EP1701975A1 - Nonnatural c-linked carbo-beta-peptides with robust secondary structures - Google Patents

Abstract

The present invention provides novel nonnatural C-linked carbo-β-peptides with robust secondary structures, which comprises the synthesis of a new class of β-peptides called C-linked carbo-β-peptides, most of which are favorably disposed for the formation of stable helical structures. Formula (I): wherein n= 0, 1, 2, 3 . . .; R= H, Boc, Cbz, Fmoc, acetyl or salts such as HC1, TFA and others; R1 = -O alkyl, -O-aralkyl, -amine, alkylamine, aryalkyl maine; R2 = R3 = R4 = R5 = H; R2 = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R3 = R4 = R5 = H; R3 = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R2 = R4 = R5 = H; R4 = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R2 = R3 = R5 = H; R5 = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R2 = R3 = R4 = H; R2 = R4 = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R3 = R5 = H; R3 = R5 = sugar or hydroxyl alkyl, amino alkyl/thioalkyl, R2 = R4 = H; R2 = R5 = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R3 = R4 = H; R3 = R4 = sugar or hydroxyl alkyl, amino alkyl/thioalkyl, R2 = R5 = H; R2 = R3 = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R4 = R5 = H; R4 = R5 = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R2 = R3 = H.

Description

NONNATURAL C-LINKED CA BO-β-PEPTEDES WITH ROBUST SECONDARY STRUCTURES FIELD OF THE INVENTION The present invention relates to Novel nonnatural C-linked carbo-β-peptides with robust secondary structures and process for the preparation of the said compounds. The novel β-peptides are derived from the coupling of a variety of C-linked carbohydrate β-amino acids. These β-peptides contain a variety of carbohydrate moieties on the backbone of β-peptide as carbohydrate recognition sites. The thus made β-peptides have shown stable helical structures. BACKGROUND OF THE INVENTION Reference is made to J. Am. Chem. Soα, 116, 1054-1062 (1994), by Gell an et al, wherein the β-and γ-amino acids were postulated to fold in the same manner as α-amino acids through intramolecular hydrogen bonding. In 1996, two groups of scientists, one led by Seebach et al and another by Gellman et al reported the first synthesis of β-peptides showing well-defined secondary structures. Reference may be made to Helv. Chim. Acta. 79, 913-941 and 2043-2066 (1996), wherein it was the first group worked on the synthesis of β-hexapeptide consisting of acyclic β- amino acid monomers and explored for the secondary structures along with effects of residue variation on the secondary structures. Reference is made to J. Am. Chem. Soc, 118, 13071-72 (1996), wherein Gellman group worked on synthesis of β-peptides containing a cyclohexane 1,2-amino acid (ACHC) as β-amino acid monomer to derive a 14-helical structure. Reference may further be made to Nature 387, 381 (1997), wherein cyclopentane amino acid (ACPC) gave 12-helical structure. Reference is made to Helv. Chim. Acta. 81, 932 (1998), wherein Seebach' s group worked on β²-β³ mixed hexapeptide which exhibited a 12/10/12 helix (10/12 helix) while reference is also made to Helv. Chim. Acta. 81, 2218-2243(1998), wherein β³'³, β^2,2 amino acids and their β-peptides were prepared, while β³'³ have shown 8-helix. Reference is made to Angew. Chem. Int. Ed , 41, 230-253 (2002); Chem. Rev. 102,

491-514 (2002); Chem. Eur. J., 8, 4366-4376 (2002), which reviewed about a new class of 'sugar amino acids' wherein both the acid and amine components are installed on the carbohydrate frame and a variety of α, β, γ, δ, -sugar amino acids were prepared and converted into the corresponding peptides of a variety of secondary structures and biological activities. OBJECTS OF THE INVENTION The main object of the present invention is to synthesize a new class of C-linked carbo β-peptides. Other object is to synthesize a new class of β-amino acids having carbohydrate moieties as side chains. Yet another object is to convert the thus made newer C-linked carbo β-amino acids into the corresponding C-linked carbo β-peptides as a new class of β-peptides. A further object is to synthesise these new C-linked carbo β-peptides as proteolytically stable peptide molecules. The other object to synthesise the new class of C-linked carbo β-peptides is to enhance the water solubility and stability. The objective for the synthesis of these new C-linked carbo β-peptides is to enhance the carbohydrate recognition sites in the peptides thus made. Another object is to enhance the activity of the thus made peptides for their biological profile and develop them into anti-cancer, anti-microbial and other therapeutic class agents. Another object of the present invention provides novel processes for the synthesis of said novel β-amino acids and β-peptides that would exhibit interesting biological activity.

These synthetic process routes utilize commercial reagents and facilitate large scale preparation, and provide the new class of C-linked carbo β-peptides in sufficient quantities for further biological evaluation. Another object of the present invention is to use chirality as the controlling point in giving stable secondary structures. C-Linked carbo β-amino acids, epimeric at the amine center for making the C-linked carbo β-peptides having stable secondary structures. Another object of the present invention is to synthesize C-linked β-peptides with C- linked carbo β-amino acid with D configuration, C-linked β-amino acids with L- configuration and mixed peptides with D and L-C- inked carbo-β-amino acids. SUMMARY OF THE INVENTION Accordingly the present invention provides novel nonnatural C-linked carbo-β- peptides with robust secondary structures, which comprises of the synthesis of a new class of β-peptides called C-linked carbo-β-peptides, most of which are favorably disposed for the formation of stable helical structures. In one embodiment of the invention, synthesis of a new class of β-peptides is provided, since β-amino acids are part structures of several biologically active compounds. Another embodiment of the invention deals with synthesis of C-linked carbo β- amino acids since several sugar amino acids are part structures of biologically active compounds. In yet another embodiment, the new β-peptides with carbohydrate moieties^' find use as biologically active carbo-β-peptides, the rationale for synthesis of such new class of C- linked carbo β-peptides is to derive small bioactive peptides reported in this invention are as below: 1) β-peptides derived from β-amino acids unlike peptides from α-amino acids are metabolically more stable, since they are non-natural. 2) The β-peptides thus made in this invention due to the presence of carbohydrate structures would act as recognition sites. 3) The presence of carbohydrate moieties on the β-peptide chain would enhance the solubilities of these peptides tremendously, thereby facilitating the transportation. 4) The β-peptides thus made from C-linked carbo β-amino acids would impart a high degree of amphiphilicity due to the hydrophilic nature of the β-peptides. 5) The β-peptides with C-linked carbo β-amino acids thus made would show their peptide activity and can possess other favorable characters which are imparted such as enzymatic stability and transport profiles. 6) β-peptides thus made from C-linked carbo β-amino acids due to presence of both carbohydrate and peptide moieties in their skeletons, would enhance process of peptide based drug discovery, devoid of the problems associated with solubilities of peptide based active compounds. In addition, it imparts proteolytic tolerance to these compounds. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 represents the structure of poly β-alanine, wherein the hydrogen bonding is depicted indicating a variety of helical structures possible. Figure 2 represents Circular Dichroism (CD) plot for 43 in MeOH and its simulated model, where sugar is replaced with methyl for clarity and clear visualization. Figure 3 represents Circular Dichroism (CD) plot for 38 in MeOH and its simulated mode', where sugar is replaced with methyl for clarity and clear visualization. Figure 4 represents Circular Dichroism (CD) plot for 41 in MeOH and its simulated model, where sugar is replaced with methyl for clarity and clear visualization. Figure 5 represents Circular Dichroism (CD) plot for 42 in MeOH and its simulated model, where sugar is replaced with methyl for clarity and clear visualization. Figure 6 represents Circular Dichroism (CD) plot for 23 in MeOH and its simulated model, where sugar is replaced with methyl for clarity and clear visualization. Figure 7 represents Circular Dichroism (CD) plot for 26 in MeOH and its simulated model, where sugar is replaced with methyl for clarity and clear visualization. Figure 8 represents Circular Dichroism (CD) plot for 27 in MeOH and its simulated model, where sugar is replaced with methyl for clarity and clear visualization. Figure 9 represents Circular Dichroism (CD) plot for 52 in MeOH and its simulated model, where sugar is replaced with methyl for clarity and clear visualization. DETAILED DESCRIPTION OF THE INVENTION The present invention is related to the synthesis of C-linked carbo- β-peptides. Some of which favor the formation of novel helical secondary structures such as 12, 14 or 10/12 helices. The presence of carbohydrate moiety on the β-peptide backbone is desirable since, it helps not only as sugar recognition center in the new β-peptides, but also attributes amphiphilicity due to hydrophilic nature. The synthetic protocol developed in the present invention is suitable for the synthesis of β-peptides with the following formula I.

Formula I n = 0 ',J 1 *,3 2 * , 3 R= H, Boc, Cbz, Fmoc, acetyl or salts such as HCl, TFA and others R¹⁼ -O alkyl, -O-aralkyl₃ -amine, alkylamine, aryalkyl maine R² = R³ = R⁴= R⁵ =H R² = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R³ = R⁴= R^s =H R³ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R² = R⁴ = R⁵ =H R⁴= sugar or hydroxy alkyl, amino alkyl/thioalkyl, R² = R³ = R⁵ =H R⁵= sugar or hydroxy alkyl, amino alkyl/thioalkyl, R² = R³ = R⁴ =H R² = R⁴ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R³ = R⁵ =H R³ = R⁵ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R² = R⁴ =H R² = R⁵ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R³ = R⁴ =H R³ = R⁴ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R² = ^D =H R² = R³ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R⁴ = R⁵ =H R⁴ = R³ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R² = R³ =H Sugars can be monosaccharide pentoses such as D-xylo, O-ribo, O-Iyxo, D-ara or the L-sugars such as L-xyl, h-rib, L-lyxo, L-ara in furanoside or pyranoside form; hexoses such as D-and -glc, D-and L-gal, D-and h-man, D-and L-guI, D-and L-all, etc. in furanoside/pyranoside form; disaccharides such as lactose, maltose, cellobiose etc.; fully protected as acetates, benzoates, allyl or aralkyl ethers, alkylidene dioxolane derivatives, thio derivatives or totally unprotected sugars, D and L sugars in furanoside/pyranoside form having heterocyclic bases such as adenine, guanine, thymidine, cytosine or unnatural bases or heterocyclics having one or more than one heteroatoms such as O/N/S both in 5 and 6 membered rings, dexoy sugars/amino sugars natural/non-natural, rare sugars and higher sugars, bifunctional sugar amino acids. The present invention provides a new class of C-linked carbo β-peptides having basic structure as depicted in structural formula I. The main advantage of the present invention is that it allows construction of C- linked carbo β-peptides hitherto unknown class, with secondary structures of high stability, the formation of the proposed secondary structures is well controlled through the variation of chirality at amine bearing carbon stereo centre of C-linked β-amino acid monomer. Since the non-natural β-peptides can be synthesized with well defined and stable secondary structures, they can mimic secondary structures of natural protein and thereby disrupt biological interactions of biopolymers (proteins). Since, these peptides adopt stable secondary structures through chirality control, they are well suited for molecular design.

