Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07K—PEPTIDES
  • C07K5/00—Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof
  • C07K5/02—Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof containing at least one abnormal peptide link
  • C07K5/0207—Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof containing at least one abnormal peptide link containing the structure -NH-(X)4-C(=0), e.g. 'isosters', replacing two amino acids
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07K—PEPTIDES
  • C07K5/00—Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof
  • C07K5/04—Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof containing only normal peptide links
  • C07K5/12—Cyclic peptides with only normal peptide bonds in the ring
  • C07K5/126—Tetrapeptides
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/50—Improvements relating to the production of bulk chemicals
  • Y02P20/55—Design of synthesis routes, e.g. reducing the use of auxiliary or protecting groups

Definitions

• the present invention relates to a process for the preparation of cyclic tetrapeptide derivatives.
• Cyclic tetrapeptides are a well known class of compounds. There are nineteen naturally occurring cyclic tetrapeptides currently recognised, such as trapoxin A and B, chlamydocin, HC toxin I, II and III, bottromycin, apicidin, apicidin A, dihydrotentoxin, tentoxin and fenestin. However, viable synthetic routes to cyclic tetrapeptides and cyclic tetrapeptide derivatives have proved difficult to develop.
• the central synthetic challenge which must be addressed in preparing cyclic tetrapeptides and synthetic derivatives thereof is the construction of the macrocyclic core. This is usually effected by ring closure of the corresponding linear tetrapeptide or tetrapeptide derivative. Such ring closure reactions are characterised by low yields, often due to the formation of the corresponding cyclooctapeptides via an intermolecular, head to tail dimerization process, even under high dilution conditions. Moreover, the success of the cyclisation process is very much dependent on the sequence and configuration of the amino acids present in the linear precursor.
• the present invention provides a process for the preparation of a compound of formula (II),
• each of B ⁇ B 2 , B 3 and B 4 independently represent the skeleton of an ⁇ -amino acid
• D 1 ⁇ D 2 and D 3 each independently represent carbonyl or methylene, with the proviso that only one of the groups selected from D ⁇ D 2 , and D 3 can be methylene
• T 1 t T 2 and T 3 which are optionally present, each independently represent hydrogen or an amino acid substituent or an activating group, an amine protecting group or a linker group, which process comprises cyclising a compound of formula (III)
• P is hydrogen or a carboxyl protecting group or a linker group.
• the present invention provides a general route to cyclic tetrapeptide reduced isosteres. This route may enable combinatorial chemistry techniques, which are unsuitable for the synthesis of fully oxidised tetrapeptides, to be applied to the synthesis of the corresponding partially reduced cyclic tetrapeptides.
• D 1 and one of D 2 or D 3 represent carbonyl and the other one of D 2 or D 3 represents methylene.
• D 3 is methylene and D ⁇ and D 2 are carbonyl.
• D 2 is methylene and D. and D 3 are carbonyl.
• B 1 ( B 2 , B 3 and B 4 each independently represent the skeleton of any proteinogenic or non-proteinogenic ⁇ -amino acid.
• B B 2 , B 3 and B 4 each independently represent the skeleton of any proteinogenic or non-proteinogenic ⁇ -amino acid.
• B B 2 , B 3 and B 4 each independently represent the skeleton of any proteinogenic or non-proteinogenic ⁇ -amino acid.
• B 4 each independently represent the skeleton of any proteinogenic ⁇ -amino acid.
• a preferred class of compounds of formula (II) is that wherein at least one of B 1 t B 2 , B 3 and B 4 represents the skeleton of any non-proteinogenic ⁇ -amino acid.
• Compounds of formula (II) wherein one of B., B 2 , B 3 and B 4 represents the skeleton of any non-proteinogenic ⁇ -amino acid are particluarly preferred.
• B 1 ? B 2) B 3 and B 4 may each independently be of either L or D configuration.
• a convenient class of compounds of formula (II) are those wherein one of B.,, B 2 , B 3 and B 4 is in the D configuration.
• a preferred class of compounds of formula (I) are those wherein B 1 t B 2 , B 3 and B 4 are all of the L configuration.
• amino acid substituent as used herein in the definition of T 1 t T 2 and T 3 is intended to cover any organic substituent which is bound to the ⁇ nitrogen atom of an amino acid used in the synthesis of a compound of formula (II) or (III), for example where the amino acid ⁇ /-methyl alanine is used in the synthesis of a compound of formula (II) or (III) the amino acid substituent is methyl.
