 B) ppm

¹³C{¹H}-NMR (100 MHz, CDCIs): d = 34.5 (C²H₂), 54.4 (2xC³H), 174.6 (C¹OOH) ppm

IR spectroscopy (KBr, v in cm ¹): 3436 (m), 3059 (s), 2916 (w), 2608 (s), 1698 (s), 1433 (s), 1390 (w), 1305 (s), 1205 (s), 1 162 (m), 1069 (w), 993 (m), 951 (m), 915 (m), 891 (m), 871 (m),

794 (w), 775 (w), 760 (w), 731 (w), 670 (w), 454 (w).

Intermediate 4: 2-Chloro-4,6-bis(1 ,7-dicarba-c/oso-dodecaboran-9-ylthio)-1 ,3,5- triazine

5.00 g (28.4 mmol, 2.00 eq.) 9-(mercapto)-1 ,7-dicarba-c/oso-dodecaborane(12) (see Intermediate 1 ) and 2.62 g (14.2 mmol, 1.00 eq.) cyanuric chloride were placed in an evacuated and nitrogen-purged 500 ml. two-neck round-bottom flask, equipped with a condenser. The starting materials were suspended in 200 ml. acetonitrile and cooled to 0 °C. 6.04 ml. (4.59 g, 35.5. mmol, 2.50 eq.) diisopropylethylamine were added slowly to this suspension. After 20 minutes stirring at 0 °C the mixture was heated to reflux. After five hours of heating the reaction mixture was cooled to room temperature and stirred overnight at ambient temperature. The reaction was stopped by adding 20 ml. water and 20 mL 2 M aqueous hydrochloric acid. Excess acetonitrile was removed under reduced pressure and the remaining aqueous phase was extracted three times with 30 mL ethyl acetate. The combined organic phases were washed with 20 mL of a saturated aqueous sodium chloride solution and 20 mL water, respectively. Both aqueous washing solutions were extracted with 50 mL diethyl ether. All combined organic phases were dried over magnesium sulfate, filtered and then the solvent was removed under reduced pressure. The purity of the obtained material proved to be sufficient (by TLC (ethyl acetate/n-hexane, 1 :2, v/v). The title compound was isolated as a slightly yellow solid (quantitative yield, 6.59 g, 14.2 mmol, R _f = 0.63).

¹H-NMR (400 MHz, (CD₃)₂CO): d = 1.52 - 3.54 (br³, 18H, 2XBI₀H₉S), 3.82 (br, s, 4H, 4xC¹H) ppm.

¹¹B{¹H}-NMR (128 MHz, (CD₃)₂CO): d = -18.1 (br, s, 2B), -16.8 (s, 2B), -13.8 (s, 4B), -12.8 (br³, 4B), -10.4 (s, 2B), -5.9 (br, s, 4B), -4.0 (s, 2B, 2xBS) ppm.

¹¹B-NMR (128 MHz, (CD₃)₂CO): d = -17.5 (br³, 4B), -13.2 (br³ 8B), -10.4 (d, ¹J_BH = 152 Hz, 2B), -5.9 (d, ¹ JBH = 165 Hz, 4B), -4.0 (s, 2B, 2xBS) ppm.

¹³C{¹H}-NMR (100 MHz, (CD₃)₂CO): d = 56.1 (br, s, 4xC¹H), 168.5 (s, C_q ³CI), 182.6 (s, 2xC_q ²S) ppm.

IR spectroscopy (KBr, v in cm^-1): 3446 (m), 3072 (m), 3060 (m), 3050 (m), 2962 (w), 2617 (s), 2390 (w), 2091 (w), 1988 (w), 1718 (w), 1624 (w), 1562 (w), 1501 (s), 1477 (s), 1456 (s), 1432 (m), 1312 (m), 1274 (s), 1252 (s), 1 166 (m), 1 150 (m), 1 105 (w), 1067 (m), 1036 (w), 992 (m), 954 (m), 920 (w), 863 (s), 846 (s), 806 (m), 790 (m), 773 (m), 760 (m), 732 (m), 676 (w), 624 (w), 576 (w), 507 (w), 376 (w).

Mass spectrometry (LR-ESI, positive mode, CH₂CI₂/CH₃CN):

calculated for C₇H₂₃B₂oChN₃S₂: m/z = 465.1 ([M+H]⁺) found: m/z = 465.4 ([M+H]⁺)

calculated for C14H46B40CI2UN6S4: m/z = 935.1 (100%, [2M+Li]⁺) found: m/z = 935.6 (100%, [2M+Li]⁺)

Mass spectrometry (LR-ESI, negative mode, CH2CI2/CH₃CN):

calculated for C7H23B20CI2N3S2: m/z = 499.5 ([M+CI] )

found: m/z = 499.3 ([M+CI] )

Elemental analysis:

calculated (%) for C7H22B20CI1N3S2: C = 18.12, H = 4.78;

found: C = 18.1 1 , H = 4.60.

Crystallographic data

Empirical formula C7H22B20CI1 N3S2

Formula weight 464.04

Temperature 130(2) K

Wavelength 71.073 pm

Crystal system Monoclinic

Space group P2i/c

Unit cell dimensions a = 1352.87(4) pm a = 90°

b = 141 1.68(4) pm b = 98.178(3)° c = 1249.64(5) pm Y = 90°

Volume 2.3623(1 ) nm³

Z 4

Density (calculated) 1 .305 Mg/m³

Absorption coefficient 0.343 mm ¹

F(000) 936

Crystal size 0.5 x 0.04 x 0.04 mm³

Theta range for data collection 2.19 to 30.75°

Index ranges -19 £ h < 19, -20 < k < 19,

Reflections collected 30792

Independent reflections 6750 [R(int) = 0.0598] Completeness to theta = 28.29° 100.0%

Absorption correction Semi-empirical from equivalents

Max. and min. transmission 1 and 0.96054

Refinement method Full-matrix least-squares on F²

Data / restraints / parameters 6750 / 0 / 388

Goodness-of-fit on F² 1.045

Final R indices [l>2sigma(l)] R1 = 0.0486, wR2 = 0.0879

R indices (all data) R1 = 0.0800, wR2 = 0.0975

Extinction coefficient n/a

Largest diff. peak and hole 0.315 and -0.305 e A-³

Comments: Structure solution with SHELXS-2013 (Direct method). Anisotropic refinement of all non-hydrogen atoms with SHELXL-2014. All H atoms were located on difference Fourier maps calculated at the final stage of the structure refinement. With a displacement parameter and bond length analysis the carbaborane carbon atoms C(1 ), C(2), C(3) and C(4) could clearly be localised.

Hydrogen atoms are omitted for clarity. Intermediate 5: A/⁶-r4,6-Bis(1 -dicarba-c/oso-dodecaboran-9-ylthio)-1,3,5-triazin- 2-yl1-A/²-(terf-butoxycarbonyl)-L-lvsine (Carbaborane bm9x synthon)

In an evacuated and nitrogen-purged 100 mL round-bottom flask 0.20 g (0.43 mmol, 1 .00 eq.) 2-chloro-4,6-bis(1 ,7-dicarba-c/oso-dodecaboran-9-ylthio)-1 ,3,5-triazine (see Intermediate 4) and 0.12 g (0.49 mmol, 1 .14 eq.) /V_a-(fe/f-butoxycarbonyl)-L-lysine were placed and suspended in a mixture of 20 mL acetonitrile and 25 mL water. To this mixture 0.07 g (1 .75 mmol, 4.07 eq.) of sodium hydroxide were added and stirred for 30 minutes at ambient temperature. Then the mixture was heated to reflux and stirred for 18 hours. The reaction process was monitored via TLC (ethyl acetate/n-hexane, 1 :1 , v/v). The reaction was stopped by adding 1 M aqueous hydrochloric acid until acidic pH. The precipitate which was formed was filtered off immediately and was washed with water to neutral pH. After column chromatography of the precipitate (acetone/n-hexane, 1 :1 , v/v, 2.5% glacial acetic acid) 138 mg (0.20 mmol, 46.5%, R _t = 0.65) of the title compound was isolated as a white solid.

¹H-NMR (400 MHz, CD₃CN): d = 1 .40 (s, 9H, C(C¹⁴H₃)₃), 1 .50 - 3.30 (br³, 18H, 2XBI₀H₉), 1 .59 (br, m, 4H, 2xCH₂, C⁶'⁷H₂), 1.77 (br, m, 2H, CH₂, C⁸H₂), 3.38 (br, s, 4H, 4xCⁱ H), 3.41 (m, 2H, C⁵H₂), 4.04 (m, 1 H, C⁹H), 5.54 (d, ³JHH = 7.8 Hz, 1 H, N¹¹H), 6.20 (m, 1 H, N⁴H), 9.50 (s, 1 H,

C¹⁰OOH) ppm.

¹¹B{¹H}-NMR (128 MHz, CD₃CN): d = -18.4 (s, 2B), -17.0 (s, 2B), -14.1 (s, 4B), -12.9 (s, 4B), -10.6 (s, 2B), -6.0 (s, 4B), -3.5 (s, 2B, 2xBS) ppm.

¹¹B-NMR (128 MHz, CD₃CN): d = -18.4 (br³, 2B), -17.0 (br, d, ¹J_BH = 192 Hz, 2B), -13.5 (br³, 8B), -10.6 (d, ¹ JBH = 154 Hz, 2B), -6.0 (d, ¹J_BH = 166 Hz, 4B), -3.5 (s, 2B, 2xBS) ppm. ¹³C{¹H}-NMR (100 MHz, CD₃CN): d = 23.9 (s, C^{6 or 7}H₂), 28.6 (s, C(C¹⁴H₃)₃), 30.2 (s, C^{6 or 7}H₂), 32.1 (s, C⁸H₂), 41.2 (s, C⁵H₂), 54.4 (s, C⁹H), 55.9 (br, s, 2xC^{1 or 1'}H), 56.0 (br, s, 2xC^{1 or 1'}H), 79.9 (s, C_q ¹³(CH₃)₃), 156.7 (s, 2xC_q ²S), 174.5 (s, C_q ³), 178.5 (s, C_q ¹²0), 179.6 (s, C_q ¹⁰O) ppm.

IR spectroscopy (KBr, v in cm^-1): 3856 (w), 3455 (m), 3258 (m), 3138 (m), 3058 (m), 2980 (m), 2934 (m), 2864 (m), 2603 (s), 1698 (s), 1614 (s), 1569 (m), 1520 (s), 1500 (s), 1452 (m), 1435

(m), 1410 (s), 1369 (s), 1307 (m), 12477 (s), 1218 (m), 1201 (m), 1 166 (s), 11 17 (m), 1059 (m), 1022 (w), 994 (w), 954 (m), 863 (s), 850 (s), 801 (m), 760 (m), 731 (m), 668 (w), 642 (w), 590 (w), 418 (w).

Mass spectrometry (HR-ESI, negative mode, CHCI₃/CH₃CN):

calculated for C_I3H₄₂B_2ON₅0₄S₂: m/z = 673.46669 ([M-H] )

found: m/z = 673.46701 ([M-H] )

Elemental analysis:

calculated (%) for C_I3H₄₃B_2ON₅0₄S₂: C = 32.08, H = 6.43, N = 10.39; found:

C = 31.17, H = 6.35, N = 10.11.

Syntheses of Intermediates for Example Compounds of the present invention

Intermediate 6: 9-(terf-Butylthio)-1 ,7-dicarba-c/oso-dodecaborane(12)

The following procedure was performed in analogy to the known synthesis of the analogous orf/70-carbaborane derivative (see R. Frank, S. Boehnke, A. Aliev, E. Hey-Hawkins, Polyhedron 39, 9 (2012).