Further to the invention, the C-linked carbo β-peptides are useful as base molecules to synthesize an array of peptide libraries with varying the sequence of β-amino acid carbohydrate moieties, functional groups and the like. Since the chirality plays a prominent role in deriving the secondary structures altering the substituent accordingly do not substantially disturb the secondary structures thus can be advantageously utilized to build vast array of C-linked carbo β-peptide with a wide variety of substituents with a similar stable secondary structures in solution. Helices in β-peptides: Initial molecular model studies indicated that oligomers of β- amino acid (β-peptides) are well suited for adoption of compact secondary structures stabilized by intramolecular hydrogen bonds. Fig. 6 shows the hydrogen bonds that define the helices obtained for a tetrapeptide. These are referred to as 10/12/10 helices, (10, 12, 10 refer to the number of bonds between the hydrogen bonding atoms) nomenclature was derived from N- terminal amide hydrogen towards the C-terminal carbonyl group. The tetrapeptide in Fig. 3 has been shown to adopt a 12/10 helical structure with intertwined hydrogen bonded secondary structure. The rigidity of the structure is due to the stereochemical and electronic contributing aspects of the sugar moiety in the tetrapeptide. Incorporation of the sugar motifs in the backbone carbon of β- amino acid provide not only substantial bulkyness but also helps in assembly of very small peptides, even trimers/tetramers, display secondary structure. Schemes 1 and 2 exemplify preferred preparative method of the invention that provide the amino acid monomers 3 to 10. Sche e 1

The aldehyde 1 was converted to α, β-unsaturated ester 2 example 1, part 1. Michael addition reaction on 2 with benzyl amine, dibenzyl amine and other amines of the like under basic conditions such as TBAF, DBU, DBN, Hunig's base, triethyl amine or other suitable organic bases or metal alkoxides in suitable solvents such as THF or other solvents to get the β-amino acid 3 (Tetrahedron: Asymm. (2002) 13, 21-24). See example 1, part 2 method A, for exemplary reaction conditions. The compound thus reported in the invention is a single enantiomer. For generation of 4 a related approach as reported was adopted, for instance (J. Org. Chem. 2001, 16, 1065) to get the mixture of 3 and 4, according to the conditions exemplified in example 1, part 2 method B. Amino acids represented by the formula 3 and 4 are subjected to hydrogenolysis in presence of Pd-C in suitable solvents such as methanol under hydrogen atmosphere to give 5 and 8 respectively as exemplified in example 1, part 3 and part 5 respectively, which were used as such for further reactions. As exemplified in example 1, part 3 and part 7, 3 and 4 are subjected to Scheme 2 catalytic hydrogenation and subsequently without isolation exposed to (Boc)₂O under basic

Synthesis of peptides using (S)-amino acids Scheme 3 exemplifies a preferred preparative method of the invention that provides compounds of formula 11, 14, 17, 18 and 19 representing dϊ, tetra, hexa, octa and tri C- linked carbo β-peptides. Scheme 3

Thus in scheme 3, the monomers 5 and 6 are coupled by conventional reagents such as dicyclohexyl carbodiimide / N-hydroxy succinimide (DCC/HoBt) or 1- ethyl -3-(3'- dimethyl amino prepyl) carbodiimide hydrochloride/N-hydroxy benztriazole (EDCI/HOBt) in solvent phase coupling procedures (see, example Bodanszky, M-; Bodanszky, A. The practice of peptide synthesis; Springer Nsrlag; New York, 1984) in suitable solvents such as CH₂CI₂ to result in a dideptide 11. For exemplary reaction conditions for the preparation of 11 see example 2, part 1. Dipeptide 11 was treated with an organic acid like TFA and the like in suitable solvents for eg; CH₂C1₂ and the like to provide salt 12 as exemplified in example 2, part 2. Similarly 11 was also subjected to base induced hydrolysis in presence of suitable base like NaOH and the like in acceptable solvents like MeOH to furnish an unprotected acid 13. For detailed experimental discussion see example 2, part 3. Further synthesis of a tetrapeptide was achieved upon coupling of 12 and 13 in presence of conventional reagents like EDCI/HOBt/DIPEA in suitable solvents for eg; CH₂C1₂ to yield 14 as exemplified in example 2, part 4. Tetrapeptide 14 was subsequently converted to free acid 15 under basic hydrolysis conditions with conventional reagents like NaOH in- methanol. See example 2, part 5. Also 14 was further exposed to TFA in CH₂C1₂ to deblock the Boc protecting group and the same was isolated as TFA salt 16, as exemplified in example 2, part 6.

Further preparative methods of other oligomers is depicted in Scheme 3. For eg; coupling of 15 with 12 under the above standard reaction conditions (EDCI/HOBt/DIPEA, CH₂CI₂, DMF) respited in the hexapeptide 17. For experimental conditions see example 2, part 7. Similarly coupling of 15 with 16 under the conventional peptide coupling reaction conditions as described above, with EDCI in presence of solvents like CH₂C1₂: DMF in ratio as suitable enough for the reaction to result in the product octamer 18, as exemplified in example 2 part 8. A similar preparative description was made use for the preparation of tri peptide 19 from 13 and 7, under the above said reaction conditions of EDCI/HOBt in solvents conventionally used in peptide coupling such as CH2CI₂, as exemplified in example 2 part 9. Synthesis of peptides using S and R amino acids Scheme 4 exemplifies a preferred preparative method of the invention that provides compounds of formula 20, 23, 26, 27 and 28 representing di, tetra, hexa, octa and tri C- linked carbo β-peptides. Scheme 4

Thus in Scheme 4, the monomers 8 and 6 are coupled by conventional reagents such as dicyclohexyl carbodiimide / N-hydroxy succinimide (DCC/HoBt) or 1- ethyl -3-(3'- dimethyl amino prepyl) carbodiimide hydrochloride/N-hydroxy benztriazole (EDCI/HOBt) in solvent phase coupling procedures (see, example Bodanszky, M-; Bodanszky, A. The practice of peptide synthesis; Springer Nerlag; New York, 1984) in suitable solvents such as CH₂CI₂ to result in a dideptide 20. For exemplary reaction conditions for the preparation of 20 see example 3, part 1.

Scheme 4 (Contd.)

28 Dipeptide 20 was treated with an organic acid like TFA and the like in suitable solvents for eg; CH₂C1₂ and the like to provide salt 21 as exemplified in example 3, part 2.Similarly 20 was also subjected to base induced hydrolysis in presence of suitable base like

NaOH and the like in acceptable solvents like MeOH to furnish an unprotected acid 22. For detailed experimental discussion see example 3, part 3. Further synthesis of a tetrapeptide was achieved upon coupling of 21 and 22 in presence of conventional reagents like EDCI HOBt/DIPEA in suitable solvents for eg; CH₂CI₂ to yield 23 as exemplified in example 3, part 4. Tetrapeptide 23 was subsequently converted to free acid 24 under basic hydrolysis conditions with conventional reagents like NaOH in methanol. See example 3, part 5. Also 23 was further exposed to TFA in CH₂C1₂ to deblock the Boc protecting group and the same was isolated as TFA salt 25, as exemplified in example 3, part 6. Further preparative methods of other oligomers is depicted in Scheme 4. For eg; coupling of 24 with 21 under the above standard reaction conditions (EDCI/HOBt/DIPEA, CH₂C1₂, DMF) resulted in the hexapeptide 26. For experimental conditions see example 3, part 7. Similarly coupling of 24 with 25 under the conventional peptide coupling reaction conditions as described above, with EDCI in presence of solvents like CH2CI2: DMF in ratio as suitable enough for the reaction to result in the product octamer 27, as exemplified in example 3 part 8. A similar preparative description was made use for a the preparation of tri peptide 28 from 22 and 7, under the above said reaction conditions of EDCI/HOBt in solvents conventionally used in peptide coupling such as CH₂C1₂, as exemplified in example 3 part 9. Synthesis of peptides from R amino acids Scheme 5 exemplifies a preferred preparative method of the invention that provides compounds of formula 29, 32 and 34 representing di, tetra and hexa C-linked carbo β- peptides. Thus in Scheme 5, the monomers 8 and 9 are coupled by conventional reagents such as dicyclohexyl carbodiimide / N-hydroxy succinimide (DCC/HoBt) or 1- ethyl -3- (3'- dimethyl amino prepyl) carbodiimide hydrochloride/N-hydroxy benztriazole (EDCI/HOBt) in solvent phase coupling procedures (see, example Bodanszky, M-;

Bodanszky, A. The practice of peptide synthesis; Springer Verlag; New York, 1984) in suitable solvents such as CH₂C1₂ to result in a dideptide 29. For exemplary reaction conditions for the preparation of 29 see example 4, part 1. Dipeptide 29 was treated with an organic acid like TFA and the like in suitable solvents for eg; CH₂CI2 and the like to provide salt 30 as exemplified in example 4, part 2. Similarly 29 was also subjected to base induced hydrolysis in presence of suitable base like NaOH and the like in an acceptable solvents like MeOH to furnish an unprotected acid 31. For detailed experimental discussion see example 4, part 3. Further synthesis of a tetrapeptide was achieved upon coupling of 30 and 31 in the presence of conventional reagents like EDCI/HOBt/DIPEA in suitable solvents for eg; CH₂C1₂ to yield 32 as exemplified in example 4, part 4. Tetrapeptide 32 was subsequently converted to free acid 33 under basic hydrolysis conditions with conventional reagents like NaOH in methanol. See example 4, part 5. Further preparative methods of other oligomers is depicted in Scheme 5. For eg; coupling of 33 with 30 under the above standard reaction conditions (EDCI/HOBt/DIPEA, CH₂C1₂, ^ F) resulted in the hexapeptide 34. For experimental conditions see example 4, part 6.

Scheme 5

Synthesis peptides from R and S amino acids Scheme 6 exemplifies a preferred preparative method of the ⁱnvention that provides compounds of formula 35, 38, 41, 42 and 43 representing di, tetra, hexa, octa and tri C- linked carbo β-peptides. Scheme 6

Thus in Scheme 6, the monomers 5 and 9 are coupled by conventional reagents such as dicyclohexyl carbodiimide / N-hydroxy succinimide (DCC/HoBt) or 1- ethyl -3-(3'- dimethyl amino prepyl) carbodiimide hydrochloride/N-hydroxy benztriazole (EDCI/HOBt) in solvent phase coupling procedures (see, example Bodanszky, M-; Bodanszky, A. The practice of peptide synthesis; Springer Verlag; New York, 1984) in suitable solvents such as CH₂C1₂ to result in a dideptide 35. For exemplary reaction conditions for the preparation of 35 see example 5, part 1. Dipeptide 35 was treated with an organic acid like TFA and the like in suitable solvents for eg; CH₂CI₂ and the like to provide salt 36 as exemplified in example 5, part 2. Similarly 35 was also subjected to base induced hydrolysis in presence of suitable base like NaOH and the like in an acceptable solvents like MeOH to furnish an unprotected acid 37. For detailed experimental discussion see example 5, part 3. Further synthesis of a tetrapeptide was achieved upon coupling of 36 and 37 in presence of conventional reagents liku EDCI/HOE.t/DIPEA in suitable solvents for . eg; CH₂C1₂ to yield 38 as exemplified in example 5, part 4. Tetrapeptide 38 was subsequently converted to free acid 39 under basic hydrolysis conditions with conventional reagents like NaOH in methanol. See example 5, part 5. Also 38 was further exposed to TFA in CH C1₂ to deblock the Boc protecting group and the same was isolated as TFA salt 40, as exemplified in example 5, part 6. Scheme 6 (Contd.)