• ⁇ -amino acid as used herein is intended to encompass both proteinogenic and non-proteinogenic ⁇ -amino acids.
• Suitable ⁇ -amino acids for use according to the invention include alanine, 2-aminobutyric acid, ⁇ - aminoisobutyric acid, (S)-2-amino-8-oxo-decanoic acid, ⁇ -aminosuberic acid, arginine, asparagine, aspartic acid, 4-chlorophenylalanine, citrulline, ⁇ - cyclohexylalanine, cysteine, cystine, 3,4-dehydroproline, 3,5-diiodotyrosine, 2- fluorophenylalanine, 3-fiuorophenylalanine, 4-fluorophenylalanine, glutamic acid, glutamine, glycine, histidine, homocitrulline, homoserine, frat7s-4-hydroxyproline, ⁇ -hydroxyvaline, isole
• B ⁇ B 2 , B 3 and B 4 each independently represent the skeleton of any ⁇ - amino acid having a molecular weight of less than 400 amu.
• B.,, B 2 , B 3 and B 4 each independently represent the skeleton of any ⁇ -amino acid having a molecular weight of less than 350 amu.
• Another class of compounds of formula (II) is that wherein, B.,, B 2 , B 3 and B 4 each independently represent the skeleton of any ⁇ -amino acid having a molecular weight of less than 250 amu.
• Reference to molecular weight means the molecular weight of the ⁇ -amino acid skeleton excluding protecting groups, activating groups, linker groups, solid resins and the like which may be bound to the ⁇ -amino acid.
• the T group attached to the nitrogen atom adjacent to the D group that is methylene is an activating group and/or an amine protecting group and/or a linker group and the remaining T groups are hydrogen or amino acid substituents.
• D 3 is methylene
• T 3 is an activating group, amine protecting group or linker group and T
• T 2 are hydrogen or amino acid substituents.
• D 2 is methylene
• T, and T 3 are hydrogen or amino acid substituents and T 2 is an activating group, amine protecting group or linker group.
• ⁇ -amino acid skeleton is used herein to define the part of an ⁇ -amino acid excluding the amine group or residue thereof and the carboxyl group or residue thereof.
• the skeleton of the ⁇ -amino acid alanine is ethyl
• the skeleton of the ⁇ -amino acid ⁇ -aminoisobutyric acid is 2-propyl
• the skeleton of the ⁇ -amino acid isoleucine is 2-methylbutyl
• the skeleton of the ⁇ -amino acid tryptophan is 3-ethylindole
• the skeleton of the ⁇ -amino acid 2-amino-8-oxo- decanoic acid is 7-oxo-nonanyl.
• the ⁇ -amino acid skeleton may, together with the ⁇ nitrogen atom of the amino acid to which it is bound, form a heterocyclic ring, such as in, for example, proline and pipecolic acid.
• activating group is used herein to describe a group capable of activating the nitrogen atom to which it is attached such that the nitrogen atom will undergo a coupling reaction with a suitable substrate.
• the coupling reaction will be performed under Mitsunobu conditions, see O. Mitsunobu, Synthesis, 1981 , 1 , 1.
• Convenient activating groups include aromatic sulfonyl groups, alkyl sulfonyl groups and carbamate groups.
• the activating group is selected from 2-nitrobenzenesulfonyl, 4-nitrobenzenesulfonyl and 2,4-dinitrobenzenesulfonyl. Most preferably, the activating group is 2- nitrobenzenesulfonyl.
• linker group is used herein to mean the organic group or part of a group which binds the reacting substrate or reaction product, for example the compound of formula (II) or formula (III), to the polymeric support of a suitable resin.
• suitable resins for connection to the C-terminus of the linear tetrapeptide derivative include 4-hydroxymethyl-3-methoxyphenoxybutyryl MBHA (HMPB- MBHA) resin, and 4-(2 ' 4 ' -dimethoxyphenyl-hydroxymethyl)-phenoxy (Rink Acid) resin and modified Wang resins such as the chlorotrityl resin.
• HMPB- MBHA 4-hydroxymethyl-3-methoxyphenoxybutyryl MBHA
• Rink Acid 4-(2 ' 4 ' -dimethoxyphenyl-hydroxymethyl)-phenoxy (Rink Acid) resin
• modified Wang resins such as the chlorotrityl resin.