3.00 g (17.02 mmol, 1.0 eq.) 9-(mercapto)-1 ,7-dicarba-c/oso-dodecaborane(12) (see Intermediate 1 ) were suspended in 140 ml fBuOH/TFA = 1/6 (v/v) and DCM was added dropwise until the mixture turned into a clear solution. The solution was kept at ambient temperature without stirring for 8 days during which a red-brown solution was formed. The reaction was stopped by the addition of an aqueous solution of sodium carbonate at 0 °C. Afterwards, the solution was diluted with 600 ml distilled water and sodium hydroxide was added until pH = 12 was reached. The aqueous phase was extracted three times with 300 ml DCM. The combined organic phases were dried over sodium sulfate, filtered and then the solvent was evaporated under reduced pressure giving 4.50 g of a yellow-brown oil, which crystallised over time. The raw product was purified by several recrystallisation steps in methanol yielding 2.93 g (12.55 mmol, 74% yield) of the title compound as pale yellow crystals.

¹H-NMR (400 MHz, CDCI₃): d = 1.45 (s, 9H, C(C³H₃)₃), 1.7 - 3.5 (br³, 9H, B_I0H₉), 2.95 (br, s, 2H, 2xC¹H) ppm.

1¹B{¹H}-NMR (128 MHz, CDCI₃): d = -1.0 (br, 1 B, BS), -6.3 (br, 2B), -9.6 (br, 1 B),—13.0 (br,

2B), -14.0 (br, 2B), -17.7 (br, 1 B), -20.1 (br, 1 B) ppm.

¹¹B-NMR (128 MHz, CDCI₃): d = -1.0 (br, s, 1 B, BS), -6.3 (d, ¹J_BH = 165 Hz, 2B), -9.6 (d, ¹ J_BH = 153 Hz, 1 B), -13.4 (m, 4B), -17.7 (d, ¹J_BH = 182 Hz, 1 B), -20.1 (d, ¹J_BH = 182 Hz, 1 B) ppm.

13 ¹H}-NMR (100 MHz, CDCIs): d = 32.7 (s, C(C³H₃)₃), 44.4 (s, C_q ²), 53.9 (s, 2xC¹H) ppm.

Elemental analysis:

Calculated for C H B S: C = 31 .01 % H = 8.68%;

found: C = 32.15% H = 8.41 %

Intermediate 7: 1,2:3,4-Di-0-isopropylidene-6-deoxy-a-D-qalactopyranosyl-6- triflate (CAS 71001-09-7)

The title compound was prepared according to M. Brackhagen, H. Boye and C. Vogel, J. Carbohydrate Chem. 2001 , 20(1), 31 -43.

7.50 g (28.80 mmol, 1.0 eq.) 1 ,2:3,4-di-0-isopropylidene-a-D-galactopyranose (see M. Brackhagen, H. Boye and C. Vogel, J. Carbohydrate Chem. 2001 , 20(1), 31 -43) were mixed with 7.6 ml (6.98 g, 57.60 mmol, 2.0 eq.) dry 2,4,6-collidine. The mixture was dissolved in 300 ml dry

DCM. 7.7 ml (13.00 g, 46.08 mmol, 1.6 eq.) trifluoromethanesulfonic anhydride were added dropwise over 30 minutes at ambient temperature to this solution. The reaction mixture turned deep yellow during the addition. Over a stirring period of 4 hours at ambient temperature, the mixture turned orange. The reaction was stopped by pouring the mixture onto 300 ml of iced water. The phases were separated and the water phase was extracted two times with 100 ml chloroform. The combined organic phases were washed two times with 250 ml of an aqueous 17% solution of potassium bisulfate. The organic phase was washed two times with 200 ml of iced water, two times with 250 ml of a saturated aqueous solution of sodium bicarbonate, once with 300 ml iced water and finally once with 300 ml of a saturated aqueous solution of sodium chloride. The organic phase was dried over sodium sulfate. The solution was concentrated by reduced pressure. TLC showed the product at an R_f-value of R_f = 0.46 (n- hexane/ethyl acetate = 3/1 v/v). The crude product was purified by column chromatography over silica using an isocratic n-hexane/ethyl acetate = 3/1 mixture (v/v) as eluent, yielding 10.54 g (26.80 mmol, 93%) of the title compound as a yellow oil, which slowly solidified in the fridge.

¹H-NMR (400 MHz, CDCI₃): d = 1.34 (s, 3H, CH₃), 1.34 (s, 3H, CH₃), 1.45 (s, 3H, CH₃), 1.53 (s, 3H, CH₃), 4.12 (ddd, ³J_HH = 7.0 Hz, ³J_HH = 4.7 Hz, ³J_HH = 2.0 Hz, 1H, CH⁵), 4.25 (dd,

J_HH = 7.8 Hz, ³J_HH = 2.0 Hz, 1H, CH⁴), 4.36 (dd, ³J_HH = 5.0 Hz, J_HH = 2.6 Hz, 1 H, CH²), 4.55 - 4.68 (m, 3H, CH³, CH⁶ ₂), 5.54 (d, ³J_HH = 4.9 Hz, 1H, CH¹) ppm.

¹³C{¹H}-NMR (100 MHz, CDCI₃): d = 24.4 (s, C⁹'¹¹H₃), 24.8 (s, C⁹'¹¹H₃), 25.8 (s, C⁹'¹¹H₃), 25.9 (s, C⁹'¹¹H₃), 66.1 (s, C⁵H), 70.2 (s, C²H), 70.4 (s, C⁴H), 70.6 (s, C³H), 74.6 (s, C⁶H₂), 96.1 (s, C¹H), 109.1 (s, C⁸’¹⁰(CH₃)₂), 1 10.1 (s, C⁸’¹⁰(CH₃)₂), 1 18.6 (q, ¹J_CF = 320 Hz, C⁷F₃) ppm.

Intermediate 8: 1 - 0-disopropylidene-6^,-deoxy-a-D-qalactopyranos-6^,-

nΐΐ- 9-(te/ -butylthio)-1 -dicarba-c/oso-dodecaborane(12)

O = B atom

• = BH group

The following procedure was performed in analogy to the known synthesis of the analogous orf/70-carbaborane derivative (see R. Frank, S. Boehnke, A. Aliev, E. Hey-Hawkins, Polyhedron 39, 9 (2012)..

2.97 g (12.78 mmol, 1.0 eq.) 9-(fe/f-butylthio)-1 ,7-dicarba-c/oso-dodecaborane(12) (see Intermediate 6) was dissolved in 100 ml diethyl ether and cooled to 0 °C and 8.72 ml (1.45 M in n-hexane, 12.64 mmol, 0.9 eq.) n-butyllithium were added dropwise. The reaction was allowed to warm up to room temperature over 2 hours. The solution was cooled to 0 °C again and 5.00 g (12.7 mmol, 1.0 eq.) 1 ,2:3,4-di-0-isopropylidene-6-deoxy-a-D-galactopyranosyltriflate (see Intermediate 7), dissolved in 50 ml diethyl ether, were added dropwise. The reaction was allowed to warm up to ambient temperature and stirred overnight. Wet diethyl ether was added and then the solvent was removed under reduced pressure. The residue was purified by column chromatography (ethyl acetate/n-hexane 1 :3 v/v) yielding 3.62 g (7.67 mmol, 60% yield) of the title compound as a colourless highly viscous oil (R_f-value = 0.50, n- hexane/ethyl acetate = 3/1 v/v).

¹H-NMR (400 MHz, CDCI₃): d = 1 .30 (s, 3H, C¹²'^12'H₃), 1 .34 (s, 3H, C¹³'^13'H₃), 1 .41 (s, 3H, C¹²'^12'H₃), 1.43 (s, 9H, C(CH₃)₃), 1.50 - 3.50 (br³, 9H, BI₀H₉), 1 .59 (s, 3H, C¹³'^13'H₃), 2.15 (virtual d, ²J_HH = 15.9 Hz, 1 H, C⁴H₂), 2.34 (ddd, ²J_HH = 16.0 Hz, ³J_HH = 9.0 Hz, ³J_HH = 4.6 Hz, 1 H, C⁴H₂), 2.96 (br, s, 1 H, C¹⁴H), 3.77 (ddt, ³J_HH = 8.9 Hz, ³J_HH = 4.4 Hz, ³J_HH = 2.2 Hz, 1 H, C⁵H), 4.04 (virtual dd, ³ _HH = 7.8 Hz, J_HH = 1.6 Hz, 1 H, C⁷H), 4.28 (virtual dd, ³J_HH = 5.1 Hz, J_HH = 2.4 Hz,

1 H, C⁸H), 4.57 (virtual dd, ³J_HH = 7.9 Hz, J_HH = 2.2 Hz, 1 H, C⁶H), 5.52 (d, ³J_HH = 5.1 Hz, 1 H, C⁹H) ppm.

¹³C{¹H}-NMR (100 MHz, CDCI₃): d = 23.3, 23.9 and 24.9 (s, 4xCH₃ of C¹²H₃, C¹² H₃, C¹³H₃ and C¹³ H₃), 31.8 (s, C(CH₃)₃), 37.1 (s, C⁴H₂), 43.2 (C_q ²), 53.8 and 54.0 (s, C¹⁴H), 65.9 and 66.0 (s, C⁵H), 69.0 (s, C⁸H), 69.8 (s, C⁶H), 71 .5 (s, C_q ³), 72.0 (s, C⁷H), 95.5 (s, C⁹H), 108.1 (s, C_q ¹¹), 108.3 (s, C_q ¹⁰) ppm.

¹¹B{¹H}-NMR (128 MHz, CDCI₃): d = -1.4 (s, 1 B, B⁹S), -2.0 to 20.0 (br³, 9B) ppm.

¹¹B-NMR (128 MHz, CDCI₃): d = -1.4 (s, 1 B, B⁹S), -2.0 to 20.0 (br³, 9B) ppm.

IR spectroscopy (KBr, v in cm ¹): 2989 (s), 2601 (s, BH), 1457 (m), 1384 (s), 1258 (s), 1213 (s), 1 166 (s), 1071 (s), 1003 (s), 899 (m), 858 (m), 738 (m), 510 (m).

Mass spectrometry (HR-ESI, positive mode):

calculated for Ci₈H₃₈BioOsSi: m/z = 475.35254 (int. 100%, [M+H]⁺) found: m/z = 475.35275 (int. 100%, [M+H]⁺) found:

Calculated:

Generic Display Report

Intermediate 9: 1 - Di-0-isopropylidene-6^,-deoxy-a-D-qalactopyranos-6^,-

yl)-9-(mercapto)-1 -dicarba-c/oso-dodecaborane(12)

12

O = B atom

• = BH group

The following procedure was performed in analogy to the known synthesis for the analogous orf/70-carbaborane derivative (see R. Frank, S. Boehnke, A. Aliev, E. Hey-Hawkins, Polyhedron 39, 9 (2012).