Further preparative methods of other oligomers is depicted in Scheme 6. For eg; coupling of 40 with 36 under the above standard reaction conditions (EDCI/HOBt/DIPEA, CH₂Cl₂, DMF) resulted in the hexapeptide 41. For experimental ^conditions see example 5, part 7. Similarly coupling of 39 with 40 under the conventional peptide coupling reaction conditions as described above, with EDCI in presence of solvents like CH₂C1₂: DMF in ratio as suitable enough for the reaction to result in the product octamer 42, as exemplified in example 5 part 8. Similarly coupling of 37 with 10 under the conventional peptide coupling reaction conditions as described above, with EDCI in presence of solvents like CH2CI2 resulted in the product trimer 43, as exemplified in example 5 part 9 (Scheme 6). Further synthesis of a tetrapeptide 44 was achieved on coupling of 22 and 36 in presence of conventional reagents like EDCI/HOBt DIPEA in suitable solvents for eg; CH₂C1₂ to yield 44 as exemplified in example 6, part 1 (Scheme 7). Similarly, as exemplified in example 6, part 2, tetrapeptide 45 was achieved on coupling of 37 and 21 in presence of conventional reagents like EDCI/HOBt/DIPEA in suitable solvents for eg; CH₂C1₂ to yield 45. Scheme 7

Scheme 8 exemplifies a preferred preparative method of the invention that provides compounds of formula 47, 50 and 52 representing mixed di, tetra and hexa C-linked carbo β-peptides made from 6 and β-alanine methyl ester 46. Thus in Scheme 8, the monomers 6 and 46 are coupled by conventional reagents such as dicyclohexyl carbodiimide / N- hydroxy succinimide (DCC/HoBt) in suitable solvents such as CH₂C1₂ to result in a dideptide 47. For exemplary reaction conditions for the preparation of 47 see example 7, part 1. Dipeptide 47 was treated with an organic acid like TFA and the like in suitable solvents for eg; CH₂CI₂ and the like to provide salt 48 as exemplified in example 7, part 2. Similarly 47 was also subjected to base induced hydrolysis in presence of suitable base like NaOH and the like in an acceptable solvents like MeOH to furnish an unprotected acid 49. For detailed experimental discussion see example 7, part 3. Further synthesis of a tetrapeptide Wu.s achieved upon coupling of 48 and 49 in the presence of conventional reagents like EDCI/HOBt/DIPEA in suitable solvents for eg; CH₂C1₂ to yield 50 as exemplified in example 7, part 4. Tetrapeptide 50 was subsequently converted to free acid 51 under basic hydrolysis conditions with conventional reagents like NaOH in methanol. See example 7, part 5. Scheme 8

Further preparative methods of other oligomers is shown in Scheme 8. For eg; coupling of 48 with 51 uncier above standard reaction conditions {EDCI/HOBt/DIPEA, CH₂CI₂, DMF) resulted in hexapeptide 52. For experimental conditions see example 7, part 6. As exemplified in the Schemes 1-8, the synthetic protocols developed by this invention, numerous C-linked carbo β-peptide class of compounds represented by formula I can be synthesised. This new class of C-linked carbo β-peptides prepared by the method of invention are useful for numerous therapeutic applications. As exemplified in the preparative procedures, carbo β-peptide class of compounds described in here and represented by formula I can be readily prepared. As described in the proeceding secions the compounds that are prepared in the present invention are useful for numerous therapeutic applications. In need of treatment, these compounds can be administered by a variety of ways, such as orally, parentally, intravenously, subcutaneously and other routes. Conformational Analysis 1. NMR Spectroscopy: Molecular conformations were investigated by NMR spectroscopy. Such studies were carried out in about 2-8 mM solution in CDCl_3j DMSO-^6, CD₃OH CD₃OD or pyridine-α5. Two-dimensional (2-D) experiments like TOCSY (Cavanagh. J; Fairbrother. W. J; Palmer, N. J; Protein NMR Spectroscopy; Academic Press San Diego, 1996) and ROESY (Wuthrich K; NMR of Proteins and Nucleic Acids, Wiley, New York, 1986) were obtained on NARIAN -INONA 500 MHz spectrometer at 30° C using standard pulse sequences, provided by NARIAN using phase sensitive (States, D.J.; Haberkorn, RA; Ruben, D. J, J. Magn. Reson 48, 286-292, 1982) experiments. Data were processed with Varian NNMR 6. lb software. The data for these experiments were collected as 384 x 2048 matrix, using 8-16 scans, per ti, increment. The data were zero filled and Fourier transformed as 2k x 4k data matrix. Almost all the resonances in the backbone were very highly resolved in CDC1₃ and could be assigned with the help of TOCSY and ROESY experiments. TOCSY provided the assignments within the same residue and ROESY provided sequential assignments. In these oligomers the N-terminal amides show NOE with intra residue C_αH proton alone, and donot show any inter residue NH / CαH NOE like other amides. This assignment has further been supported from the NOE between the amide and Boc group. Also C_a protons at C-terminal residue has been identified from the presence of NOE only with the self-amide NH. Information on Hydrogen bonding a) Solvent titration Studies: In non-polar solvents, titration with a polar solvent is used to assess stability of structure. Intra-molecularly H-bonded amide proton chemical shifts in CDC1₃ do not change much when a polar hydrogen bond promoting solvent like DMSO-c 6 is added upto 33% v/v. Amide protons, which are not intramolecularly hydrogen bonded, form hydrogen bond with DMSO-d6 and their resonances show large shifts towards downfield. b) Amide proton exchange: Amide proton exchange is usually used for getting information on intramolecular hydrogen bonding in peptides, which permits to assess conformational stability of peptides. Presence of intramolecular hydrogen bonds results in reduced rate of NH / ND exchange. The amide protons of the peptide, which are forming intramolecular hydrogen bonding exchanges very slowly in CD₃OD solution, even upto 2-3 days, where as non-hydrogen bonded amides can exchange very fast, sometimes even with in few minutes. c) Variable Temperature experiments: In DMSO- 6, temperature coefficients of amide proton chemical shift (Δδ/ΔT in ppb/°K) is used as a signature of intra-molecular hydrogen bond. By varying temperature, amides chemical shifts show small magnitude of temperature coefficients, when they participate in intramolecular hydrogen bonds. Those amides, which are not taking part in hydrogen bonding, show large magnitude of temperature coefficients. 2. Circular Dichroism Spectroscopy: The circular dichroism (CD) data in the UN region was obtained on JASCO-510 and JASCO-715 instrument at room temperature (nominally 20°C). The ellipticities are reported as mean residue molar ellipticity, which is obtained by normalizing for the total number of amide chromophores present in the oligomer. 3. Molecular Dynamics/Mechanics studies: Restrained molecular dynamics data was used to generate 20 low energy conformation. The back bone heavy atoms superimposed rather well (RMSD < A⁰). However the C terminal did show fraying. Side chains did show a larger degree of freedom. Results and Discussions: - Tetrapeptide-23, Hexapeptide-26 and Octapeptide-27- Solvent titration studies by adding upto 33% v/v DMSO-d6 in CDC1₃ show that apart from second residue amide [ΝH (2)] all amide protons are hydrogen bonded in both peptides as they show very small (< 0.6ppm) change in their chemical shifts. This is further supported by a very large range for amide chemical shifts (about 3 ppm for 23, 26 and 27) as well as their very low field shifts (£ NH for two amides in 26, four amides in 26 and six amides in 27 are above 7.0 ppm). C_αH protons also show a very big chemical shift dispersion of about 0.7,0.8 and 0.75ppm respectively for 23, 26 and 27. The presence of ³JcαH-cpH of about 5 Hz or below and 10 Hz and above very ,clearly demonstrates that θ take only g/t conformations. Molecules take primarily a single value of θ = 60°, which is further supported by strong inter residue NOE The ROESY spectra show very distinctive NOE's corresponding to the 10/12/10 helices. Specially noteworthy are the medium backbone NOE between C_/?H(2) with NH (4) and C_a (pro-R) (4) NOE's in 23, qualifying the 12-membered hydrogen bond. Where as in 23 and 26 several of these NOE propagate along the helix. For 26 strong C _?H (2) / NH (4) and QgH (2) / (4) as well as C/>H(4) / NH (6) and C fl(4) / C_αH₍p_ro-Λ) (6) NOE's are seen. For 27 in addition to the NOE's mentioned for 1 and 2, we observe jH (6) / NH (8) and Cpϋ(6) I C_αH (p_ro-_R) (8) NOE peaks. In addition, characteristic weak NOE due to 10-membered hydrogen bonds of the helix between NH (1) / NH (2), NH (3) /NH (4), NH (5) / NH (6) and NH (7) / NH (8) are observed for 27. Because of the smaller size of 26 only NH (1) / NH (2), NH (3) / NH (4) and NH (5) / NH (6) and for 23 NH (1) / NH (2) and NH (3) / NH (4) inter residue NOE's are observed. In 23, 26 and 27 despite the fact that Boc amide is the first residue, it participates in H-bonding and thus confirms their remarkable stability. In short α-helices the ends are frayed in solution. These chirality-controlled oligomers show that the sugar containing -aminoacids lead to very well defined helices even for peptides containing only four residues. Orientation of sugar rings with respect to backbone is well characterized. Excluding residue 2 (R(2)), ³Jce_H-c_4H is large ( ~10 Hz ), corresponding to dihedral angle C_?H-C_/rC₄-

GiΗ (χϊ) of about 180°. Such an orientation is further supported by NOE's of NH / C₄H and NH / JA p_m-_R). It leaves the sugar ring planes alternately pointing in opposite direction

(opposite to the sense of the screw axis of the helix). The methoxy groups of the odd residues point towards the C terminal, where as those for the even residues, excluding the second residue, points towards the N terminal. For residue 2 (R (2)), the ³JcpH-c4H = 6.0,

5.8 and 6.2 Hz for 23, 26 and 27. This indicates a predominance of conformation with torsion angle | C₅H-C_/ C -C₄H j= 60°. The presence of strong NOE of C₄H / CJ _ro-_S) and medium NOEs of C₄H / C_αH(p_rø-s) , C₃H / C_aE<p_ro-R) and C₃H / C_aU _ro-s) enabled us to fix this angle as -60°. Couplings for sugar ring are all very small. Vicinal coupling constants ³Jci_H-c2_H ~ 3 Hz, ³Jc2H-c3H ~ 0 Hz and ³Jc_3H-c_4H ~ 4 Hz correspond to a sugar pucker of ³T₂. Strong NOE between Me^.^ /CiH and Me _ro._R I C₂H as well as weak Me^s_j / C H NOE show that isopropylidene ring exists in envelop conformation. These observations are also in conformity with sugar unit structure in several other molecules with C-C glycosidic linkages. The data in DMSO-d6 was also well understood and almost all the NOE's discussed above were obtained. Though the chemical shift dispersion was not as much as in CDC1₃ and also some of the couplings indicate little more flexibility in the structure. However, the 10/ 12/ 10 helix is very well preserved. Tripeptide-43, Tetrapeptide-38, Hexapeptide-41 and Octapeptide-42: The solvent titration studies in CDC1₃ and variable temperature studies in DMSO-d6 very clearly show that for 43 and 38 amide protons of residue S(2) and R(3) are hydrogen bonded. For 41 the presence of four hydrogen bonds for amide protons, corresponding to S(2), R(3), S(4) and R(5) is observed and for 42 the presence of six hydrogen bonds for amide protons S(2), R(3), S(4), R(5), S(6)is observed. The large amide chemical shifts range (e.g., about 3.57 ppm for 7) and low field shifts of several of them (δ NH upto 8.92 ppm for 7) further support the presence of large number of hydrogen bonds in this family of molecules. The C_αH protons also show very large dispersion of 0.52, 0.93, 1.08 and 0.92 ppm for 43, 38, 41 and 42 respectively, additionally confirming a well defined structure for them. Very large (>10 Hz) and very small (often < 5 Hz) ³JcάH-cβκ values very clearly show that molecule takes primarily a predominant single conformation with θ = 60°. This is further supported by strong inter residue NOE between NH / C_aH _ro-R), C jH / CJϊrpro-S)- The ROESY spectra show characteristic NOE cross peaks corresponding to the presence of 12/10 helices in 43, 38 and 12/10/12/10 helix in 41 and 12/10/12/10/12/10 helix in 42. Strong strength of NOE's of ^H (1) / NH (3) and QeH (1) / CαHo»o-Λ) (3) and weak NH (2) / NH (3) NOE, in addition to presence of two hydrogen bonded amides shows the presence of 12/10 helices in 43 and 38. For 41 in addition to above NOE's, strong intensity NOE's C £ϊ(3) / NH (5) and C_βϋ (3) / C_aU^o-S (5) and weak intensity NH (4) / NH (5) are observed. The above NOE's and participation of NH (2), NH (3), NH (4) and NH (5) in hydrogen bonding confirms the presence of intertwined 12/10/12/10 helix for 41. For 42 along with the above mentioned NOE's seen in 4,5 and 6 also strong intensity NOE's C H(5) / NH (7) and C^ (3) / C_ΩH (p_ro-S) (7) and weak intensity NH (6) / NH (7) are observed. The above NOE's and participation of NH (2), NH (3), NH (4), NH (5), NH (6), NH (7) in hydrogen bonding confirms the presence of intertwined 12/10/12/10/12/10 helix for 42. Leaving apart the first residue the sugar ring orientation with respect to the backbone also seems to be reasonably well defined. The JcpH-c4H of about 10 Hz and the additional presence of NH / H4 and NH / C H(proR) NOE's is in conformity of χi in the vicinity of 180° for these residues. For the first residue the ³Jcp_H-c_4H is small, being 7.3, 7.2,6.0 and 6.2 Hz for 43, 38, 41 and 42. Averaging due to multiple rotamers may be a plausible cause for this. The χi of about 180° makes the sugar rings plane alternately pointing in opposite direction. Thus for 41 the methoxy group at residue 3 and 5 point along the C terminus of the helix axis, where as the ones at 2, 4 and 6 point along the helix axis towards the N terminus. Presence of about 2.7 residues per turn causes sugar rings of every fourth residue to be in each others proximity but slightly displaced by about 40°. In all these molecules the sugar pucker is very well defined. The coupling between protons in the ring are: VCIH-CΏH ~ 3 Hz, ³JC2H-C3H ~ 0 Hz and ³Jc₃H-c4H ~ 4 Hz. These couplings correspond to a ³T₂ sugar pucker. Strong NOE , s.φ_ro-R₎ I iH and Me^s) / C2H as well and weak M&φ_ro-sJ C₄H NOE show that the isopropilidine ring predominantly takes an envelop conformation. The observations are consistence with the structure of such a sugar units in other molecules with C-C glycocidic linkages. The data in DMSO-o^for 43, 38 and 41 was also well understood and almost all the NOE's discussed above were obtained. Though the chemical shift dispersion was not as much as in CDC13 and also some of the couplings indicate little more flexibility in the structure. However, the 12/10/12 helix is very well preserved.