• Such resins are commercially available and may be used in a conventional manner.
• Suitable resins for connection to one of the ⁇ nitogen atoms of, for example, the compound of formula (II) or formula (III), include 4-(bromomethyl)phenoxyethyl polystyrene and 4-(bromomethyl)phenoxymethyl polystyrene.
• Such resins are commercially available and may be used in a conventional manner.
• any one of T, to T 3 may be a group which is both an amine protecting group and a linker group, for example by using an amine protecting group bound to a resin, such reagents are commercially available and may be used in a conventional manner.
• any one of T, to T 3 may be a group which is an activating group and an amine protecting group and a linker group.
• an activating group and an amine protecting group and a linker group For example see: P. J. Murray, C. Kay, L. Sandow, A. B. Holmes., Tetrahedron Lett., 1997, 38, 6941 ; wherein aromatic sulfonyl groups, previously disclosed herein as suitable activating groups, are described bound to solid supports.
• Preferably only one of T, to T 3 is an amine protecting group and/or activating group and/or linker group and the remaining T groups are hydrogen or amino acid substituents.
• Compounds of formula (III) may be cleaved from the solid resin prior to cyclisation.
• the compound of formula (II) may be cleaved from the solid resin following cyclisation, for example when one of T, to T 3 is an activating group such as a 2-nitrobenzenesulfonyi bound to a solid support as described above, cleavage may occur at the sulphonamide moiety as described by T. Fukuyama, K.-C. Jow, M. Cheung, Tetrahedron Lett, 1995, 36, 6373.
• the compound of formual (II) may be cleaved from the solid resin concomitant with cyclisation.
• the cleavage site may be located at a position on the linker group such that on cleavage the activating group remains attached to the compound of formula (II).
• T 1 f T 2 and T 3 each independently represent hydrogen or an amino acid substituent or an activating group or an amine protecting group.
• P is hydrogen or a carboxyl protecting group.
• Typical amine and carboxyl protecting groups are well known to those skilled in the art and may be used in a conventional manner. See, for example: "Protective Groups in Organic Synthesis” by T. W. Greene and P. G. M. Wuts (John Wiley & Sons, 1991) or "Protecting Groups” by P. J. Kocienski (Georg Thieme Verlag, 1994).
• suitable amine protecting groups include acyl type protecting groups e.g. formyl, trifluoroacetyl, acetyl, urethane type protecting groups e.g.
• benzyloxycarbonyl (Cbz), substituted benzyloxycarbonyl, 9-fluorenylmethoxycarbonyl (Fmoc), f-butyloxycarbonyl (Boc), isopropyloxycarbonyl, cyclohexyloxycarbonyl and alkyl type protecting groups e.g. benzyl, trityl, chlorotrityl.
• Preferred ⁇ -amine protecting groups are those that may be cleaved under mild acidic conditions, such as Boc, chlorotrityl, and benzophenone imine.
• carboxyl protecting groups include esters such as fetf-butyl ester.
• the cyclisation process may be effected under conventional peptide coupling conditions which are well known to those skilled in the art.
• Solid Phase Peptide Synthesis J. M. Stewart, J. D. Young, (2nd ed., Rockford, Pierce Chemical Co., 1984).
• the cyclisation process may be carried out in the presence of any suitable organic solvent.
• a medium comprising one or more aprotic solvents may be employed.
• Suitable solvents include chlorinated solvents such as dichloromethane or chloroform, amides for example DMF, ⁇ /-methylpyrrolidinone or dimethylacetamide and mixtures thereof, with dimethylformamide / dichloromethane mixtures being most preferred.
• Cyclisation may be effected by any suitable reagent or combination of reagents.
• Suitable combinations of reagents include a coupling reagent such as benzotriazole-1-yl-oxy-tris-pyrrolidino-phosphonium hexafluorophosphate
• pyBOP benzotriazole-1 -yl-oxy-tris-(dimethylamino)-phosphonium hexafluorophosphate
• BOP benzotriazole-1 -yl-oxy-tris-(dimethylamino)-phosphonium hexafluorophosphate
• HBTU 2-(1 H-benzotriazole-1-yl)-1 , 1 ,3,3- tetramethyluronium hexafluorophosphate
• TBTU 2-(1H-benzotriazole-1-yl)- 1 ,1 ,3,3-tetramethyluronium tetrafluoroborate
• DCC dicyclohexylcarbodiimide
• CDI 1 ,1'-carbonyl-diimidazole
• a base such as di- /sopropylethylamine (DIPEA) or triethylamine.