0.36 g (0.76 mmol, 1.0 eq.) 1-(1 ',2':3',4'-di-0-isopropylidene-6'-deoxy-a-D-galactopyranos-6'- yl)-9-(ferf-butylthio)-1 ,7-dicarba-c/oso-dodecaborane(12) (see Intermediate 8) was dissolved in DCM, transferred to a Schlenk flask, dried in high vacuum, and then dissolved in 3.5 ml dry acetic acid. 0.36 g (1.14 mmol, 1.5 eq.) mercury(ll)acetate was added in one portion, resulting in a pale yellow colour of the reaction mixture. The reaction mixture was stirred at 50 °C for 3 hours, during which the colour turned intensely yellow. The reaction was stopped by the addition of 1.6 ml (1.78 g, 22.75 mmol, 20.0 eq.) 2-mercaptoethanol, resulting in a black-greyish precipitate. The suspension was diluted with 100 ml ethyl acetate. The organic phase was two times extracted with 100 ml of an aqueous 5% solution of sodium bicarbonate. The resulting aqueous phase was then four times extracted with ethyl acetate, 200 ml each. The combined organic phases were concentrated under reduced pressure and dried over sodium sulfate. After filtration, the solution was further concentrated under reduced pressure to give a suspension, which crystallised overnight. TLC showed the product with an R_f-value of R_f = 0.47 (n- hexane/ethyl acetate = 3/1 v/v) as an orange spot followed by 2-(acetylthio)ethyl acetate with an R_f-value of R_f = 0.45 as a yellow spot; both changed colour upon staining with a 10% solution of palladium(ll) chloride in methanol. The crude product was purified by column chromatography over silica using an n-hexane/ethyl acetate gradient mixture (3/1 :1/1 ) as eluent, yielding 0.30 g (0.73 mmol, 96%) product as an oily solid.

¹H-NMR (400 MHz, CDCI₃): d = 2.06 (s, 3H, CH₃COO), 2.36 (s, 3H, CH₃COS), 3.13 (t, J_HH = 6.5 Hz, 2H, CH₂S), 4.18 (t, J_HH = 6.5 Hz, 2H, CH₂0) ppm.

for comparison see: M. Liras et al., Polym. Chem., 2013, 4, 5751-5759.

12

O = B atom

• = BH group

¹H-NMR (400 MHz, CDCI₃): d = 0.43 (m, 1 H, SH), 1.30 (s, 3H, 1xCH₃, C¹¹H₃ or C^{11 '}H₃), 1.34 (s, 3H, 1 XCH₃, C¹²H₃ or C^12'H₃), 1.42 (s, 3H, 1xCH₃, C¹¹H₃ or C^11'H₃), 1.50 - 3.50 (br³, 9H, B₁₀H₉), 1.59 and 1.60 (s, 3H, 1xCH₃, C¹²H₃ or C^12'H₃), 2.15 (virtual dt, ²J_HH = 15.9 Hz, J_HH = 2.6 Hz, 1 H, C³H₂), 2.34 (ddd, ² J_HH = 15.9 Hz, ³ J_HH = 8.7 Hz, J_HH = 3.4 Hz, 1 H, C³H₂), 2.97 (br, s, 1 H, C¹H), 3.75 (ddt, ³ J_HH = 8.9 Hz, J_HH = 4.4 Hz, ⁴ J_HH = 2.2 Hz, 1 H, C⁴H), 4.03 (dd, ³ J_HH = 7.9 Hz, ⁴ JHH = 2.0 Hz, 1 H, C⁶H), 4.28 (ddd, ³ JHH = 5.1 Hz, ⁴ JHH = 2.5 Hz, ⁴ JHH = 0.8 Hz, 1 H, C⁷H), 4.57 (ddd, ³ JHH = 7.8 Hz, ⁴ JHH = 2.5 Hz, ⁴ JHH = 1.0 Hz, 1 H, C⁵H), 5.52 (d, ³ JHH = 5.1 Hz, 1 H, C⁸H) ppm.

¹³C{¹H}-NMR (100 MHz, CDCI₃): d = 24.4, 24.9, 25.8 and 25.9 (s, 4xCH₃: C¹¹H₃, C^11'H₃, C¹²H₃, C^12'H₃), 37.9 and 38.0 (s, both C³H₂), 54.8 (br, s, C¹H), 68.0 and 67.0 (s, both C⁴H), 70.0 (C⁷H), 70.8 (C⁵H), 73.05 and 73.07 (s, both C⁶H), 73.5 (br, s, C_q ²), 96.6 (s, C⁸H), 108.70 and 108.73 (s, both Cq¹⁰), 109.3 (s, both C_q ⁹) ppm.

¹¹B{¹H}-NMR (128 MHz, CDCIs): d = -2.6 (s, 1 B, B⁹S), -5.0 to -22.0 (br³, 9B) ppm.

¹¹B-NMR (128 MHz, CDCIs): d = -2.6 (s, 1 B, B⁹S), -5.0 to -22.0 (br³, 9B) ppm.

IR spectroscopy (KBr, v in cm^-1): 3446 (br, m), 3051 (m), 2990 (s), 2937 (m), 2600 (s, BH), 1456 (w), 1428 (w), 1384 (s), 1257 (m), 1213 (m), 1 166 (m), 1 107 (m), 1070 (s), 1003 (m), 899 (m), 856 (m), 758 (m), 668 (w), 509 (w).

Mass spectrometry (HR-ESI, positive mode):

calculated for C14H30B10O5S1 : m/z = 419.28960 (int. 100%, [M]+) found: m/z = 419.28976 (int. 100%, [M]⁺)

Elemental analysis:

Calculated for C14H₃₀B1₀O₅S1 : C = 40.18% H = 7.22%;

found: C = 39.35% H = 7.40%

Found:

Calculated:

Generic Display Report

Intermediate 10: l Di-O-isopropylidene-e'-deoxy-a-D-qalactopyranos-

6^,-yl)-9-(carboxymethylthio)-1 -dicarba-c/oso-dodecaborane(12) (Carbaborane m1J9b synthon)

O = B atom

• = BH group

The following procedure was performed in analogy to the known synthesis for the analogous orf/70-carbaborane derivative (see R. Frank, S. Boehnke, A. Aliev, E. Hey-Hawkins, Polyhedron 39, 9 (2012)..

0.20 g (0.48 mmol, 1.0 eq.) 1-(T,2':3',4'-Di-0-isopropylidene-6'-deoxy-a-D-galactopyranos-6'- yl)-9-(mercapto)-1 ,7-dicarba-c/oso-dodecaborane(12) (see Intermediate 9) was dissolved in DCM, transferred to a Schlenk flask and dried in high vacuum. 0.27 g (1.43 mmol, 3.0 eq.) iodoacetic acid was added and both compounds were dissolved in 7 ml dry DCM. With stirring, 0.46 ml (0.34 g, 3.33 mmol, 7.0 eq.) dry triethylamine was added in one portion at ambient temperature. The mixture was stirred at ambient temperature for 3 days. The reaction mixture was cooled to 0 °C, and the reaction was stopped by the addition of ca. 10 ml of aqueous 2 N hydrochloric acid and stirred for 30 seconds. The phases were separated and the aqueous phase was first extracted two times with 10 ml ethyl acetate each and then three times with 20 ml ethyl acetate each. The combined organic phases were dried over sodium sulfate at 0 °C. After filtration, the solution was dried under reduced pressure. The raw product was purified by column chromatography on silica using an n- hexane/ethyl acetate gradient mixture (1/1 :0/1 ) as eluent, yielding 0.1 1 g (0.24 mmol, 50%) of a white oily solid. ¹H-NMR (400 MHz, CDCI₃): d = 1.30 (s, 3H, 1xCH₃, C¹²H₃ or C^12'H₃), 1.34 (s, 3H, 1xCH₃, C¹³H₃ or C^13'H₃), 1.42 (s, 3H, 1xCH₃, C¹²H₃ or C^12'H₃), 1.50 - 3.50 (br³, 9H, B_I0H₉), 1.587 and 1.593 (s, 3H, 1 XCH₃, C¹³H₃ or C^13'H₃), 2.14 (virtual dt, ² _HH = 15.9 Hz, J_HH = 2.5 Hz, 1 H, C⁴H₂), 2.35 (ddd, ² J_HH = 16.1 Hz, J_HH = 9.2 Hz, J_HH = 2.0 Hz, 1 H, C⁴H₂), 2.99 (br, s, 1 H, C¹⁴H), 3.38 (d, J_HH = 5.2 Hz, 2H, C²H₂) 3.74 (m, 1 H, C⁵H), 4.03 (m, 1 H, C⁷H), 4.29 (virtual dd, ³ J_HH = 5.1 Hz, ⁴ J_HH = 2.5 Hz, 1 H, C⁸H), 4.58 (virtual dd, J_HH = 7.9 Hz, ⁴ J_HH = 2.4 Hz, 1 H, C⁶H), 5.53 (d, ³ _HH = 5.1 Hz, 1 H, C⁹H), 8.45 (br, s, 1 H, COOH) ppm.

¹³C{¹H}-NMR (100 MHz, CDCI₃): d = 24.4, 24.9, 25.85 and 25.93 (s, 4xCH₃: C¹²H₃, C^12'H₃, C¹³H₃, C^13'H₃), 34.5 (s, C²H₂), 38.0 (s, C⁴H₂), 54.4 (s, C¹⁴H), 67.0 (s, C⁵H), 70.0 (s, C⁸H), 70.9 (s, C⁶H), 73.1 (s, C⁷H), 73.2 (s, C_q ³), 96.6 (s, C⁹H), 108.7 and 108.8 (both C_q ¹¹), 109.4 (s, C_q ¹⁰), 174.2 (s,

C_q ¹) ppm.

¹¹B{¹H}-NMR (128 MHz, CDCI₃): d = -0.8 (s, 1 B, B⁹S), -2.0 to -20.0 (br³, 9B) ppm.

¹¹B-NMR (128 MHz, CDCI₃): d = -0.8 (s, 1 B, B⁹S), -2.0 to -20.0 (br³, 9B) ppm.

IR spectroscopy (KBr, v in cm ¹): 3053 (s), 2990 (s), 2936 (s), 2602 (s, BH), 1712 (s, COOH), 1457 (m), 1428 (m), 1385 (s), 1303 (m), 1259 (s), 1213 (s), 1166 (s), 1 142 (m), 1 107 (s), 1069

(s), 1003 (s), 955 (m), 919 (m), 898 (m), 855 (m), 802 (m), 774 (m), 740 (m), 668 (w), 645 (w), 534 (w), 509 (m), 460 (w).

Mass spectrometry (HR-ESI, positive mode):

calculated for Ci₆H₃₂BioNai0₇Si: m/z = 499.27728 (int. 100%,[M+Na]⁺)

found: m/z = 499.27684 (int. 100%, [M+Na]⁺)

Elemental analysis:

calculated for Ci₆H₃₂Bio0₇Si: C = 40.32% H = 6.77%;

found: C = 40.05% H = 6.67%

Found:

Generic Display Report

Calculated:

Generic Display Report

EXPERIMENTAL SECTION - REFERENCE EXAMPLES

Table 4: Codes and Sequences of Reference Examples

Reference Example RE1 : NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Boc), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with Ac₂0 and DIPEA in DCM for 15 min. After the peptide had been cleaved from the resin and side chains had been deprotected with TFA/TIS (90:10, v/V) for 3 h, the peptide was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ).

Purification was carried out on a preparative RP-HPLC column (Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm), to give the title compound of reference example RE1. A linear gradient of 10 % to 35 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 25 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. The peptide was synthesized on a 15 pmol scale and the yield was 9.0 mg (55 % of theory). Identity of the peptide was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C₅₂H₇₄N₁₆O₁₁ (monoisotopic mass: 1098.6 Da; average mass: 1099.2 Da). The observed masses were in correspondence to the calculated mass. Due to the low molecular weight of the compound, the ESI-MS was able to detect the isotope pattern of the compound. Therefore, the monoisotopic mass was used for signal identification. ESI lontrap: m/z = 1099.5 [M+H]⁺, 550.4 [M+2H]²⁺, 367.4 [M+3H]³⁺; MALDI-ToF: m/z = 1099.6 [M+H]⁺. Peptide purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Proteo 4 pm 90 A (C12, 250 x 4.6 mm) with linear gradient of 10 % to 50 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 30 min (flow rate: 1.00 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm, 100 A (250 x 4.6 mm) with linear gradient of 10 % to 50 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) showed purities >95 % with retention times of 20.2 min and 13.1 min, respectively. Reference Example RE2: Tam-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Boc), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was modified with 6- carboxytetramethylrhodamine (Tam) by reaction with 2 equiv of Tam, HATU and DIPEA in DMF, protected from light. After the peptide had been cleaved from the resin and side chains had been deprotected with TFA/TA/EDT (90:7:3, v/v/v) for 3 h, peptide was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ).