Tetrapeptide-14 and Hexapeptide-17: No characteristic information on a well-defined structure was obtained. In CDC1₃ amide protons appeared below δ < 7 ppm and solvent titration studies did not show their participation in hydrogen bond. In CD₃OD, amide protons exchanged very quickly and most of them could not be detected after 12 hours. The consideration of steric and torsional energies (Wu et al.) does not support regular 14- or 10/12 helix for these oligomers.

Tetrapeptide-32, Hexapeptide-34: In CDC1₃ due to severe overlap in the C_αH and øH region, most of the specific assignments could not be made. Several of the amide resonances appear at low field (δ > 7 .5 ppm) and solvent titration studies indicate that many of the amide protons are participating in hydrogen bonding. Since the amide protons are isolated the 3JNH.β_H coupling could be obtained. The overlap of resonances in other solvents was more severe. In CD₃OD amide proton exchange was fast indicating absence of any structure. The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention. Experimental General: melting points are uncorrected. CH2CI2 was freshly distilled from CaH₂ under N₂. DMF was distilled under reduced pressure from nindrydrin and stored over 4 A molecular sieves. Triethyl amine was distilled from CaH₂ before use. Other solvents and reagents were used as obtained from commercial suppliers. For Boc removal, 10 %THF in CH₂CL2 (checkup) was used. Column chromatography was carried out by using 60 to 120 mesh silica gel. Routine 1H-NMR spectra were obtained on a INONA-500 MHz and 800 MHZ spectrometers and are referenced to residual protonated ΝMR solvents. Routine ¹³C- ΝMR spectra were recorded at 125 MHz and are referenced to the ΝMR solvents. High- resolution electron impact mass spectrometry (or HRMS-FAB) N G Autospec Mass Spectrometer at 5 or 7 K. resolution using perfluoro kerosene as an internal standard. IR spectra were recorded on and reported in wavenumbers (cms^"1). General Procedures (GP) GP-1: Debenzylation of amino ester: Benzyl protected amino acid ester (1.0 mmol) was dissolved in methanol (0.5 mL), treated with 10% Pd-C (0.1 gm for 1.0 g) and stirred at room temperature under hydrogen atmosphere for 12h. After completion of the reaction (TLC analysis), the reaction mixture was filtered and filtrate evaporated. Amine was used as such for further reactions without purification.

GP-2: Boc protection of amino esters: Free amine ester (1.0 mmol) was dissolved in

THF (5 mL) and cooled to 0 °C. (Boc)₂O (1.0 mmol) in THF (5 mL) was added slowly for 15min. The reaction mixture was allowed to warm to room temperature and stirred for 12h. I

THF was evaporated and purified the residue by column chromatography (Silica gel, 15% EtOAc - pet ether) to give pure Boc protected amino acid ester.

GP-3: Hydrolysis of the amino acid ester / peptide ester: A solution of the ester (1.0 mmol) in MeOH (4 mL) was treated with 4Ν NaOH (4 mL) at room temperature. After 2h, methanol was removed and adjusted to pH 2-3 with aq. IN HCl and extracted with EtOAc. The organic layer was dried (Na₂SO₄) and evaporated to give acid. GP-4: Boc deprotection of amino acid / peptide ester: A stirred solution of the amino acid ester or peptide ester (O.lg) in dry CH2CI2 (0.9 mL) was treated at 0 °C under nitrogen atmosphere with CF₃COOH (0.1 mL) at room temperature and stirred for 2h. It was evaporated and the residue dried under high vacuum. The salts were used as such without further purification or characterization. GP-5: Preparation of dipeptides from monomers: Boc amino acid (1.0 mmol) dissolved in dry. CH₂C1₂ (3.5 mL) was sequentially treated with HOBt (1.2 m.mol) and EDCI (1.2 mmol) at 0 °C. After 15 min, free amine ester (1.0 mmol) in dry CH₂C1₂ (2.5 mL) was added to the reaction mixture. The reaction mixture was allowed to reach room temperature and stirred further for lOh. It was diluted with CHC1₃, washed with IN HCl, water, and aq. saturated. NaHCO₃ solution and aq. NaCl solution. The organic layer was dried (Na₂SO₄) and evaporated to give the dipeptides. GP-6: Preparation of tripeptides: Boc protected dipeptide acid (1.0 mmol) dissolved in dry CH₂C1₂ (6 mL) was treated with HOBt (1.2 mmol) and EDCI (1.2 mmol) at 0 °C. After 15 min. amine ester (1.0 mmol; obtained by treatment of amine salt (1.0 mmol) with DIPEA (1.5 mmol)) in dry CH₂C1₂ (2.5 mL) was added. It was allowed to reach room temperature, and stirred for 10 h. The reaction mixture was diluted with CHC1₃, washed with IN HCL water, aq. sat. NaHCO₃ solution and NaCl solution. The organic layer was dried (Na₂SO₄) and evaporated to give tripeptide. GP-7: Preparation of tetra peptides from dipeptides: Dipeptide acid (1.0 mmol) dissolved in dry CH₂C1₂ (6 mL) was treated with HOBt (1.2 mmol) and EDCI (1.2 mmol) at 0 °C and treated with dipeptide amine in dry CH2CI2 (6.5 mL) as described in GP-6 to give tetrapeptide.

GP-8: Preparation of hexa peptides: Tetra peptide acid (1.0 mmol) dissolved in dry

CH₂C1₂: dry DMF (4: 1) (10 mL) was treated with HOBt (1.2 mmol) and EDCI (1.2 mmol) at 0 °C. After 15 min., dipeptide amine (1.0 mmol) in dry CH₂C1₂ (6 mL) was added and worked up as described in GP-6 to give hexapeptides. GP-9: Preparation of octa peptides: Tetrapeptide acid (1.0 mmol) dissolved in dry

CH₂C1₂: dry DMF (4: 1) (10 mL) was treated with HOBt (1.2 mmol) and EDCI (1.2 mmol) at 0 °C. After 15 min. tetra peptide amine (1.0 mmol) in dry CH₂C1₂ (12 mL) was added and work up as described in GP-6 gave octapeptide.

EXAMPLE - 1 Part 1: Unsaturated ester (Scheme 1; 2) Aldehyde 1 (1.95 g, 9.65 mmol) in benzene (10 mL) was added to a stirred solution of (methoxy carbonyl methylene) triphenylphosphine (4.84 g, 14.48 mmol) in benzene

(lOmL) at reflux and stirring was continued for 5h at same temperature. After reaction benzene was removed and crude directly loaded on a flash chromatography column with 10% EtOAc in pet.ether to give 2 (1.71g, 88.7%) as syrup, [α] _D = - 90.8 (c 1.87, CHC1₃), IR (Neat): 2989, 2942, 1725, 1440, 1379, 1260, 1200, 1080, 1020, 875 cm^'1; 'II- MR (500 MHz, CDC1₃) δ 6.96 (dd, J = 4.8,15.8 Hz, IH, T-C₅H), 6.33 (dd, J = 6.9,11.7 Hz, IH, C- C₅H), 6.18 (dd, J= 1.7,15.8 Hz, IH, T-C₆H), 5.97 (d, J= 3.8 Hz, IH, C-CiH), 5.96 (d, J = 3.8 Hz, IH, T-CiH), 5.95 (dd, J = 1.7, 11.7 Hz, IH, C-C₆H), 5.64 (ddd, J= 1.7, 3.2, 6.9 Hz, IH, C-OjH), 4.80 (ddd, J= 1.7, 3.2, 4.8 Hz, IH, T-Gfl), 4.62 (d, J= 3.8 Hz, IH, T- C₂H), 4.61 (d, J = 3.8 Hz, IH, C-C₂H), 4.05 (d, J = 3.2 Hz, IH, C-C₃H),3.78 (d, J = 3.2 Hz, IH, T-C₃H), 3.74 (s, 3H, T-COOMe), 3.74 (s, 3H, C-COOMe), 3.38 (s, 3H, T-OMe), 3.35 (s, 3H, C-OMe), 1.53 (s, 3H, C-Me), 1.51 (s, 3H, T-Me), 1.34 (s, 6H, C&T-Me). Method A To a stirred solution of 2 (0.86 g, 3.33 mmol) in THF benzylamine (0.36 mL, 3.33 mmol) and DBU (0.50 mL, 3.33 mmol) were added and stirred at room temperature for 8h.THF was removed and reaction mixture was directly loaded on chromatography column with 15% EtOAc in pet.ether to give 3 (0.72 g, 59.21%) as a syrup. Method B A stirred solution of 2 (4.0 g, 15.5 mmol) and benzylamine (4.22 mL, 38.76 mmol) was stirred at room temperature. After 12h the reaction mixture was directly loaded on a chromatography column with 10% EtOAc in pet.ether to give 4 (1.25g, 22.1%) as a syrup and 15% EtOAc in pet. ether to give 3 (2.6g, 45.9%) as a syrup. Part 2: Benzyl protected (S) amino acid ester (Scheme 1; 3) [α] _D = - 31.078 (c 1.0, CHC1₃), IR (Neat): 3370, 2980, 2918, 1718, 1449, 1368, 1158, 1072, 1013 cm^'1; 1H-NMR (500 MHz, CDC1₃) δ 7.32 (m, 2H, Ar-H), 7.29 (m, 2H, Ar-H), 7.22 (m, IH, Ar-H), 5.91 (d, J = 3.8 Hz, IH, CH), 4.59 (d, J = 3.9 Hz, IH, C₂H), 4.23 (dd, J= 3.2, 8.7 Hz, IH, QH), 3.86 (abq, J= 12.9 Hz, 2H, Ar-CH₂), 3.73 (d, J= 3.2 Hz, IH, C₃H), 3.69 (s, 3H, -COOMe), 3.41 (dt, J=5.6, 8.7 Hz, IH, C_PH), 3.37 (s, 3H, - OMe), 2.57 (dd, J = 5.6, 14.9 Hz, IH, C_αH'), 2.46 (dd, J- 5.6, 14.9 Hz, IH, C_αH), 1.48 (s, 3H, Me), 1.32 (s, 3H, Me). FAB MS: 366 (M⁺+ H) Part 2: Benzylprotected (R) amino acid ester (Scheme 1; 4) [α] D = - 35.148 (c 1.0, CHC1₃), IR (Neat): 3340, 2983, 2935, 1729, 1455, 1381, 1162, 1074, 1017 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 7.32 (m, 2H, Ar-H), 7.29 (m, 2H,