• DIPEA di- /s
• the cyclisation process may be performed in the presence of a coupling reagent, a base and N- hydroxybenzotriazole (HOBt).
• a coupling reagent e.g., a base and N- hydroxybenzotriazole (HOBt).
• HOBt N- hydroxybenzotriazole
• the cyclisation process is carried out with pyBOP, HOBt and DIPEA.
• the compound of formula (III) may be prepared by sequentially coupling a compound of formula (IV)
• B 3 and B 4 represent the skeleton of an ⁇ -amino acid
• P is hydrogen or a carboxyl protecting group or a linker group
• T 3 represents an activating group, amine protecting group or linker group, with two suitably protected ⁇ -amino acids in a conventional manner.
• the compound of formula (IV) may be prepared by any suitable method known to those skilled in the art.
• compounds of formula (IV) may be prepared by reacting a compound of formula (V) with a compound of formula (VI) under Mitsunobu conditions,
• the compound of formula (IV) may be prepared by reacting a compound of formula (VII) with a compound of formula (VIII),
• B 3 and B 4 represent the skeleton of an ⁇ -amino acid
• P is a carboxyl protecting group or a linker group
• P ' is an amine protecting group
• the condensation reaction is followed by the reduction of the resulting imine, for example with sodium cyanoborohydride, and protection of the resulting secondary amine with a suitable amine protecting group T 3 .
• the present invention provides a compound of formula (II),
• each of B ⁇ B 2 , B 3 and B 4 independently represent the skeleton of an ⁇ -amino acid, D.,, D 2 and D 3 each independently represent carbonyl or methylene, with the proviso that only one of the groups selected from D ⁇ D 2 , and D 3 can be methylene, and T 1 f T 2 and T 3 , which are optionally present, each independently represent hydrogen or an organic substituent or an activating group, an amine protecting group or a linker group, with the proviso that the compound of formula (II) is not selected from 6- [(4-nitrophenyl)methyl]-1 ,4,7, 10-tetraazacyclododecane-2,5,8-trione, 6-[(4- nitrophenyl)methyl]-10-(trifluoroacetyl)-1 ,4,7, 10-tetraazacyclododecane-2,5,8- trione and 5-[(4-nitrophenyl)methyl]-3,6,9-
• the compound of formula (II) is cyclic ⁇ Aoda-Trp- ⁇ -[CH 2 N(ONS)]-lle- D-Pro ⁇ .
• Cyclic ⁇ Aoda-Trp- ⁇ -[CH 2 N(ONS)]-lle-D-Pro ⁇ was assessed for activity against Trypanosoma brucei, strain S427.
• the test was carried out against the bloodstream trypomastigote form (extracellular) grown in culture (in vitro).
• the medium used for growth was HMI- 18 supplemented with 10% heat inactivated foetal calf serum at 37°C in an 5% CO 2 / air mixture.
• Parasites were incubated in medium containing drug for 72 hours. At the endpoint, the number of parasites in the control untreated culture was compared with the number in drug treated cultures and a % inhibition calculated. A standard pentamidine isethionate was included for comparison.
• Cyclic ⁇ Aoda-Trp- ⁇ -[CH 2 N(ONS)]-lle-D-Pro ⁇ was found to have an ED 50 of 2.0 ( ⁇ g ml 1 ).
• LCMS data was obtained on a Hewlett Packard HP1050 instrument using an ABZ+PLUS column (330 x 4.6 mm) with a supelcosil packing (3 ⁇ m particle size).
• Mass spectra were obtained on a Platform Series II spectrometer using electrospray ionisation in +ve and - mode.
• Triethylamine (1.97 ml, 14.1 mmol) was added to a stirred suspension of Phe- O'Bu HCI (2.00 g, 7.80 mmol) in dry dichloromethane (100 ml) at RT. After 10 min the mixture was cooled to 0°C; and a solution, of 2-nitrophenylsulfonyl chloride (4.67g, 21.1 mmol) in dichloromethane (50 ml) was added dropwise and the reaction mixture then stirred for 1 h at 0°C and for 24 h at RT.

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