Purification was carried out on a preparative RP-HPLC column (Phenomenex Proteo 10 pm 90 A, C12, 250 x 21.2 mm) to give the title compound of reference example RE2. A linear gradient of 20 % to 55 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 35 min was applied. The flow rate was 10 mL/min, UV detection was measured at l = 220 nm. The peptide was synthesized on a 15 pmol scale and the yield was 7.2 mg (33 % of theory).

Identity of the Tam modified peptide was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap-MS (HCT, Bruker). The chemical formula is C₇₅H₉₂N₁₈O₁₄ (monoisotopic mass: 1468.7 Da; average mass: 1469.6 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1470.8 [M+H]⁺, 735.4 [M+2H]²⁺, 490.6 [M+3H]³⁺; MALDI- ToF: m/z = 1469.9 [M+H]⁺, 735.5 [M+2H]²⁺. Peptide purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Proteo 4 pm 90 A (C12, 250 x 4.6 mm) with linear gradient of 10 % to 50 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 30 min (flow rate: 1.00 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm 100 A (Biphenyl, 250 x 4.6 mm) with linear gradient of 10 % to 50 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) showed purities >95 % with retention times of 18.5 min and 18.5 min.

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with Ac₂0 and DIPEA in DCM for 15 min, followed by the cleavage of Dde with 3 % hydrazine in DMF, 10 x 10 min. Carbaborane m1 a synthon (see Intermediate 2) was coupled to the free e- amino group of the C-terminal lysine using 3 equiv of the carbaborane m1 a synthon, 2.9 equiv HATU and 6 equiv DI PEA in DMF overnight. After the conjugate had been cleaved from the resin and side chains had been deprotected with TFA/TA/EDT (90:7:3, v/v/v) for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (1 :3).

Purification was carried out on a preparative RP-HPLC column (Phenomenex Proteo 10 pm 90 A, C12, 250 x 21.2 mm) to give the title compound of reference example RE3. A linear gradient of 20 % to 55 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 35 min was applied. The flow rate was 10 mL/min, UV detection was measured at l = 220 nm. The conjugate was synthesized on a 15 pmol scale and the yield was 2.8 mg (15% of theory).

Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is 0₅₅H₈₄NI_QOI₂BI_O (monoisotopic mass: 1270.7 Da; average mass: 1269.5 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1270.8 [M+H]⁺, 635.9 [M+2H]²⁺; MALDI-ToF: m/z = 1271 .67 [M+H]⁺. Conjugate purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Proteo 4 pm 90 A (C12, 250 x 4.6 mm) with linear gradient of 20 % to 70 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 40 min (flow rate: 0.6 ml/min, l = 220 nm) and (2) Phenomenex Aeris 3.6 pm, 100 A (250 x 4.6 mm) with linear gradient of 20 % to 70 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 40 min (flow rate: 1.55 ml/min, l = 220 nm) showed purities >95 % with retention times of 25.4 min and 17.5 min, respectively.

Reference Example RE4: Tam-rK⁸ 1-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Mmt), corresponding to the sequence L^NDHfRWGK, 6-carboxytetramethylrhodamine (Tam) was coupled to the N-terminus of the resin-bonded peptide using twice 2 equiv of Tam, HATU and DIPEA in DMF for at least 3 h. Mmt was cleaved off with 1 % TFA and 5 % TIS in DCM, 1 1 x 1 min, and carbaborane m1 a synthon (see Intermediate 2) was coupled to the free e-amino group of the C- terminal lysine using 3 equiv of the carbaborane m1 a synthon, 2.9 equiv HATU and 6 equiv DIPEA in DMF twice for at least 3 h. After the conjugate had been cleaved from the resin and the side chains had been deprotected with TFA/TA/EDT (90:7:3, v/v/v) for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (1 :3).

Purification was carried out on preparative RP-HPLC column (Phenomenex Jupiter 5 pm 300 A, C18, 250 x 21.2 mm). A linear gradient of 35 % to 70 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 50 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. A second purification was done on a semi-preparative RP-HPLC column (Phenomenex Kinetex 5 pm 100 A, C18, 250 x 10 mm) to give the title compound of reference example RE4. A linear gradient of 35 % to 75 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 55 min was applied. The flow rate was 6 mL/min, UV detection was measured at l = 220 nm. The conjugate was synthesized on a 15 pmol scale and the yield was 1.2 mg (5 % of theory). Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Brukerj and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C₇₈H₁₀₂N₁₈O₁₅B₁₀ (monoisotopic mass: 1640.9 Da; average mass: 1639.9 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 821.0 [M+2H]²⁺, 547.6 [M+3H]³⁺; MALDI-ToF: m/z = 1641.8 [M+H]⁺, 820.9 [M+2H]²⁺. Conjugate purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Proteo 4 pm 90 A (C12, 250 x 4.6 mm) with linear gradient of 20 % to 70 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 40 min (flow rate: 0.6 ml/min, l = 220 nm) and (2) Phenomenex Kinetex 5 pm 100 A (C18, 250 x 4.6 mm) with linear gradient of 20 % to 70 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 40 min (flow rate: 1.55 ml/min, l = 220 nm) showed purities >95 % with retention times of 25.8 min and 20.7 min, respectively.

Reference Example RE5: rK⁸ 1-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with Ac₂0 and DIPEA in DCM for 15 min. The Dde protecting group was subsequently cleaved off with 3 % hydrazine in DMF for 10 x 10 min. The subsequent coupling of carbaborane m9b synthon (see Intermediate 3) to the free e-amino group of the C-terminal lysine was performed using 1.5 equiv of said carbaborane m9b synthon, 3 equiv DIC and 3 equiv HOBt in DMF overnight. After the conjugate had been cleaved from the resin and the side chains had been deprotected with TFA/TIS (90:10, v/v) for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ).

Purification was carried out on a preparative RP-HPLC column (Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm) to give the title compound of reference example RE5. A linear gradient of 20 % to 50 % ACN (0.08 % TFA) in FhO (0.1 % TFA) over 30 min was applied.

The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. The conjugate was synthesized on a 15 pmol scale and the yield was 7.2 mg (37 % of theory).

Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C56H86N16O12B10S1 (monoisotopic mass: 1316.7 Da; average mass: 1315.6 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1316.7 [M+H]⁺, 658.8 [M+2H]²⁺; MALDI-ToF: m/z = 1317.7 [M+H]⁺. Conjugate purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Jupiter Proteo 4 pm 90 A (C12, 250 x 4.6 mm) with linear gradient of 10 % to 50 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1.00 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm 100

A (Biphenyl, 250 x 4.6 mm) with linear gradient of 10 % to 50 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) showed purities >95 % with retention times of 22.7 min and 16.6 min, respectively.

Reference Example RE6: rK⁸((2S)-Dap(m9b)₂)1-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with AC₂0 and DIPEA in DCM for 15 min. The Dde protecting group was subsequently cleaved off with 3 % hydrazine in DMF for 10 x 10 min. Then, 3 equiv Fmoc-(2S)-Dap(Fmoc)-OH were coupled to the free e-amino group of the C-terminal lysine in the presence of 4 equiv DIC and 4 equiv HOBt in DMF to introduce a (2S)-Dap branching moiety. Subsequent Fmoc deprotection with 20 % piperidine in DMF was followed coupling of carbaborane m9b synthon (see Intermediate 3) with 3 equiv of said carbaborane m9b synthon, 6 equiv DIC and 6 equiv HOBt in DMF. After the conjugate had been cleaved from the resin and the side chains had been deprotected with TFA/TIS (90:10, v/v) for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ).

Purification was carried out on a preparative RP-HPLC column (Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm), to give the title compound of reference example RE6. A linear gradient of 25 % to 55 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 30 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. The conjugate was synthesized on a 15 pmol scale and the yield was 3.4 mg (14 % of theory). Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C63H104N18O14B20S2 (monoisotopic mass: 1620.9 Da; average mass: 1618.0 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1619.0 [M+H]⁺, 810.0 [M+2H]²⁺, 540.4 [M+3H]³⁺; MALDI-ToF: m/z = 1621 .9 [M+H]⁺. Conjugate purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Jupiter

Proteo 4 pm 90 A (C12, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1 .00 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm 100 A (Biphenyl, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) showed purities >95 % with retention times of 28.4 min and 23.2 min, respectively.

Reference Example RE7: rK⁸«2S)-Dap«2S)-Dap 1-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with AC₂0 and DIPEA in DCM for 15 min. The Dde protecting group was subsequently cleaved off with 3 % hydrazine in DMF for 10 x 10 min. Fmoc-(2S)-Dap(Fmoc)-OH (3 equiv), DIC (4 equiv) and HOBt (4 equiv) were used for (2S)-Dap coupling to the free e-amino group of the C-terminal lysine overnight. Subsequent Fmoc deprotection with 20 % piperidine in DMF was followed by overnight coupling of two further (2S)-Dap units to the two free amino groups of the previously attached (2S)-Dap branching moiety, for which Fmoc-(2S)-Dap(Fmoc)-OH (6 equiv), DIC (8 equiv) and HOBt (8 equiv) were dissolved in DMF and added to the resin-bonded peptide. After Fmoc deprotection with 20 % piperidine in DMF, coupling of the carbaborane m9b synthon to the in total four free amino groups of the previously attached (2S)-Dap branching moieties was carried out with 6 equiv carbaborane m9b synthon (see Intermediate 3), 12 equiv DIC and 12 equiv HOBt in DMF overnight. After the conjugate had been cleaved from the resin and the side chains had been deprotected with TFA/TIS (90:10, v/v) for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ).

Purification was carried out on a preparative RP-HPLC column (Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm) to give the title compound of reference example RE7. A linear gradient of 45 % to 85 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 40 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. The conjugate was synthesized on a 15 pmol scale and the yield was 0.7 mg (2 % of theory). Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C77Hi4oN₂₂Oi8B₄oS4 (monoisotopic mass: 2229.3 Da; average mass: 2222.8 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1 1 12.5 [M+2H]²⁺, 741 .9 [M+3H]³⁺; MALDI-ToF: m/z = 2230.4 [M+H]⁺. Conjugate purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Jupiter Proteo 4 pm 90 A (C12, 250 x 4.6 mm) with linear gradient of 45 % to 85 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 30 min (flow rate: 1 .00 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm 100 A (Biphenyl, 250 x 4.6 mm) with linear gradient of 45 % to 85 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 30 min (flow rate: 1 .55 ml/min, l = 220 nm) showed purities >95 % with retention times of 13.8 min and 13.0 min, respectively.

Reference Example RE8: rK⁸((2S)-Dap(bm9x)₂)1-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with AC₂0 and DIPEA in DCM for 15 min. The Dde protecting group was subsequently cleaved off with 3 % hydrazine in DMF for 10 x 10 min. Fmoc-(2S)-Dap(Fmoc)-OH (3 equiv), HOBt (4 equiv) and DIC (4 equiv) were used for Dap coupling to the free e-amino group of the C-terminal lysine overnight. Subsequent Fmoc deprotection with 20% piperidine in DMF was followed by coupling of the bis-carbaborane bm9x synthon (see Intermediate 5) to the two free amino groups of the previously attached (2S)-Dap branching moiety. For said carbaborane bm9x synthon coupling, 3 equiv of the carbaborane bm9x synthon, 6 equiv DIC and 6 equiv HOBt were dissolved DMF and given to the resin-bonded peptide. After the conjugate had been cleaved from the resin and the side chains had been deprotected with TFA/TIS (90:10, v/v) for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ).