Ar-H), 7.22 (m, IH, Ar-H), 5.87 (d, J= 3.8 Hz, IH, CtH), 4.57 (d, J = 3.9 Hz, IH, C₂H),

4.12 (dd, J= 3.0, 8.9 Hz, Hi QH), 3.83 (abq, J=14 Hz, 2H, Ar-CH₂), 3.83 (d, J=3.0 Hz,

IH, C₃H), 3.66 (s, 3H, -COOMe), 3.44 (ddd, J= 4.2, 7.2, 8.9 Hz, IH, CpH), 3.39 (s, 3H, - OMe), 2.80 (dd, J= 4.2, 15.6 Hz, IH, C_αFf), 2.57 (dd, J= 7.2, 15.6 Hz, IH, C_αH), 1.48 (s, 3H, Me), 1.32 (s, 3H, Me). FAB MS: 366 (lv + H) Part 3: Debenzylation of (S) amino acid ester (Scheme 2; 5) Debenzylation of 3 (0.82 g, 2.24 mmol) with 10% Pd-C (0.082 g) in methanol (2.5 mL) was performed according to GP-1 to obtain amine 5, which was used as such for further reaction without purification. Part 4: Debenzylation and Boc protection of (S) amino acid ester (Scheme 2; 5a) Debenzylation of 3 (0.82 g, 2.24 mmol) was performed according to GP-1 to obtain amine 5, which was treated with Boc₂O (0.48 mL, 2.07 mmol) as per GP-2 and purified by column chromatography (60-120 mesh Silica-gel, 15% EtOAc-pet. ether) to give 5a (0.61 mg, 72%), [α] _D = - 26.91 (c 1.1, CHC1₃), IR (Neat): 3385, 2980, 2938, 1725, 1705, 1502, 1308, 1161, 1071, 1013 cm^'1; 1H-NMR (500 MHz, CDC1₃) δ 5.91 (d, J= 3.8 Hz, IH, CiH), 5.09 (bs, IH, S-NH), 4.57 (d, J = 3.8 Hz, IH, C₂H), 4.30 (m, IH, C_PH), 4.298 (m, IH, CH), 3.68 (d, J= 3.1 Hz, IH, C₃H), 3.68 (s, 3H, -COOMe), 3.373 (s, 3H, -OMe), 2.71 (dd, J= 3.2, 14,6 Hz, IH, C_αH 2.67 (dd, J= 7.9, 14.6 Hz, IH, C_αH), 1.48 (s, 3H, Me), 1.43 (s, 9H, -Boc), 1.31 (s, 3H, Me). FAB MS: 376 (M⁺+ H) Part 5: Ester hydrolysis of (S) amino acid ester (Scheme 2; 6) Ester 5a (0.60 g, 1.60 mmol) on hydrolysis with 4N NaOH (6.5 mL) in methanol (6.5 mL) was performed according to GP-3 to give 6 (0.49 g, 85%) as a syrup, [α] D = - 43.46 (c 1.0, CHC1₃), IR (Neat): 3353, 2980, 2925, 1710, 1504, 1313, 1161, 1067, 1012 cm^" 1H-NMR (500 MHz, DMSO- 6) δ 6.68 (d, J= 8.0 Hz, IH, S-NH), 5.76 (d, J = 3.8 Hz, IH, CiH), 4.64 (d, J= 3.8 Hz, IH, C₂H), 4.02 (m, IH, C_PH), 4.02 (m, IH, C₄H), 3.58 (d, J = 3.1 Hz, IH, C₃H), 3.29 (s, 3H, OMe), 2.29 (dd, J- 3.2, 14.6 Hz, IH, C_αH'), 2.23 (dd, J= 7.9,14.6 Hz, IH, C_αH), 1.37 (s, 3H, Me), 1.34 (s, 9H, -Boc), 1.23 (s, 3H, Me). FAB MS: 384 (M⁺ + Na)

Part 6: Boc deprotection of (S) amino acid ester (Scheme 2; 7) Boc deprotection of 5a (0.207 g, 0.554 mmol) with TFA (0.20 mL) in CH₂C1₂ (2.0 mL) was performed according to GP-4 to obtain amine salt 7, which was used as such for further reactions without purification. Part 7: Debenzylation of (R) amino acid ester (Scheme 2; 8) Debenzylation of 4 (1.330 g, 3.64 mmol) with 10% Pd-C (0.130 g) in methanol (3.5 mL) was performed according to GP-1 to obtain amine 8, which was used as such for further reactions without purification. Part 8: Debenzylation and Boc protection of (R) amino acid ester (Scheme 2; 8a) Debenzylation of 4 (1.330 g, .54 mmol) was performed according to GP-1 to obtain amine 8, which on treatment with Boc₂O (0.835 mL, 3.64 mmol) as per GP-2 and purification by column chromatography (60-120 mesh Silica-gel, 15% EtOAc-pet. ether) to give 8a (0.98 g, 72%), [α] _D = - 25.616 (c 0.48, CHC1₃), ER. (Neat): 3374, 2979, 2923, 1718, 1499, 1361, 1170, 1080, 1016 cm^'1; 1H-NMR (500 MHz, CDC1₃) δ 5.87 (d, J= 3.9 Hz, IH, CiH), 5.28 (d, J= 6.9 Hz, IH, R-NH), 4.54 (d, J= 3.9 Hz, IH, C₂H), 4.36 (dddd, J= 7.7, 6.9, 6.1, 5.0 Hz, IH, CpH), 4.28 (dd, J = 7.7,3.4 Hz, IH, C₄H), 3.71 (d, J = 3.4 Hz, IH, C₃H), 3.68 (s, 3H, COOMe), 3.40 (s, 3H, OMe), 2.71 (dd, J= 6.1 15.6 Hz, IH, C_αH'), 2.66 (dd, J= 5.0,15.6 Hz, IH, CαH), 1.47 (s, 3H, Me), 1.43 (s, 9H, -Boc), 1.31 (s, 3H, Me). FAB MS: 376 (M⁺+ H) Part 9: Ester hydrolysis of (R) amino acid ester (Scheme 2; 9) Hydrolysis of ester 8a (0.980 g, 2.61 mmol) with 4N NaOH (10.5 mL) in methanol (10.5 mL) was performed according to GP-3 to give 9 (0.815 g, 84%) as a white solid, M. p. 124 - 127 ^C; tot] r> = ~ 22.540 (c 0.55, CHCI3), IR (KBr): 3324, 2983, 2929, 1708, 1643, 1410, 1262, 1160, 1076, 1018- cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 5.88 (d, J = 3.8 Hz, IH, CiH), 5.33 (d, J= 9.4 Hz, IH, R-NH), 4.55 (d, = 3.8 Hz, IH, C₂H), 4.37 (dddd, J = 9.4, 7.6, 5.6, 4.9 Hz, IH, CpH), 4.32 (dd, J= 7.6, 2.6 Hz, IH, C4H), 3.73 (d, J= 2.6 Hz, IH, C₃H), 3.41 (s, 3H, OMe), 2.77 (dd, J= 5.6, 16.2 Hz, IH, CαH), 2.72 (dd, J= 4.9,162 Hz, IH, C_αH'), 1.48 (s, 3H, Me), 1.44 (s, 9H, -Boc), 1.32 (s, 3H, Me). FAB MS: 362 (M⁺ +

H).

Part 10: Boc deprotection of (R) amino acid ester (Scheme 2; 10) Boc deprotection of 8a (0.275 g, 0.73 mmol) with TFA (0.28 mL) in CH₂C1₂ (2.5 mL) was performed according to GP-4 to obtain salt 10. EXAMPLE -2

Part 1: Preparation of dipeptide (Scheme 3; 11) Acid 6 (0.426 g, 1.18 mmol) was treated with HOBt (0.19 g, 1.45 mmol), EDCI (0.27 g, 1.45 mmol) and 5 (prepared by debenzylation of 3 (0.432 g 1.18 mmol) with 10% Pd-C (43 mg) according to GP-1) according to GP-5 and purified by column chromatography (60-120 mesh Silica-gel, 50% EtOAc-pet ether) to give 11 (0.545 g, 75%) as a white solid, M. p. 75 - 78 °C; [α] _D = - 48.21 (c 0.5, CHCI3), IR (KBr): 3365, 2985, 2941, 1741, 1686, 1520, 1365, 1164, 1075, 1012 cm^"1; 1H-NMR (500 MHz, CDCI3) δ 6.36 (d, J= 8.2 Hz, IH, S₂-NH), 5.99 (d, J= 3.9 Hz, IH, dH), 5.91 (d, J = 3.9 Hz, IH, C,H), 5.60 (d, 7= 8.1 Hz, IH, Si-NH), 4.60 (m, IH, CpH), 4.59 (d, J=3.9 Hz, IH, C₂H), 4.58 (d, J= 3.9Hz, IH, C₂H), 4.35 (m, IH, dH), 4.21 (m, IH, CpH), 4.21 ( , IH, dH), 3.82 (d, J = 3.3 Hz, IH, C₃H), 3.75 (d, J = 3.3 Hz, IH, C₃H), 3.68 (s, 3H, -COOMe), 3.41 (s, 3H, - OMe), 3.38 (s, 3H, OMe), 2.68 (dd, IH, J= 7.3, 15.6 Hz, CαH'), 2.61 (dd, 7=5.3, 15.6 Hz, IH, C„H), 2.44 (dd, 7=4.7, 14.1 Hz, IH, CαH'), 2.36 (dd, 7= 4.1, 14.1 Hz, C_αH), 1.48 (s, 3H, Me), 1.46 (s, 3H, Me), 1.44 (s, 9H, -Boc), 1.32 (s, 3H, Me), 1.30 (s, 3H, Me). FAB MS: 619.2 (N^+ H) Part 2: Boc deprotectin of dipetide (Scheme 3; 12) Boc deprotection of 11 (0.67 g, 1.08 mmol) with TFA (0.7 mL) in CH₂C1₂ (7 mL) was performed according to GP-4 to give the amine salt 12. Part 3: Ester-hydrolysis of dipeptide (Scheme 3; 13) Hydrolysis of ester 11 (0.40 g, 0.65 mmol) with 4N NaOH (2.5 mL) in methanol (2.5 mL) was performed according to GP-3 to give 13 (0.365 g, 94%) as a solid, M. p. 64- 66 °C; [α] _D = - 54.22 (c 0.7, CHCfe), IR (KBr): 3365, 2986, 2940, 1723, 1678, 1519, 1368, 1166, 1074, 1015 cm^"1; 1H-NMR (500 MHz, OMSO-d6) δ 7.79 (d, 7= 8.7 Hz, IH, S₂-NH), 6.26 (d, J= 8.1 Hz, IH, S,-NH), 5.78 (d, 7= 3.9 Hz, IH, dH), 5.75 (d, 7= 3.9 Hz, IH, dH), 4.63 (d, 7= 3.9 Hz, IH, C₂H), 4.61 (d, J= 3.9 Hz, IH, C₂H), 4.3 (m, IH, CpH), 4.19 (m, IH, C₄H), 4.04 ( , IH, dH), 3.96 (m, IH, CpH), 3.63 (d, 7 = 3.3 Hz, IH, C₃H), 3.59 (d, 7= 3.3 Hz, IH, C₃H), 3.30 (s, 3H, OMe), 3.29 (s, 3H, OMe), 2.34 (m, 2H, C_αH',H), 2.21(m, 2H, C_αH',H), 1.48 (s, 3H, Me), 1.46 (s, 3H, Me), 1.44 (s, 9H, -Boc), 1.32 (s, 3H, Me), 1.30 (s, 3H, Me). FAB MS: 605 (M⁺+ H) Part 4: Preparation of tetrapeptide (Scheme 3; 14)

Acid 12 (0.655 g, 1.08 mmol) was treated with HOBt (0.176 g, 1.30 mmol), EDCI (0.25 g, 1.30 mmol), 13 (prepared by Boc deprotection of 11 (0.67 g, 1.08 mmol) with TFA (0.7 mL) in CH₂C1₂ (7 mL) according to GP-4) and DIPEA (0.45 mL, 1.63 mmol) according to GP-7 and purified by column chromatography (60-120 mesh Silica-gel, 2.0% Methanol- CHC1₃) to give 14 (0.9 g, 75%) as a white solid, M. p. 124 -126 °C; [α] _D = - 36.79 (c 0.25, CHCI₃), IR (KBr): 3372, 3392.5, 2982, 2933, 1671, 1530, 1369.5, 1169, 1070, 1012 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 6.81 (d, J= 7.9 Hz, IH, S -NH), 6.79 (d, 7 = 7.9 Hz, IH, S₃-NH), 6.57 (d, 7= 7.9 Hz, IH, S₂-NH), 5.92 (d, J = 3.9 Hz, IH, CiH), 5.895 (d, 7 = 3.9 Hz, IH, CiH), 5.89 (d, 7= 3.9 Hz, IH, dH), 5.88 (d, 7= 3.9 Hz, IH, dH), 5.58 (d, 7 = 6.1 Hz, IH, Si-NH), 4.59 (m, IH, CpH), 4.57 (d, 7= 3.9 Hz, IH, C₂H), 4.57 (d, 7= 3.9 Hz, IH, C₂H), 4.56 (d, 7= 3.9 Hz,lH, C₂H), 4.56 (d, 7= 3.9 Hz, IH, C₂H), 4.59 (m, IH, C_βH), 4.53 (m, IH, CpH), 4.36 (m, IH, dH), 4.32 (m, IH, dH), 4.29 (m, IH, QH), 4.25 (m, IH, CpH), 4.25 (m, IH, dH), 3.86 (d, 7= 3.1 Hz, IH, C₃H), 3.80 (d, 7= 2.9 Hz, IH, C₃H), 3.78 (d, 7= 3.0 Hz, IH, C₃H), 3.68 (s, 3H, -COOMe), 3.67 (d, 7= 3.1 Hz, IH, C₃H), 3.40 (s, 3H, OMe), 3.39 (s, 3H, OMe), 3.38 (s, 3H, OMe), 3.37 (s, 3H, OMe), 2.67 (dd, 7 = 5.8, 15.6 Hz, IH, C_αH' 2.59 (dd, 7 = 5.8,15.6 Hz, IH, C_αH), 2.46 (m, 2H, C_αH,H'), 2.43 (m, 2H, C_αH,H'), 2.42 (m, 2H, C_αH,H'), 1.47 (s, 3H, Me), 1.465 (s, 3H, Me),1.46 (s, 6H, 2-Me), 1.43 (s, 9H, -Boc), 1.31 (s, 3H, Me), 1.302 (s, 3H, Me), 1.30 (s, 6H, 2-Me). FAB MS: 1105.1 (M⁺+ H) Part 5: Ester hydrolysis of tetrapeptide (Scheme 3; 15) Hydrolysis of ester 14 (0.6 g, 0.54 mmol) with 4N NaOH (2 mL) in methanol (2 mL) was performed according to GP-3 to give 15 (0.42 g, 71%) as a solid, M. p. 141-143 °C; [α] _D = - 45.72 (c 0.6, CHC1₃), IR (KBr): 3397, 2986, 2937.5, 1656, 1527, 1378, 1167, 1080, 1021 cm^"1; 1H-NMR (500 MHz, DMSO-d6) δ 7.88 (d, 7= 7.9 Hz, IH, S₄-NH), 7.55 (d, 7= 1.9 Hz, IH, S₃-NH), 7.44 (d, 7 = 7.9 Hz, IH, S₂-NH), 6.25 (d, 7 = 6.1 Hz, IH, S,- NH), 5.77 (d, 7= 3.9 Hz, IH, CiH), 5.76 (d, 7=3.9 Hz, IH, CiH), 5.75 (d, 7= 3.9 Hz, IH, CiH), 5.75 (d, 7= 3.9 Hz, IH, CrH), 4.65 (d, 7= 3.9 Hz, IH, C₂H), 4.62 (d, 7= 3.9 Hz, IH, C₂H), 4.61 (d, 7= 3.9 Hz, IH, C₂H), 4.60 (d, 7= 3.9 Hz, IH, C₂H), 4.32 (m, IH, CpH), 4.31 (m, IH, C_βH), 4.29 ( , IH, CpH), 4.21 (m, IH, dH), 4.16 (m, IH, dH), 4.12 (m, IH,

C₄H), 4.06 (m, IH, dH), 3.98 (m, IH, C_βH),3.69 (d, 7= 3.1 Hz, IH, C₃H), 3.67 (d, 7= 2.9 Hz, IH, C₃H), 3.63 (d, 7-3.0 Hz, IH, C₃H), 3.62 (s,lH, C₃H), 3.30 (s, 6H₅ OMe), 3.294 (s,

3H, OMe), 3.29 (s, 3H, OMe), 2.35 (m,lH, C_αH' ), 2.29 (m,lH, C«H), 2.25(m, 2H,

C_αH,H'), 2.26 (m, IH, C_αH'), 2.23 (m, IH, C_αH), 2.20 (m, IH, C_αH'), 2.17 (m, IH, C_αH), 1.38 (s, 3H, Me), 1.37 (s, 3H, Me), 1.36 (s, 3H Me), 1.35 (s, 9H, -Boc), 1.35 (s, 3H, Me), 1.24 (s, 3H, Me), 1.232 (s, 3H, Me), 1.224 (s_: 6H, 2-Me). FAB MS: 11 13.2 (M⁺+ Na) Part 6: Boc deprotectin of tetrapetide (Scheme 3; 16) Boc deprotection of 14 (0.101 g, 0.092 mmol) with TFA (0.1 mL) in CH₂C1₂ (1.0 mL) according to GP-4 gave 16. Part 7: Preparation of hexapeptide (Scheme 3; 17) Acid 15 (0.15 g, 0.138 mmol) was treated with HOBt (0 023 g, 0.165 mmol), EDCI (0.032 g, 0.165 mmol), 12 (prepared by Boc deprotection of 14 (0.085 g, 0.138 mmol) with

TFA (0.1 mL) in CH₂C1₂ (1 mL) as described in GP-4) and DIPEA (0.04 mL, 0.207) according to GP-8 and purified by column chromatography (60-120 mesh Silica gel, 2.5%

Methanol-CHCl₃) to give 17 (0.122 g, 56%) as a white solid, M. p. 140 -142 °C; [ ] _D = - 30.46 (c 0.6, CHCI₃), IR (KBr): 3377, 2987.5, 2938, 1664, 1528, 1376, 1217, 1166, 1080, 1022 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 6.92 (d, 7= 7.9 Hz, IH, S₅-NH), 6.86 (d, 7= 7.9 Hz, IH, S₆-NH), 6.85 (d, 7= 7.9 Hz, IH, S₄-NH), 6.71 (d, 7= 7.9 Hz, IH, S₃-NH), 6.58(d, 7= 7.9 Hz, IH, S₂-NH), 5.92 (d, 7= 3.9 Hz, IH, CiH), 5.895 (d, 7= 3.9 Hz,lH, CiH), 5.89 (d, 7= 3.9 Hz, IH, dH), 5.89 (d, 7= 3.9 Hz, IH, CiH), 5.88 (d, 7= 3.9 Hz, IH, CiH), 5.64 (d, 7= 6.1 Hz, lH, Si-NH), 4.59 (m, IH, CpH), 4.55 (m, IH, CpH), 4.57 (d, 7= 3.9 Hz, IH, C₂H), 4.57 (d, 7= 3.9 Hz, IH, C₂H), 4.56 (d, 7= 3.9 Hz,lH, C₂H), 4.56 (d, 7= 3.9 Hz, lH, C₂H), 4.54 (m, lH, CpH), 4.53 (m, IH, CpH), 4.50 (m,lH, CpH), 4.38 (m, IH, dH), 4.33 (m, IH, dH), 4.32 (m, IH, C^H), 4.31 (m, IH, dH), 4.30 (m, IH, dH), 4.25 (m, IH, CpH), 4.25 (m, IH, dH). 3.86 (d, 7= 3.1 Hz, IH, C₃H), 3.82 (d, J= 2.9 Hz, IH, C₃H), 3.79 (d, 7= 2.9 , 2H, 2-C₃H), 3.77 (d, 7= 3.0 Hz, IH, C₃H), 3.68 (s, 3H, -COOMe), 3.67 (d, 7 = 3.1, IH, C₃H), 3.40 (s, 6H, 2-OMe), 3.39 (s, 3H, OMe), 3.38 (s, 6H, 2-OMe), 3.37 (s, 3H, OMe), 2.67 (dd, 7 = 5.8, 15.6 Hz, IH, C_αH' ), 2.59 (dd, 7 = 5.8, 15.6 Hz, IH, C_«H), 2.46 (m, 2H, Cc LH'), 2.43 (m, 2H, C_αH,H'), 2.42 {m, 2H, C_αH,H'), 1.474 (s, 3H, Me), 1.465 (s, 3H, Me),1.46 (s, 3H, Me), L43 (s, 9H, -Boc), 1.31 (s, 3H, Me), 1.302 (s, 3H, Me), 1.30 (s, 3H, Me). FAB MS: 1592.6 (M⁺+ H) Part 8: Preparation of octapeptide (Scheme 3; 18) Acid 15 (0.10 g, 0.092 mmol) was treated with HOBt (0.015 g, 0.11 mmol), EDCI (0.02 g, 0.11 mmol), 16 {prepared by Boc deprotection of 14 (0.101 g, 0.092 mmol) with TFA (0.1 mL) in CH₂C1₂ (1.0 mL) according to GP-4) and DIPEA (0.024 mL, 0.14) according to GP-9 and purified by column chromatography (60-120 mesh Silica-gel, 3.0% Methanol-CHCl₃) to give 18 (0.075 g, 39%) as a white solid, M. p. 156 -159 °C; [α] _D 25.58 (c 0.45, CHC1₃), IR (KBr): 3378, 2992, 2932, 1667, 1564, 1370, 1156, 1068, 1011 cm^"1; FAB MS: 2078.2 (M⁺+ H) Part 9: Preparation of tripeptide (Scheme 3; 19) Acid 13 (0.335 g, 0.554 mmol) was treated with HOBt (0.090 g, 0.665 mmol), EDCI (0.127 g, 0.665mmol), 7 (prepared by Boc deprotection of 5a (0.208 g, 0.554 mmol) with TFA (0.2 mL) in CH₂C1₂ (2.0 mL) according to GP-4) and DIPEA (0.15 mL, 0.831 mmol) according to GP-6 and purified by column chromatography (60-120 mesh Silica-gel, 75% EtOAc-pet. ether) to give 19 (0.380 g, 80%) as a white solid, M. p. 95 -98 °C; [ ] _D = - 39.52 (c 0.5, CHC1₃), IR (KBr): 3397, 2994, 2935, 1740, 1677, 1521, 1371, 1161, 1074, 1014 cm^"1; 1H-NMR (500 MHz, CDC13) δ 6.56 (d, 7= 8.1 Hz, IH, S₂-NH), 6.56 (d, 7= 8.1 Hz, IH, S₃-NH), 5.92 (d, 7= 3.9 Hz, IH, CiH), 5.91 (d, 7= 3.9 Hz, IH, CiH), 5.91 (d, J= 3.9 Hz, IH, dH), 5.58 (d, 7= 8.1 Hz, IH, S,-NH), 4.60 (m, IH, CpH), 4.57 (d, J= 3.9 Hz, IH, C₂H), 4.56 (d, 7= 3.9 Hz, IH, C₂H), 4.55 (d, 7=3.9 Hz, IH, C₂H), 4.55 (m, IH, CpH), 4.37 (m, IH, dH), 4.35 (m, IH, dH), 4.25 (m, IH, CpH), 4.25 (m, IH, dH), 3.85 (d, J = 3.3 Hz, IH, C₃H), 3.79 (d, 7= 3.3 Hz, IH, C₃H), 3.75 (d, 7= 3.3 Hz, IH, C₃H), 3.68 (s, 3H, -COOMe), 3.40 (s, 3H, OMe), 3.39 (s, 3H, OMe), 3.38 (s, 3H, OMe), 2.67 (m, IH, C_αH'),