Purification was carried out on a preparative RP-HPLC column (Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm) to give the title compound of reference example RE8. A linear gradient of 45 % to 75 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 30 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. The conjugate was synthesized on a 15 pmol scale and the yield was 3.2 mg (9 % of theory).

Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C81H146N28O14B40S4 (monoisotopic mass: 2303.4 Da; average mass: 2296.9 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1 149.5 [M+2H]²⁺, 766.7 [M+3H]³⁺; 575.3 [M+4H]⁴⁺; MALDI-ToF: m/z = 2304.4 [M+H]⁺. Conjugate purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Jupiter

Proteo 4 pm 90 A (C12, 250 x 4.6 mm) with linear gradient of 40 % to 80 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1.00 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm 100 A (Biphenyl, 250 x 4.6 mm) with linear gradient of 40 % to 80 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) showed purities >95 % with retention times of 21.0 min and 17.4 min, respectively.

Reference Example RE 9: rK⁸ 1-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with Ac₂0 and DIPEA in DCM for 15 min. The Dde protecting group was subsequently cleaved off with 3 % hydrazine in DMF for 10 x 10 min. The resin-bonded peptide was modified with 6-carboxytetramethylrhodamine (Tam) with 2 equiv Tam, 1.9 equiv HATU and 2 equiv DIPEA in DMF, protected from light overnight. After the peptide had been cleaved from the resin and the side chains had been deprotected with TFA/TIS (90:10, v/v) for 3 h, the peptide was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ).

Purification was carried out on a preparative RP-HPLC column (Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm) to give the title compound of reference example RE9. A linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 40 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. The peptide was synthesized on a 15 pmol scale and the yield was 6.4 mg (28 % of theory).

Identity of the Tam modified peptide was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap-MS (HCT, Bruker). The chemical formula is C₇₇H₉₄N₁₈O₁₅ (monoisotopic mass: 1510.7 Da; average mass: 151 1.7 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1512.7 [M+H]⁺, 756.6 [M+2H]²⁺, 504.8 [M+3H]³⁺; MALDI- ToF: m/z = 1511.7 [M+H]⁺. Peptide purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Kinetex 5 pm 100 A (C18, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.0 8% TFA) in H₂0 (0.1 % TFA) over 30 min (flow rate: 1 .55 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm 100 A (Biphenyl, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) showed purities >95 % with retention times of 1 1.4 min and 14.2 min, respectively.

Reference Example RE10: -Dap(m9b,Tam)1-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with Ac₂0 and DIPEA in DCM for 15 min. The Dde protecting group was subsequently cleaved with off 3 % hydrazine in DMF for 10 x 10 min. Fmoc-(2S)-Dap(Mtt)-OH (3 equiv) was coupled to the free e-amino group of the C-terminal lysine in the presence of 4 equiv DIC and 4 equiv HOBt in DMF. Subsequent Fmoc deprotection was carried out with 20 % piperidine in DMF followed by coupling of carbaborane m9b synthon (see Intermediate 3) to the free amino group of the previously introduced (2S)-Dap branching moiety, using 1.5 equiv carbaborane m9b synthon, 3 equiv DIC and 3 equiv HOBt in DMF. Mtt cleavage was then performed with 3 % TFA and 5 %

TIS in DCM. Afterwards, the resin-bonded conjugate was further modified at the remaining free amino group of the previously introduced (2S)-Dap branching moiety with 6-carboxytetramethylrhodamine (Tam) using 2 equiv Tam, 1.9 equiv HATU and 2 equiv DIPEA in DMF, protected from light overnight. After the conjugate had been cleaved from the resin and the side chains had been deprotected with TFA/TIS (90:10, v/v) for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ).

Purification was carried out on a preparative RP-HPLC column (Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm) to give the title compound of reference example RE10. A linear gradient of 20 % to 60 % ACN (0.08 % TFA) in FhO (0.1 % TFA) over 40 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. The conjugate was synthesized on a 15 pmol scale and the yield was 4.2 mg (28 % of theory).

Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C84H112N20O17B10S1 (monoisotopic mass: 1814.9 Da; average mass: 1814.1 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1815.0 [M+H]⁺, 908.1 [M+2H]²⁺, 605.7 [M+3H]³⁺; MALDI-ToF: m/z = 1816.0 [M+H]⁺. Conjugate purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Kinetex 5 pm 100 A (C18, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm 100 A (Biphenyl, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) showed purities >95 % with retention times of 16.4 min and 19.6 min, respectively.

Reference Example RE11 : rK⁸((2S)Dap((2S)-Dap(m9b)₂.Tam))1-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with AC₂0 and DIPEA in DCM for 15 min. The Dde protecting group was subsequently cleaved off with 3 % hydrazine in DMF for 10 x 10 min. Fmoc-(2S)-Dap(Mtt)-OH (3 equiv) was coupled to the free e-amino group of the C-terminal lysine in the presence of 4 equiv DIC and 4 equiv HOBt in DMF. Subsequent Fmoc deprotection was carried out with 20 % piperidine in DMF, followed by coupling of Fmoc-(2S)-Dap(Fmoc)-OH (3 equiv.) to the free amino group of the previously introduced (2S)-Dap branching moiety in the presence of 4 equiv DIC and 4 HOBt in DMF. Fmoc deprotection with 20 % piperidine in DMF was followed by coupling of carbaborane m9b synthon (see Intermediate 3) to the two free amino groups of the newly introduced (2S)-Dap branching moiety using 3 equiv of said carbaborane m9b synthon, 6 equiv DIC and 6 equiv HOBt in DMF. Mtt cleavage was then performed with 3 % TFA and 5 % TIS in DCM. Afterwards, the resin- bonded conjugate was further modified with 6-carboxytetramethylrhodamine (Tam) using 2 equiv Tam, 1.9 equiv HATU and 2 equiv DIPEA in DMF, protected from light overnight. After the conjugate had been cleaved from the resin and the side chains had been deprotected with TFA/TIS (90:10, v/v) for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ).

Purification was carried out on a preparative RP-HPLC column (Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm) to give the title compound of reference example RE11. A linear gradient of 30 % to 70 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 40 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. Compound was synthesized on a 15 pmol scale and the yield was 4.6 mg (14 % of theory).

Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C91H130N22O19B20S2 (monoisotopic mass: 2119.1 Da; average mass: 21 16.5 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 21 17.4 [M+H]⁺, 1059.3 [M+2H]²⁺, 706.6 [M+3H]³⁺; MALDI-ToF: m/z = 2120.2 [M+H]⁺. Conjugate purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Kinetex 5 pm 100 A (C18, 250 x 4.6 mm) with linear gradient of 30 % to 70 % ACN (0.08 % TFA) in H₂O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm 100 A (Biphenyl, 250 x 4.6 mm) with linear gradient of 30 % to 70 % ACN (0.08 % TFA) in H₂O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) showed purities >95 % with retention times of 14.3 min and 17.4 min, respectively.

Reference Example RE12: rK⁸«2S)-Dap«2S)-Dap«2S)-Dap ₂)₂.Tam))1-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with AC₂0 and DIPEA in DCM for 15 min. The Dde protecting group was subsequently cleaved off with 3 % hydrazine in DMF for 10 x 10 min. Fmoc-(2S)-Dap(Mtt)-OH (3 equiv) was coupled to the free e-amino group of the C-terminal lysine in the presence of 4 equiv DIC and 4 equiv HOBt in DMF. After Fmoc deprotection with 20 % piperidine in DMF, Fmoc-(2S)-Dap(Fmoc)-OH (3 equiv.) was coupled to the free amino group of the previously introduced (2S)-Dap branching moiety in the presence of, 4 equiv DIC and 4 equiv HOBt in DMF. Following subsequent Fmoc deprotection, Fmoc-(2S)Dap(Fmoc)-OH (6 equiv) was coupled to the two free amino groups of the newly introduced (2S)-Dap branching moiety in the presence of 8 equiv DIC and 8 equiv HOBt in DMF. After renewed Fmoc deprotection with 20 % piperidine in DMF, carbaborane m9b synthon (see Intermediate 3) was coupled to the in total four free amino groups introduced in the third (2S)-Dap branching and Fmoc cleavage cycle, using 6 equiv of said carbaborane m9b synthon, 12 equiv DIC and 12 equiv HOBt in DMF. Subsequently, Mtt cleavage was then performed with 3 % TFA and 5 % TIS in DCM. Afterwards, the resin-bonded conjugate was further modified with 6-carboxytetramethylrhodamine (Tam) using 2 equiv Tam, 1 .9 equiv HATU and 2 equiv DIPEA in DMF, protected from light overnight. After the fully elaborated conjugate had been cleaved from the resin and the side chains had been deprotected with TFA/TIS (90:10, v/v) for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ). Purification was carried out on a preparative RP-HPLC column (Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm) to give the title compound of reference example RE12. A linear gradient of 40 % to 80 % ACN (0.08 % TFA) in FhO (0.1 % TFA) over 40 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. The conjugate was synthesized on a 15 pmol scale and the yield was 5.6 mg (14 % of theory).

Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C105H166N26O23B40S4 (monoisotopic mass: 2727.5 Da; average mass: 2721.3 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1361.7 [M+2H]²⁺, 908.2 [M+3H]³⁺; MALDI-ToF: m/z = 2728.5 [M+H]⁺. Conjugate purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Jupiter Proteo 4 pm 90 A (C12, 250 x 4.6 mm) with linear gradient of 40 % to 80 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1.00 ml/min, l = 220 nm) and (2) Phenomenex Kinetex 5 pm 100 A (C18, 250 x 4.6 mm) with linear gradient of 40 % to 80 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) showed purities >95 % with retention times of 14.2 min and 15.1 min, respectively.

Reference Example RE13: rK⁸((2S)-Dap((2S)-Dap(bm9x)₂.Tam))1-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with AC₂0 and DIPEA in DCM for 15 min. The Dde protecting group was subsequently cleaved off with 3 % hydrazine in DMF for 10 x 10 min. Fmoc-(2S)-Dap(Mtt)-OH (3 equiv) was coupled to the free e-amino group of the C-terminal lysine in the presence of 4 equiv DIC and 4 equiv HOBt in DMF. Then, Fmoc cleavage was performed with 20 % piperidine in DMF. Subsequently, Fmoc-(2S)-Dap(Fmoc)-OH (3 equiv) was coupled to the free amino group of the previously introduced (2S)-Dap branching moiety in the presence of, DIC (4 equiv) and HOBt (4 equiv) in DMF, followed by cleavage of the Fmoc protecting groups with 20 % piperidine in DMF. Overnight coupling of carbaborane bm9x synthon (see Intermediate 5) to the two free amino groups of the newly introduced (2S)-Dap branching moiety was performed with 3 equiv of said carbaborane bm9x synthon, 6 equiv DIC and 6 equiv HOBt in DMF. Mtt cleavage was performed with 3 % TFA and 5 % TIS in DCM. Afterwards, the resin-bonded conjugate was further modified with 6-carboxytetramethylrhodamine (Tam) using 2 equiv Tam, 1.9 equiv HATU and 2 equiv DIPEA in DMF, protected from light overnight. After the conjugate had been cleaved from the resin and the side chains had been deprotected with TFA/TIS (90:10, v/v) for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ).

Purification was carried out on preparative RP-HPLC column (Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm) to give the title compound of reference example RE13. A linear gradient of 40 % to 80 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 40 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. The conjugate was synthesized on a 15 pmol scale and the yield was 7.6 mg (28 % of theory).

Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C109H172N32O19B40S4 (monoisotopic mass: 2801.6 Da; average mass: 2795.4 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1398.9 [M+2H]²⁺, 932.9 [M+3H]³⁺; 700.0 [M+4H]⁴⁺, 560.2 [M+5H]⁵⁺; MALDI-ToF: m/z = 2802.7 [M+H]⁺. Conjugate purity was analyzed by analytical RP- HPLC: (1 ) Phenomenex Kinetex 5 pm 100 A (C18, 250 x 4.6 mm) with linear gradient of 40 % to 80 % ACN (0.08 % TFA) in H₂O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm 100 A (Biphenyl, 250 x 4.6 mm) with linear gradient of 40 % to 80 % ACN (0.08 % TFA) in H₂O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) showed purities >95 % with retention times of 15.2 min and 16.7 min, respectively.

Reference Example RE14: -Dap(m1J9b,Tam)1-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with Ac₂0 and DIPEA in DCM for 15 min. The Dde protecting group was subsequently cleaved off with 3 % hydrazine in DMF for 10 x 10 min. Fmoc-(2S)-Dap(Mtt)-OH (3 equiv) was coupled was coupled to the free e-amino group of the C-terminal lysine in the presence of, 4 equiv DIC and 4 equiv HOBt in DMF. Subsequent Fmoc deprotection was carried out with 20 % piperidine in DMF, followed by coupling of carbaborane m1J9b synthon (see Intermediate 10) was coupled to the free amino group of the previously introduced (2S)-Dap branching moiety using 1.5 equiv of said carbaborane ml J9b synthon, 3 equiv DIC and 3 equiv HOBt in DMF. Mtt cleavage was then performed with 3 % TFA and 5 % TIS in DCM. Afterwards, the resin-bonded conjugate was further modified with 6-carboxytetramethylrhodamine (Tam) with 2 equiv Tam, 1 .9 equiv HATU and 2 equiv DIPEA in DMF, protected from light overnight. After the conjugate had been cleaved from the resin and the 6-deoxygalactose moiety and the side chains had been deprotected with TFA/TIS (90:10, v/v) for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ). Purification was carried out on a preparative RP-HPLC column (Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm) to give the title compound of reference example RE14. A linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 40 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. The conjugate was synthesized on a 15 pmol scale and the yield was 7.5 mg (25 % of theory). Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C90H122N20O22B10S1 (monoisotopic mass: 1977.0 Da; average mass: 1976.2 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1977.2 [M+H]⁺, 989.2 [M+2H]²⁺, 659.8 [M+3H]³⁺; MALDI-ToF: m/z = 1978.0 [M+H]⁺. Conjugate purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Kinetex

5 pm 100 A (C18, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm 100 A (Biphenyl, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) showed 12.4 min and 15.3 min, respectively. The peak on both columns was split into overlapping peaks. The peaks were not separable, but MALDI-MS analysis showed only one defined signal without side product formation. These findings can be explained by isomerization reactions of the 6- deoxygalactose moiety attached to the carbaborane cluster. The product thus obtained had a chemical purity >95 %.

Reference Example RE15: rK⁸((2S)-Dap((2S)-Dap(m1J9b)₂.Tam))1-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with AC₂0 and DIPEA in DCM for 15 min. The Dde protecting group was subsequently cleaved off with 3 % hydrazine in DMF for 10 x 10 min. Fmoc-(2S)-Dap(Mtt)-OH (3 equiv) was coupled to the free e-amino group of the C-terminal lysine in the presence of 4 equiv DIC and 4 equiv HOBt in DMF. Subsequent Fmoc deprotection was carried out with 20 % piperidine in DMF, followed by coupling of Fmoc-(2S)-Dap(Fmoc)-OH (3 equiv) to the free amino group of the previously introduced (2S)-Dap branching moiety in the presence of 4 equiv DIC and 4 HOBt. Subsequent Fmoc deprotection was carried out with 20 % piperidine in DMF and was followed by coupling of carbaborane m1J9b synthon (see Intermediate 10) to the two free amino groups of the newly introduced (2S)-Dap branching moiety using 3 equiv of said carbaborane m1J9b synthon, 6 equiv DIC and 6 equiv HOBt in DMF. Mtt cleavage was then performed with 3 % TFA and 5 %

TIS in DCM. Afterwards, the resin-bonded conjugate was further modified with 6-carboxytetramethylrhodamine (Tam) using 2 equiv Tam, 1.9 equiv HATU and 2 equiv DIPEA in DMF, protected from light overnight. After the conjugate had been cleaved from the resin and the 6-deoxygalactose moieties and the side chains had been deprotected with TFA/TIS (90:10, v/v) for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ). Purification was carried out on a preparative RP-HPLC column (Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm) to give the title compound of reference example RE15. A linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 40 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. The conjugate was synthesized on a 15 pmol scale and the yield was 3.2 mg (9 % of theory).

Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C103H150N22O29B20S2 (monoisotopic mass: 2443.2 Da; average mass: 2440.7 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1221.5 [M+2H]²⁺, 814.7 [M+3H]³⁺; MALDI-ToF: m/z = 2444.2 [M+H]⁺. Conjugate purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Kinetex 5 pm 100 A (C18, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm 100 A (Biphenyl, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) showed retention times of 13.5 min and 16.4 min, respectively. The peak on both columns was splitted into overlapping peaks. The peaks were not separable, but MALDI-MS analysis showed only one defined signal without side product formation. These findings can be explained by isomerization reactions of the 6- deoxygalactose moieties attached to the carbaborane clusters. The product thus obtained had a chemical purity >95 %.

Reference Example RE16: rK⁸«2S)-Dap«2S)-Dap«2S)-Dap(m1 NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with AC₂0 and DIPEA in DCM for 15 min. The Dde protecting group was subsequently cleaved off with 3 % hydrazine in DMF for 10 x 10 min. Fmoc-(2S)-Dap(Mtt)-OH (3 equiv) was coupled to the free e-amino group of the C-terminal lysine in the presence of 4 equiv DIC and 4 equiv HOBt in DMF. Subsequent Fmoc deprotection was carried out with 20 % piperidine in DMF and was followed by coupling of Fmoc-(2S)-Dap(Fmoc)-OH (3 equiv) to the free amino group of the previously introduced (2S)-Dap branching moiety in the presence of 4 equiv DIC and 4 HOBt in DMF. Following subsequent Fmoc deprotection, Fmoc-(2S)-Dap(Fmoc)-OH (6 equiv) was coupled to the two free amino group of the newly introduced (2S)-Dap branching moiety in the presence of 8 equiv DIC and 8 equiv HOBt in DMF. After renewed Fmoc deprotection with 20 % piperidine in DMF, carbaborane ml J9b synthon (see Intermediate 10) was coupled to the in total four free amino groups introduced in the third (2S)-Dap branching and Fmoc cleavage cycle, using 6 equiv of said carbaborane ml J9b synthon, 12 equiv DIC and 12 equiv HOBt in DMF. Mtt cleavage was then performed with 3 % TFA and 5 % TIS in DCM. Afterwards, the resin-bonded conjugate was further with 6-carboxytetramethylrhodamine (Tam) using 2 equiv Tam, 1.9 equiv HATU and 2 equiv DIPEA in DMF, protected from light overnight. After the fully elaborated conjugate had been cleaved from the resin and the 6-deoxygalactose moieties and the side chains had been deprotected with TFA/TIS (90:10, v/v) for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ).

Purification was carried out on a preparative RP-HPLC column (Phenomenex Biphenyl (5 pm, 100 A, Biphenyl, 250 x 21.2 mm) to give the title compound of reference example RE16. A linear gradient of 20 % to 60 % ACN (0.08 % TFA) in FhO (0.1 % TFA) over 50 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. The conjugate was synthesized on a 15 pmol scale and the yield was 2.7 mg (5 % of theory).

Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C129H206N26O43B40S4 (monoisotopic mass: 3375.7 Da; average mass: 3369.9 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1685.8 [M+2H]²⁺, 1124.4 [M+3H]³⁺, 843.5 [M+4H]⁴⁺; MALDI- ToF: m/z = 3376.9 [M+H]⁺, 1688.9 [M+2H]²⁺. Conjugate purity was analyzed by analytical RP- HPLC: (1 ) Phenomenex Jupiter Proteo 4 pm 90 A (C12, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 30 min (flow rate: 1.00 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm 100 A (Biphenyl, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H₂O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) showed retention times of 14.6 min and 14.9 min, respectively. The peak on both columns was broad due to overlapping peaks. The peaks were not separable, but MALDI-MS analysis showed only one defined signal without side product formation. These findings can be explained by isomerization reactions of the 6-deoxygalactose moieties attached to the carbaborane clusters. The product thus obtained had a chemical purity >95 %.

EXPERIMENTAL SECTION - EXAMPLES

Table 5: Codes and Sequences of Example compounds

Example 1 : GK⁸ J9b)1-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with Ac₂0 and DIPEA in DCM for 15 min. The Dde protecting group was subsequently cleaved off with 3 % hydrazine in DMF for 10 x 10 min. Overnight coupling of carbaborane m1J9b synthon to the free e-amino group of the C-terminal lysine was performed by adding 1.5 equiv of the carbaborane m1J9b synthon (see Intermediate 10), 3 equiv DIC and 3 equiv HOBt to the resin- bonded peptide. After the conjugate had been cleaved from the resin, and the 6-deoxygalactose moiety and the side chains had been deprotected with TFA/TIS (90:10, v/V)for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ).

Purification was carried out on a preparative RP-HPLC column (Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm) to give the title compound of Example 1. A linear gradient of 20 % to 50 % ACN (0.08 % TFA) in FhO (0.1 % TFA) over 30 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. The conjugate was synthesized on a 15 pmol scale and the yield was 8.4 mg (38 % of theory).

Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C₆₂H₉₆N₁₆O₁₇B₁₀S₁ (monoisotopic mass: 1478.8 Da; average mass: 1477.7 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1478.8 [M+H]⁺, 739.9 [M+2H]²⁺; MALDI-ToF: m/z = 1479.8 [M+H]⁺. Conjugate purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Jupiter Proteo 4 pm 90 A (C12, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 30 min (flow rate: 1.00 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm 100 A (Biphenyl, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H₂O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm). The analysis on the Proteo column showed a purity >95 % with a retention time of 17.4 min for a broad product peak. The product peak on the biphenyl column was split into four overlapping peaks (retention times: 11.5 min, 1 1.6 min, 1 1.8 min, and 1 1.9 min). The peaks were not separable, but MALDI-MS analysis showed only one defined signal without side product formation. These findings can be explained by isomerization reactions of the 6-deoxygalactose moiety attached to the carbaborane cluster. The product thus obtained had a chemical purity >95 %.

Example 2: rK⁸«2S)-Dap(m1 J9b)₂)1-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with AC₂0 and DIPEA in DCM for 15 min. The Dde protecting group was subsequently cleaved off with 3 % hydrazine in DMF for 10 x 10 min. Fmoc-(2S)-Dap(Fmoc)-OH was coupled to the free e-amino group of the C-terminal lysine by adding 3 equiv Fmoc-(2S)-Dap(Fmoc)-OH, 4 equiv DIC and 4 equiv HOBt in DMF to the resin-bonded peptide. Subsequent Fmoc deprotection with 20 % piperidine in DMF was followed by coupling of the carbaborane m1J9b synthon (see

Intermediate 10) to the two free amino groups of the previously attached (2S)-Dap branching moiety. For said coupling, 3 equiv of the carbaborane ml J9b synthon, 6 equiv DIC and 6 equiv HOBt were dissolved in DMF and were added to the resin-bonded peptide. After the conjugate had been cleaved from the resin and the 6-deoxygalactose moieties and the side chains had been deprotected with TFA/TIS (90:10, v/v) for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ).