\ 2.58 (m, IH, C_αH), 2.46 (m, IH, CαH , 2.41 (m, IH, C_αH',H), 2.38 (m,lH, C_αH),1.49 (s, 3H, Me), 1.47 (s, 3H, Me), 1.47 (s, 3H, Me), 1.43 (s, 9H, -Boc), 1.32 (s, 3H, Me), 1.30 (s, 3H, 2-Me). FAB MS: 884 (M* + Na) EXAMPLE -3 Part 1 : Preparation of dipeptide (Scheme 4; 20) Acid 6 (1.2 g, 3.32 mmol) was treated with HOBt (0.54 g, 4 mmol), EDCI (0.765 g, 4 mmol) and 8 (prepared by debenzylation of 4 (1.21 g 3.32 mmol) with 10% Pd-C (0.12 g) according to GP-1) according to GP-5 and purified by column chromatography (60-120 mesh Silica-geL 50% EtOAc-pet ether) to give 20 (1.55 g, 76%) as a white solid, M p. 73 - 76 °C; [α] _D = -37.414 (c 0.46, CHC1₃), IR (KBr): 3391, 2975, 2934, 1740, 1690, 1648, 1528, 1372, 1170, 1074, 1015 cm^"1; 1H-NMR(500 MHz, CDC1₃) δ 6.70 (d, 7= 8.9 Hz, IH, R₂-NH), 5.92 (d, 7 = 3.8 Hz, IH, dH), 5.89 (d, 7= 3.8 Hz, IH, dH), 5.23 (d, 7= 7.5 Hz, IH, Si-NH), 4.7 (dddd, J= 8.9, 7.7, 6.3, 5.3 Hz, IH, CpH), 4.57 (d, 7= 3.8 Hz, IH, C₂H), 4.54 (d, 7= 3.S Hz, IH, C₂H), 4.31 (dd, 7= 7.7, 3.2 Hz, IH, dH), 4.29 (dd, 7= 6.5, 3.2 Hz, IH, C₄H), 4.16 (dddd, 7= 7.5, 6.5, 5.6, 5.4 Hz, IH, CpH), 3.75 (d, 7= 3.2 Hz, IH, C₃H), 3.73 (d, 7 = 3.2 Hz, IH, C₃H), 3.68 (s, 3H, COOMe), 3.41 (s, 3H, OMe), 3.37 (s, 3H, OMe), 2.69 (dd, J= 6.3, 15.9 Hz, IH, C_αH'), 2.62 (dd, 7= 5.3,15.9 Hz, IH, C_αH), 2.52 (dd, 7 = 5.4, 14.9 Hz, C_αH), 2.41 (dd, 7 = 5.6, 14.9 Hz, C_«H), 1.48 (s, 3H, Me), 1.47 (s, 3H, Me), 1.43 (s, 9H, -Boc), 1.314 (s, 3H, Me), 1.31 (s, 3H, Me). FAB MS: 619.3 (M⁺+ H) Part 2: Boc deprotectin of dipetide (Scheme 4; 21) Boc deprotection of 20 (0.42 g, 0.68 mmol) with TFA (0.4 mL) in CH₂C1₂ (4 mL) was performed according to GP-4 to give the amine salt 21. Part 3: Ester hydrolysis of dipeptide (Scheme 4; 22) Hydrolysis of ester 20 (1.05 g, 1.7 mmol) with 4N NaOH (6.7 mL) in methanol (6.7 mL) was performed according to GP-3 to give 22 (0.86 g, 84%) as a solid, M. p. 107-109 °C; [α] _D = -38.709 (c 0.41, CHC1₃), IR (KBr): 3374, 2980, 2939.5, 1705, 1662, 1529, 1370.5, 1161, 1079, 1011 cm^'1; 1H-NMR (500 MHz, CDC1₃) δ 7.02 (d, 7= 8.5 Hz, IH, R₂- NH), 5.90 (d, 7= 3.8 Hz, IH, C,H), 5.89 (d, 7= 3.8 Hz, IH, dH), 5.27 (d, 7= 7.7 Hz, IH, S NH), 4.67 (m, IH, CpH), 4.58 (d, 7= 3.8 Hz, IH, C₂H), 4.55 (d, 7= 3.8 Hz, IH, C₂H), 4.34 (dd, 7= 6.6, 3.1 Hz, IH, dH), 4.28 (dd, 7=8.0, 3.1 Hz, IH, dH), 4.16 (dddd, 7= 8.0, 7.7, 6.2, 5.2 Hz, IH, CpH ), 3.78 (d, 7 =3.1 Hz, IH, C₃H), 3.73 (d, 7 =3.1 Hz, IH, C₃H), 3.41(s, 3H, OMe), 3.38 (s, 3H, OMe), 2.71 (m, 2H, C_αHC_αH'), 2.53 (dd, 7= 5.2, 14.9 Hz, IH, CαH'), 2.43 (dd, 7= 6.2, 14.9 Hz, C_αH), 1.48 (s, 3H, Me), 1.47 (s, 3H, Me), 1.43 (s, 9H, -Boc), 1.31 (s, 6H, Me). FAB MS: 605.2 ( *+ H) Part 4: Preparation of tetrapeptide (Scheme 4; 23) Acid 22 (0.41 g, 0.68 mmol) was treated with HOBt (0.11 g, 0.82 mmol), EDCI (0.16 g, 0.82 mmol), 21 (prepared by Boc deprotection of 20 (0.42 g, 0.68 mmol) with TFA (0.4 mL) in CH₂C1₂ (4 mL) according to GP-4) and DIPEA (0.18 mL, 1.02 mmol) according to GP-7 and purified by column chromatography (60-120 mesh Silica-gel, 1.5% Methanol-CHCls) to give 23 (0.57 g, 76%) as a white solid, M. p. 124 -127 °C; [α] _D 15.18 (c 0.3, CHCI₃), IR (KBr): 3366, 3286, 2987, 2936, 1718, 1655, 1541, 1374, 1211, 1166, 1081, 1021 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 8.16 (d, 7 = 8.2 Hz, IH, R₄-NH), 7.06 (d, 7= 9.1 Hz, IH, S₃-NH), 6.76 (d, 7= 10.0 Hz, IH, R₂-NH), 5.91 (d, 7= 8.9 Hz, IH, Si-NH), 5.89 (d, 7= 4.0 Hz, IH, dH), 5.88 (d, 7= 3.7 Hz, IH, CiH), 5.87 (d, J= 3.7 Hz, IH, dH), 5.87 (d, 7= 3.7 Hz, IH, CiH), 4.84 (M, IH, CpH), 4.63 (m, IH, CpH), 4.57 (d, 7 = 4.0 Hz, IH, C₂H), 4.55 <d, 7= 3.7 Hz, IH, C₂H), 4.53 (d, 7= 3.7 Hz, IH, C₂H), 4.51 (d, 7 = 4.0 Hz, IH, C₂H), 4.41 (m, IH, CpH), 4.36 (dd, 7= 3.8, 8.8 Hz, IH, dH), 4.29 (dd, 7 = 3.1, 9.9 Hz, IH, dH), 4.14 (m, IH, CpH), 4.13 (dd, 7= 2.8, 9.4 Hz, IH, dH), 4.11 (dd, 7= 3.4, 6.2 Hz, Hi dH), 4.09 (d, 7= 3.1 Hz, Hi C₃H), 3.80 (d, 7= 2.9 Hz, IH, C₃H), 3.78 (d, 7 = 3.4 Hz, IH, C₃H), 3.73 (d, 7 = 3.4 Hz, IH, C₃H), 3.66 (s, 3H, -COOMe), 3.41 (s, 3H, OMe), 3.37 (s, 3H, OMe), 3.37 (s, 3H, OMe), 3.36 (s, 3H, OMe), 2.83 (dd, 7= 3.2, 12.9 Hz, IH, C_αH), 2.66 (dd, 7= 2.3, 12.7 Hz, IH, C_αH), 2,51 (dd, 7= 9.7, 12.9 Hz, IH, C_αH), 2.44 (dd, 7= 5.3, 13.0 Hz, IH, C_αH), 2.43 (dd, 7 = 4.1, 12.8 Hz, IH, C_αH'), 2.41 (dd, 7 = 5.2, 12.8 Hz, IH, C_αH'), 2.18 (dd, 7= 3.6, 13.0 Hz, IH, C_αH'), 2.13 (dd, 7= 10.9, 12.7 Hz, IH, C_αH), 1.49 (s, 3H, Me), 1.44 (s, 3H, Me), 1.44 (s, 9H, Boc), 1.43 (s, 3H, Me), 1.30 (s, 3H, Me), 1.30 (s, 3H, Me), 1.30 (s, 3H, M.e), 1.29 (s, 3H, Me), 1.26 (s, 3H, Me). FAB MS: 1105.3 (M⁺+ H) Part 5: Ester hydrolysis of tetrapeptide (Scheme 4; 24) Hydrolysis of ester 23 (0.35 g, 0.32 mmol) with 4N NaOH (1.2 mL) in methanol (1.2 mL) was performed according to GP-3 to give 24 (0.30 g, 88%) as a solid, M. p. 139- 142 °C; [α] _D = -33.552 (c 0.4, CHCI3), IR (KBr): 3344, 2988, 2938, 1718.5, 1663, 1527, 1376, 1217, 1166, 1081, 1020 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 7.65 (d, 7= 8.2 Hz, IH, R₄-NH), 7.23 (d, 7= 9.1 Hz, IH, S₃-NH), 6.99 (d, 7= 10.0 Hz, IH, R₂-NH), 5.90 (d, 7= 3.9 Hz, IH, CiH), 5.89 (d, 7= 4.0 Hz, IH, dH), 5.88 (d, 7= 3.7 Hz, Hi dH), 5.87 (d, 7= 3.7 Hz, IH, dH), 5.64 (d, 7= 9.5 Hz, IH, Si-NH), 4.70 (m, IH, CpH), 4.69 (m, IH, CpH), 4.59 (d, 7= 4.0 Hz, IH, C₂H), 4.56 (d, 7= 3.7 Hz, IH, C₂H), 4.55 (d, 7= 3.7 Hz, IH, C₂H), 4.54 (d, 7= 4.0 Hz, IH, C₂H), 4.45 (m, IH, CpH), 4.35 (dd, 7= 3.8, 8.8 Hz, IH, dH), 4.31 (dd, 7= 3.1, 9.9 Hz, IH, dH), 4.29 (dd, 7 = 3.1, 9.9 Hz, IH, dH), 4.26 (dd, 7 = 2.8, 9.4 Hz, IH, dH), 4.17 (m, IH, CpH), 3.97 (d, 7= 3.1 Hz, Hi C₃H), 3.85 (d, 7= 2.9 Hz, IH, C₃H), 3.79 (d, 7= 3.4 Hz, IH, C₃H), 3.75 (d, 7= 3.4 Hz, IH, C₃H), 3.41 (s, 3H, OMe), 3.39 (s, 3H, OMe), 3.38 (s, 3H, OMe), 3.36 (s, 3H, OMe), 2.81 (dd, 7 = 3.2, 12.9 Hz, IH, C_αH), 2.62 (dd, 7= 2.3, 12.7 Hz, Hi C_αH), 2.52 (dd, 7= 9.7, 12.9 Hz, IH, C_αH'), 2.51 (dd, 7 = 5.3, 13.0 Hz, Hi C_αH), 2.48 (dd, 7= 4.1, 12.8 Hz, IH, C_αH), 2.46 (dd, 7= 5.2, 12.8 Hz, Hi C_αH'), 2.36 (dd, 7= 3.6, 13.0 Hz, IH, C_αH'), 2.28 (dd, 7= 3.6, 13.0 Hz, IH, C_αH), 1.49 (s, 3H, Me), 1.486 (s, 3H, Me), 1.48 (s, 3H, Me),1.46 (s, 3H, Me),1.44 (s, 9H, Boc), 1.31 (s, 6H, 2XMe), 1.302 (s, 3H, Me), 1.30 (s, 3H, Me). FAB MS: 1113.2 (M^÷ Na) Part 6: Boc deprotectin of tetrapetide (Scheme 4; 25) Boc deprotection of 24 (0.16 g, 0.14 mmol) with TFA (0.15 mL) in CH₂C1₂ (1.5 mL) according to GP-4 gave 25. Part 7: Preparation of hexapeptide (Scheme.4; 26) Acid 24 (0.1 g, 0.09 mmol) was treated with HOBt (0.015 g, 0.11 mmol), EDCI