Purification was carried out on a preparative RP-HPLC column (Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm) to give the title compound of Example 2. A linear gradient of 25 % to 55 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. The conjugate was synthesized on a 15 pmol scale and the yield was 8.5 mg (29 % of theory). Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C75H124N18O24B20S2 (monoisotopic mass: 1945.0 Da; average mass: 1942.2 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1943.2 [M+H]⁺, 972.2 [M+2H]²⁺; MALDI-ToF: m/z = 1946.0 [M+H]⁺. Conjugate purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Jupiter Proteo 4 pm 90 A (C12, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 30 min (flow rate: 1.00 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm 100 A (Biphenyl, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm). The analysis on the Proteo column showed a purity >95 % with a retention time of 18.6 min for a very broad product peak. The peak on the biphenyl column was split into four overlapping peaks (retention times: 13.2 min, 13.4 min, 13.6 min, and 13.8 min). The peaks were not separable, but MALDI-MS analysis showed only one defined signal without side product formation. These findings can be explained by isomerization reactions of the 6-deoxygalactose moieties attached to the carbaborane clusters. The product thus obtained had a chemical purity >95 %.

Example 3: rK⁸«2S)-Dap«2S)-Dap(m1J9b)₂)₂)1-NAPamide

After automated synthesis of the side chain protected, resin-bonded intermediate peptide L-Nle - L-Asp(tBu) - L-His(Trt) - D-Phe - L-Arg(Pbf) - L-Trp(Boc) - Gly - L-Lys(Dde), corresponding to the sequence L^NDHfRWGK, the N-terminus of said resin-bonded peptide was acetylated with AC₂0 and DIPEA in DCM for 15 min. The Dde protecting group was subsequently cleaved off with 3 % hydrazine in DMF for 10 x 10 min. The coupling of (2S)-2,3-diaminopropionic acid branching moiety to the free e-amino group of the C-terminal lysine was performed by using Fmoc-(2S)-Dap(Fmoc)-OH (3 equiv), DIC (4 equiv) and HOBt (4 equiv) in DMF. Subsequent Fmoc deprotection was done by using 20 % piperidine in DMF. Then, 6 equiv Fmoc-(2S)- Dap(Fmoc)-OH, 8 equiv DIC and 8 equiv HOBt in DMF were coupled to the two free amino groups of the previously attached (2S)-Dap branching moiety. Fmoc deprotection was carried out with 20 % piperidine in DMF, followed by coupling of carbaborane m1J9b synthon (see Intermediate 10) to the in total four free amino groups of the previously attached (2S)-Dap branching moieties, which was performed with 6 equiv of carbaborane m1J9b synthon, 12 equiv DIC and 12 equiv HOBt in DMF. After the conjugate had been cleaved from the resin and the 6- deoxygalactose moieties and the side chains had been deprotected with TFA/TIS (90:10, v/v) for 3 h, the conjugate was precipitated and washed with ice-cold diethyl ether/hexane (4:1 ). Purification was carried out on preparative RP-HPLC column (Phenomenex Aeris 5 pm PEPTIDE XB C18, 250 x 21.2 mm) to give the title compound of Example 3. A linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H₂0 (0.1 % TFA) over 40 min was applied. The flow rate was 15 mL/min, UV detection was measured at l = 220 nm. The conjugate was synthesized on a 7.5 pmol scale and the yield was 1.5 mg (7 % of theory). Identity of the conjugate was confirmed by MALDI-ToF-MS (Ultraflexlll, Bruker) and ESI-lontrap- MS (HCT, Bruker). The chemical formula is C101H180N22O38B40S4 (monoisotopic mass: 2877.5 Da; average mass: 2871.3 Da). The observed masses were in correspondence to the calculated mass. ESI lontrap: m/z = 1436.9 [M+2H]²⁺, 958.2 [M+3H]³⁺; MALDI-ToF: m/z = 2878.6 [M+H]⁺. Conjugate purity was analyzed by analytical RP-HPLC: (1 ) Phenomenex Jupiter Proteo 4 pm 90 A (C12, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1.00 ml/min, l = 220 nm) and (2) Phenomenex Biphenyl 5 pm 100 A (Biphenyl, 250 x 4.6 mm) with linear gradient of 20 % to 60 % ACN (0.08 % TFA) in H2O (0.1 % TFA) over 30 min (flow rate: 1.55 ml/min, l = 220 nm) showed purities >95 % with retention times of 16.0 min and 13.4 min, respectively. Both analytical RP-HPLC runs showed a broad product peak, showing one signal in the MS analytics. The product thus obtained had a chemical purity >95 %.

Tables 6a, 6b and 6c: Peptide / Conjugate Analysis

Analysis of the synthesized peptides/conjugates was performed by RP-HPLC with linear gradients of eluent A (H₂0 containing 0.1 % TFA) and eluent B (ACN containing 0.08 % TFA). Peptide/conjugate analysis was carried out by measuring the absorbance at 220 nm and the Tam fluorescence at 572 nm on two different RP-HPLC columns for verification, which are shown in Table 6a.

Table 6a: RP-HPLC columns used for peptide/conjugate analysis. The shown columns are described by their characteristics provided from the manufacturer, the flow rate used for peptide/conjugate elution and a system code, which will be used further on for abbreviation.

The gradients used for peptide/conjugate elution were adapted to each peptide/conjugate individually depending on the hydrophobicity of the compound (gradients shown in Table 6b)

Table 6b:Gradients of eluent B (ACN containing 0.08 % TFA) in eluent A (H₂0 containing 0.1 % TFA) used for peptide analysis. The gradient codes are used for further abbreviation of the gradients of eluent B in eluent A, which were used for peptide elution for RP-HPLC analysis.

Preparative RP-HPLC with linear gradients of eluent A (H₂0 containing 0.1 % TFA) in eluent B (ACN containing 0.08 % TFA) was applied for peptide purification. Peptide identification was achieved by investigating the monoisotopic mass by MALDI-ToF MS and average mass by ESI- iontrap MS, if not indicated otherwise.

Table 6c: Parameters of analysis by RP-HPLC of the synthesized compounds on two different columns. For each compound the exploited columns and gradients are given by their abbreviation defined in the previous tables. Additionally, the retention time and ACN concentration needed for peptide elution from the individual column is given and used for peptide characterization (^*: flow rate reduced to 0.6 ml/min).

EXPERIMENTAL SECTION - BIOLOGICAL ASSAYS

Examples and reference examples were tested in selected biological assays one or more times. When tested more than once, data are reported as either average values or as median values, wherein

· the average value, also referred to as the arithmetic mean value, represents the sum of the values obtained divided by the number of times tested, and

• the median value represents the middle number of the group of values when ranked in ascending or descending order. If the number of values in the data set is odd, the median is the middle value. If the number of values in the data set is even, the median is the arithmetic mean of the two middle values.

Examples and reference examples were synthesized one or more times. When synthesized more than once, data from biological assays represent average values or median values calculated utilizing data sets obtained from testing of one or more synthetic batch.

Molecular Biology

The MCiR cDNA with an N-terminal HA tag and a C-terminal FLAG-tag was obtained in a pcDps vector (HA-MCiR-FLAG_pcDps). The cDNA was amplified and restriction sites were introduced using 5’-AAAG AT ATC CT C AAG CTTG C C AC CAT GTACCCCTACG-3’ and 5’- TTTT GT ACAAACCTGCT CT CACTT AT CGT CAT CGTCCT-3’ . Digestion of the PCR product HA-

MCiR-FLAG and the pVitro2 plasmid was performed with EcoRV and Bsp1407 (Thermo Scientific, Waltham, MA, USA) for 3 h at 37 °C. The subsequent ligation reaction of digested backbone DNA and digested PCR product was achieved using T4-DNA ligase (Thermo Scientific) for 1 h at RT. Sequencing confirmed correct ligation product. The plasmid was amplified using E. coli DH5a. HA-MCiR-FLAG_pV2, was linearized with Xhol (Thermo Scientific) and HEK293 cells were stably transfected with the vector using Lipofectamine™ 2000 (Invitrogen, Carlsbad, CA, USA). Cells were then selected with hygromycin (Invitrogen).

Cell Culture and cAMP Assay

HEK293_HA_MCiR_FLAG, expressing the MCiR due to stable transfection, were transiently transfected with the plasmid pGL4.29[luc2P/CRE/Hygro] (Promega). Transient transfection was carried out in 75 cm² cell culture flasks with cell monolayers (confluency of -80 %). 12 pg plasmid DNA and 45 pi MetafectenePro were separately added to 900 pi DMEM/Ham’s F12 before unification and incubation at RT for 20 min. The cell monolayer was incubated with 6 ml DMEM/Ham’s F12 with additives (15 % FCS and 0.1 mg/ml hygromycin) at 37 °C for 20 min. Then, the plasmid solution was added and cells were incubated with the plasmid for 3 h at 37° C before the medium replacement with 13 ml plasmid-free medium. Cells were grown overnight before seeding. Cell seeding was carried out in white 96-well polystyrene cell culture microplates, coated with poly-D-lysine. Transfected HEK293_HA_MCiR_FLAG cells were detached with 1 ml trypsin/EDTA. The number of cells/ml medium was counted after adding 9 ml of DMEM/Ham’s F12 with additives in a Neubauer chamber. The cell suspension was diluted to 100,000 cells/150 mI, which were seeded. Afterwards, the cells were incubated overnight at 37° C. The assay was performed under unsterile conditions. First, the cells were staved with 50 mI of DMEM/Ham’s F12 for 1 h at 37° C. Afterwards the cells were stimulated with the peptides or conjugates dissolved in DMEM/Ham’s F12. 50 mI of the peptide dilution were used for cell stimulation. Medium without peptide was used as a negative control and 1 mM forskolin was used as a positive control. The cells were stimulated for 3 h at 37° C before removing the peptide or conjugate solution and washing with 50 mI of DMEM/Ham’s F12. 30 mI of medium were added and the cells were incubated for 10 min at RT before adding 30 mI of ONE-Glo (Promega). The microplate was incubated for 5 min in the plate reader before the emitted luminescence was measured. The measured luminescence was processed by non-linear regression (GraphPad Prism), creating concentration-effect-curves. The curves were normalized to 100 % (positive control) and 0 % (negative control). From these normalized curves, the ECso and E_max values were determined. The ECso value represents the peptide/conjugate concentration where 50% of its maximal effect is observed and the E_max value is describes the maximum effect caused by peptide/conjugate binding to the receptor in comparison to the unstimulated negative control. Internalization Studies

The cellular peptide/conjugate uptake was tested in HEK293_HA_MCiR_FLAG cells and HEK293_hYiR_YFP. Ibidi 15p-slides were coated with poly-D-lysine before cell seeding. Cells were washed with DPBS prior to detachment with 1 ml trypsin/EDTA. A Neubauer chamber was used to count the amount of cells/ml medium after addition of 9 ml DMEM/Ham’s F12 with additives (15 % FCS and 0.1 mg/ml hygromycin). The cell suspension was diluted to 150,000 cells/300 pi, which were seeded. Incubation was carried out overnight at 37 °C prior to microscopy studies. Then, the cells were starved with 150 mI OptiMEM for 30 min and after 15 min, 1 mI of Hoechst 33342 was added. The medium was replaced by 200 mI of OptiMEM and the to status was documented. The OptiMEM was then replaced by 200 mI of 10 ⁷ M Tam-labelled peptide/conjugate in OptiMEM. After the stimulation, the cells were washed once with 200 mI of acidic wash buffer (0.05 M glycine, 0.1 M NaCI, pH 3.2) for 30 s and twice with 200 mI HBSS. 200 mI OptiMEM were added for the microscopy. Fluorophore excitation was analyzed by using different filters, depending on the emission wavelength of the fluorophore and the time of exposure was adjusted to each fluorophore individually. All images were processed identically with the AxioVision software (Carl Zeiss AG, Oberkochen, Germany).

Table 7: Filter sets (Zeiss) used for fluorophore detection. Fluorophore excitation and emission wavelength used for fluorescence microscopy are also given.

Fluorophore Used for labeling Filter Excitation [nm] Emission [nm]

Hoechst33342 cell nucleus 02 352 455

Tam peptide 31 549 577

YFP hYi receptor 46 514 526

Tam: 6-carboxytetramethylrhodamine; Hoechst33342: 2’-(4-Ethoxyphenyl)-6-(4-methyl-1- piperazinyl)-1 /-/,3’/-/-2,5’-bibenzimidazole; hYi receptor: human Yi receptor; YFP: yellow fluorescent protein Results

Activity Studies from cAMP Assay

The cAMP assay was used to determine the potency of the synthesized NAPamide analogous peptides/conjugates to activate intracellular signal cascades through the MCiR. For this assay, HEK293_HA_MCiR_FLAG cells were exploited after transient transfection with a CRE-controlled luciferase gene. The transfected cells were seeded and stimulated with different peptide/conjugate concentrations, resulting in measurable luminescence after substrate addition. The sigmoidal concentration-response-curves were normalized to unstimulated cells (negative control; 0 % signal) and forskolin stimulated cells (positive control; 100 % signal). The Tam-labelled analogs were tested in the cAMP assay prior to microscopic studies. It could be shown in the cAMP signal transduction assays that almost all of the synthesized carbaborane conjugated peptides are still able to activate the MCi receptor (see Table 8).

Table 8: ECso values of Reference Examples RE1-RE16, and of Examples 1 -3, determined by cAMP-assays. The EC₅o, pECso, E_max and their SEM are shown (n > 2).

The conjugation of carbaborane moieties causes a shift to higher EC₅₀ values in all cases as compared to the boron-free peptides RE1 , RE2 and RE9. However, the extent of said shift strongly depends on the kind of carbaborane moiety attached to the peptide backbone. The incorporation of bis-cluster carbaborane bm9x moieties (RE8, RE13) decreased the receptor activation potency even further when compared to NAPamide conjugates featuring the monomeric carbaborane m9b moieties (e.g. RE7).

Compared to said NAPamide conjugates featuring the monomeric carbaborane m9b moieties (e.g. RE5, RE6 and RE7), their analogues featuring saccharide functionalised carbaborane moieties (Examples 1 , 2 and 3) show higher potencies at the melanocortin 1 receptor while having an equal amount of incorporated boron atoms. Thus, highly active analogues with EC₅₀ values in the low nanomolar range, constituting compounds of the present invention, could be identified. Due to the higher potencies mediated via saccharide functionalised carbaboranes, compounds containing such boron clusters display superior characteristics for potential usage as BNCT agents.

Receptor-Mediated Internalization in HEK293_HA_MCiR_FLAG Cells

After verifying the potency of the peptides/conjugates at the MCiR via signal transduction assay, their internalization behavior was analyzed. Microscopic studies (Table 9) were carried out with Tam-labelled peptides and HEK293 cells, expressing the MCiR due to stable transfection. All fluorescent peptide analogs were tested, blue-colored shapes show stained nuclei and red- colored structures represent Tam-labelled peptides. At t = 0 min, no red fluorescence was observable for all peptides. The cell nuclei showed an oval shaped morphology.

Table 9: Analysis of internalization studies of NAPamide-carbaborane-conjugates.

HEK293 cells expressing the MCiR due to stable transfection or the eYFP-tagged hYiR due to stable transfection were used for the internalization studies. Internalization was induced by stimulating the cells with 10 ⁷ M Tam-labelled peptide (red) and was documented via fluorescence microscopy after nuclei staining (blue); scale bar: 20 pm; n = 2

+: internalization was comparable to RE9 [K⁸(Tam)]-NAPamide

+ +: internalization was increased in comparison to RE9 [K⁸(Tam)]-NAPamide

-: internalization was decreased in comparison to RE9 [K⁸(Tam)]-NAPamide

- -: no internalization was observed

"Internalization was not investigated by fluorescence microscopy due to the peptides not containing a fluorescence marker (e.g. Tam fluorophore)

After stimulation with RE2 (N-terminally modified NAPamide) and RE9 (C-terminal side chain modified NAPamide) for 60 min, intensive red fluorescence was detectable in the cytosol for both compounds, indicating high cellular uptake of the peptides independent from the modification site. Decreased uptake was detected for RE4 after cellular stimulation. The internalization of RE10 was similar to RE9. RE11 already internalized mostly after 15 min stimulation. The overall observed Tarn-fluorescence was lower compared to other NAPamide analogs. Further, decreased Tarn-fluorescence was detected for the four carbaborane- containing RE12 at the 60 min time point of stimulation. In contrast to the previous compounds, no internalization was observed for RE13, containing two of the bis-cluster carbaborane bm9x moieties. In addition to the low internalization, extracellular peptide precipitation was observed for the highly hydrophobic compounds RE12 and RE13. The sugar-carbaborane containing compounds RE14 and RE15, constituting the Tam-labelled analogues to Examples 1 and 2, internalize similarly to RE9. In contrast to compound RE12 containing four carbaborane m9b moieties, RE16, constituting the Tam-labelled analogue to Example 3, and featuring four carbaborane m1J9b moieties, still internalizes via the MCi receptor. Notably, no extracellular precipitation was observable for all NAPamide analogs containing saccharide-modified carbaborane moieties. Thus, the introduction of the saccharide moiety increases the hydrophilicity of the compound and improves its potential as boron carrierfor possible application in BNCT. Internalization in HEK293_hYiR_YFP Cells

To verify the specific internalization of the most promising compounds via the MCi receptor, HEK293_hYiR_YFP cells were used. These cells express the human Yi receptor (hYiR) with a C-terminally yellow fluorescent protein (YFP). The NAPamide analogs are not expected to bind to this receptor. Thus, no internalization should be observed. The selective hYiR agonist Tam-[F⁷,P³⁴]-Neuropeptide Y (Tam-[F⁷,P³⁴]-NPY) was used as a positive control in these experiments (Table 9). Cell incubation with each peptide was carried out for 60 min. Without stimulation, the receptor was located at the cell membrane, but co-internalized after stimulation with Tam-NPY for 60 min. No internalization of the hYi receptor was observable for all tested Tam-labelled analogs of NAPamide-carbaborane-conjugates. Thus, all synthesized NAPamide analogs specifically internalize via the MC-iR-mediated process.

Claims

1. A compound of general formula (I):

in which :

R¹ represents a group R²-C(=0)-, in which R² represents a group selected from Ci-C₆-alkyl, phenyl-Ci-C3-alkyl-, and phenyl, in which the phenyl group and the phenyl present in phenyl-Ci-C3-alkyl- are optionally substituted, one, two or three times, identically or differently, with a group selected from a halogen atom, Ci-C3-alkyl, and Ci-C3-alkoxy,

X¹ represents an amino acid selected from L-norleucine, D-norleucine, norleucine as isomeric mixture, L-methionine, D-methionine, and methionine as isomeric mixture,

L-His represents L-histidine,

L-Arg represents L-arginine,

r represents an integer selected from 0, 1 , 2, 3 and 4, CbD represents a group selected from

Cb-$,

which

$ represents the point of attachment to the rest of the molecule,

Cb represents a group

Sac

Sac represents a group selected from

and

“o” represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group

Cb,

or an isomer resulting from a mutarotation reaction, a tautomer, an N-oxide, a hydrate, a solvate, or a salt thereof, or a mixture of same.

2. A compound of general formula (I), according to claim 1

in which :

R¹ represents a group R²-C(=0)-, in which R² represents a group selected from Ci-C3-alkyl and phenyl, in which the phenyl group is optionally substituted, one, two or three times, identically or differently, with a group selected from a fluorine atom, a chlorine atom, methyl and methoxy,

X¹ represents an amino acid selected from L-norleucine and L-methionine,

L-His represents L-histidine,

L-Arg represents L-arginine,

r represents an integer selected from 1 , 2 and 3,

CbD represents a group selected from

Cb-$,

which q represents an integer 1 ,

Sac represents a group selected from

and

“o” represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group

Cb,

or an isomer resulting from a mutarotation reaction, a tautomer, an N-oxide, a hydrate, a solvate, or a salt thereof, or a mixture of same. A compound of general formula (I), according to claim 1

X¹ represents an amino acid selected from L-norleucine and L-methionine,

L-His represents L-histidine,

L-Arg represents L-arginine,

r represents an integer selected from 2 and 3,

CbD represents a group selected from

Cb-$, , in which q represents an integer 1 ,

$ represents the point of attachment to the rest of the molecule,

Cb represents a group

Sac represents a group selected from

represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group Cb,

4. A compound of general formula (I), according to claim 1 or 2,

in which :

X¹ represents L-norleucine,

X² represents L-aspartic acid,

L-His represents L-histidine,

X³ represents D-phenylalanine,

L-Arg represents L-arginine,

X⁴ represents L-tryptophan,

X⁵ represents glycine,

r represents an integer selected from 2 and 3,

CbD represents a group selected from

Cb-$,

which

q represents an integer 1 ,

$ represents the point of attachment to the rest of the molecule,

Cb represents a group

Sac represents a group selected from

and

“•” represents a boron atom which is bonded to a hydrogen atom in addition to the bonds shown within the group Cb, and

“o” represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group

Cb,

5. A compound of general formula (I), according to any one of claim 1 to 4,

in which :

R¹ represents a group CH₃-C(=0)-,

X¹ represents L-norleucine,

X² represents L-aspartic acid,

L-His represents L-histidine,

X³ represents D-phenylalanine, L-Arg represents L-arginine,

X⁴ represents L-tryptophan,

X⁵ represents glycine,

r represents an integer 3,

CbD represents a group selected from

Cb-$,

which

q represents an integer 1 ,

$ represents the point of attachment to the rest of the molecule,

Cb represents a group

Sac represents a group

represents a boron atom which is bonded to -S-CH₂-C(=0)- in the group Cb,

or an isomer resulting from a mutarotation reaction, a tautomer, a hydrate, a solvate, or a salt thereof, or a mixture of same.

6. The compound according to any one of claim 1 to 5, which is selected from the group consisting of:

- [K⁸(m1J9b)]-NAPamide

[K⁸((2S)-Dap((2S)-Dap(m1 J9b)₂)₂)]-NAPamide

7. A compound of general formula (I), according to any one of claims 1 to 6, for use in the treatment or prophylaxis of cancer.

8. A pharmaceutical composition comprising a compound of general formula (I), according to any one of claims 1 to 6, and one or more pharmaceutically acceptable excipients.

9. A pharmaceutical combination comprising:

• one or more first active ingredients, in particular compounds of general formula (I), according to any one of claims 1 to 6, and

• one or more further active ingredients, in particular agents for the treatment and/or prophylaxis of cancer.

10. Use of a compound of general formula (I), according to any one of claims 1 to 6, for the treatment or prophylaxis of cancer.

1 1 . Use of a compound of general formula (I), according to any one of claims 1 to 6, for the preparation of a medicament for the treatment or prophylaxis of cancer.

12. Use according to claim 7, 10 or 11 , wherein the cancer is skin cancer.