(0.022 g, 0.11 mmol), 21 (prepared by Boc deprotection of 20 (0.057 g, 0.09 mmol) with TFA (0.1 mL) in CH₂C1₂ (1 mL) as described in GP-4) and DIPEA (0.03 mL, 0.14 mmol) according to GP-8 and purified by column chromatography (60-120 mesh Silica gel, 2.0% Methanol-CHCl₃) to give 26 (0.085 g, 58%) as a white solid, M. p. 114-116 °C; [α] _D = + 7.59 (c 0.35, CHC1₃), IR (KBr): 3381, 2986, 2934, 1716, 1651, 1557.5, 1374, 1166, 1081, 1022 cm^"1; 1H-NMR (500 MHz, CDCl₃) δ 8.75 (d, 7= 9.6 Hz, IH, R_t-NH), 8.62 (d, 7= 9.6 Hz, IH, R₆-NH) 7.69 (d, 7= 9.9 Hz, IH, S₃-NH), 7.30 (d, 7= 8.7 Hz, IH, S₅-NH), 6.71 (d, 7 = 10.2 Hz, IH, R₂-NH), 6.10 (d, 7 = 7.3 Hz, IH, Si-NH), 5.94 (d, 7 = 3.8 Hz, IH, CiH), 5.89 (d, 7= 3.7 Hz, IH, dH), 5.88 (d, 7= 4.0 Hz, IH, CiH), 5.87 (d, 7= 3.7 Hz, IH, C,H), 5.79 (d, 7= 3.8 Hz, IH, dH), 5.78 (d, 7= 3.8 Hz, IH, CiH), 5.10 (m, IH, CpH), 4.70 (m, IH, CpH), 4.60 (m, IH, CpH), 4.59 (d, 7= 3.7 Hz, IH, C₂H), 4.55 (d, 7= 4.0 Hz, IH, C₂H), 4.53 (d, 7= 3.8 Hz, IH, C₂H), 4.53 (d, 7= 3.7 Hz, IH, C₂H), 4.50 (d, 7= 3.8 Hz, Hi C H), 4.49 (d, 7= 3.8 Hz, IH, C₂H), 4.41 (m, Hi CpH), 4.35 (dd, 7 = 3.2, 10.2 Hz, Hi dH), 4.33 (dd, 7 = 3.2, 10.7 Hz, IH, dH), 4.27 (dd, 7 = 2.9, 9.0 Hz, IH, dH), 4.24 (m, IH, CpH), 4.18 (dd, 7 = 2.8, 10.0 Hz, IH, H), 4.15 (m, IH, CpH), 4.13 (d, 7 = 3.2 Hz, Hi C₃H), 4.13 (dd, 7= 3.2, 4.6 Hz, IH, dH), 4.12 (d, 7= 3.2 Hz, Hi C₃H), 4.07 (dd, 7= 3.0, 9.8 Hz, IH, C_tH), 3.78 (d, 7= 2.9 Hz, IH, C₃H), 3.77 (d, 7= 2.8 Hz, IH, C₃H), 3.70 (d, 7 = 3.2, IH, C₃H), 3.68 (d, 7= 3.0, IH, C₃H), 3.64 (s, 3H, -COOMe), 3.40 (s, 3H, OMe), 3.39 (s, 3H, OMe), 3.38 (s, 3H, OMe), 3.36 (s, 3H, OMe), 3.35 (s, 3H, OMe), 3.32 (s, 3H, OMe), 2.83 (dd, 7= 2.6, 12.9 Hz, IH, C_αH'), 2.77 (dd, 7 = 3.0, 12.4 Hz, IH, C_αH*), 2.76 (dd, 7= 2.0, 12.4 Hz, IH, C_αH'), 2.55 (dd, 7=12.3,12.4 Hz, Hi C_αH), 2.45 (dd, 7 = 5.0, 14.1 Hz, IH, C_αH), 2.43 (dd, 7= *, 13.1 IH, C_αH), 2.42 (dd, 7= 5.0, 12.7 Hz, IH, C_αH), 2.34 (dd, 7= 4.1, 14.1 Hz, IH, C_αH'), 2.28 (dd, 7= 12.3, 12.9 Hz, IH, C_αH), 2.19 (dd, 7= 2.6, 13.1 Hz, Hi C_αH'), 2.07 (dd, 7= 2.8, 12.7 Hz, Hi C_αH'), 2.02 (dd, 7= 12.1, 12.4 Hz, IH, C_αH), 1.47 (s, 3H, Me), 1.45(s, 9H, Boc), 1.45 (s, 3H, Me), 1.45 (s, 3H, Me), 1.45 (s, 3H, Me), 1.43 (s, 3H, Me), 1.43 (s, 3H, Me), 1.37 (s, 3H, Me), 1.29 (s, 3H, Me), 1.28 (s, 3H, Me), 1.28 (s, 3H, Me), ϊ.28 (s, 3H, Me), 1.26 (s, 3H, Me). FAB MS: 1592.6 (M*+ H) Part 8: Preparation of octapeptide (Scheme 4; 27) Acid 24 (0.15 g, 0.14 mmol) was treated with HOBt (0.022 g, 0.17 mmol), EDCI (0.032 g, 0.17 mmol), 25 (prepared by Boc deprotection of 23 (0.16 g, 0.14 mmol) with TFA (0.16 mL) in CH₂C1₂ (L5 mL) according to GP-4) and DIPEA (0.04 mL, 0.20 mmol) according to GP-9 and purified by column chromatography (60-120 mesh Silica-gel, 2.5% Methanol-CHCl₃) to give 27 (0.112 g, 39%) as a white solid, M. p. 166-169 °C; [α] _D = +4.851 (c 0.35, CHC1₃), IR (KBr): 3383, 2986, 2935, 1718, 1649, 1539, 1376.5, 1166, 1081, 1022 cm^"1; 1H-NMR (500 MHz, CDCl₃) δ 9.00 (d, 7= 9.7 Hz, IH, Rg-NH), 8.692 (d, 7= 9.7 Hz, IH, R.-NH), 8.616 (d, 7= 9.7 Hz, IH, Rs-NH), 8.124 (d, 7= 9.1 Hz, IH, S₅- NH), 7.75 (d, 7= 9.7 Hz, IH, S₃-NH), 7.16 (d, 7= 8.7 Hz, IH, S₇-NH), 6.66 (d, 7= 9.7 Hz, IH, R₂-NH), 6.18 (d, 7= 8.7 Hz, IH, Si-NH), 5.94 (d, 7 = 3.8 Hz, IH, CiH), 5.89 (d, 7 = 3.7 Hz, IH, CiH), 5.88 (d, 7= 4.0 Hz, IH, CiH), 5.87 (d, 7= 3.7 Hz, Hi CiH), 5.86 (d, 7 =

3.7 Hz, IH, C,H), 5.85 (d, 7= 3.7 Hz, IH, C,H), 5.81 (d, 7= 3.8 Hz, Hi CiH), 5.79 (d, 7 =

3.8 Hz, IH, CiH), 5.06 (m, IH, CpH), 4.73 (m, IH, CpH), 4.72 (m, IH, CpH), 4.56 (d, 7 = 3.7 Hz, IH, C₂H), 4,55 (m, IH, CpH), 4.55 (d, 7= 3.7 Hz, IH, C₂H), 4.555 (d, 7= 4.0 Hz, IH, C₂H), 4.555 (d, 7= 3.8 Hz, IH, C₂H), 4.52 (d, 7= 3.7 Hz, IH, C₂H), 4.52 (d, 7 = 3.8 Hz, IH, C₂H), 4.51 (d, 7= 3.8 Hz, IH, C₂H), 4.51 (d, 7 = 3.8 Hz, IH, C₂H), 4.39 (m, IH, CpH), 4.35 (dd, 7= 3.2, 10.2 Hz, IH, C₄H), 4.33 (m, IH, CpH), 4.30 (dd, 7= 3.2, 10.7 Hz, IH, dH), 4.32 (dd, 7= 3.0, 9.5 Hz, Hi dH), 4.31 (dd, 7=3.1, 10.5 Hz, IH, dH), 4.27 (m, lHfCpH), 4.17 (d, J=3.1 Hz,lH, C₃H), 4.15 (dd, 7= 2.9 , 10.2 Hz, IH, dH), 4.14 (m, IH, CpH), 4, 14 (dd, 7= 3.0, 9.7Hz, IH, dH), 4.13 (dd, 7= 3.1, 6.5 Hz, IH, dH), 4.17 (d, 7= 3.2 Hz, Hi C₃H), 4.11 (d, 7 = 3.1 Hz, IH, C₃H), 4.10 (d, 7 = 3.1 Hz, IH, C₃H), 4.06 (dd, J=3.1, 11.9 Hz, IH, C₄H), 3.81 (d, 7 = 3.2 Hz, IH, C₃H), 3.723 (d, 7 = 3.0 Hz, IH, C₃H), 3.72 (d, 7= 2.9 Hz, IH, dH), 3.69 (d, 7= 3.1 Hz, IH, C₃H), 3.65 (d, J=3.1Hz, 3H, C₃H), 3.65 (s, 3H, -COOMe), 3.40 (s, 3H, OMe), 3.39 (s, 3H, OMe), 3.37 (s, 3H, OMe), 3.366 (s, 6H, 2-OMe), 3.344 (s, 3H, OMe), 3.34 (s, 3H, OMe), 3.32 (s, 3H, OMe), 2.93(dd, 7 = 2.2, 12.8 Hz, IH, C_αH'), 2.8 (dd, 7= 1.7, 12.8 Hz, IH, C_αH), 2.768 (dd, 7 = 2.7, 12.9 Hz, IH, C_αH'), 2.74 (dd, 7= 2.3, 12.8 Hz, IH, C_αH'), 2.6 (dd, 7= 2.4, 12.9 Hz, IH, C_αH'), 2.49 (dd, 7= 2.4, 12.7 Hz, IH, C_αH'), 2.47 (dd, 7= 2.7, 12.8 Hz, IH, CαH), 2.45 (dd, 7 = 4.3, 13.8 Hz, Hi C_αH), 2.44 (dd, 7= 5.4, 12.8 Hz, IH, C_αH), 2.4 (dd, 7= 5.7, 12.8 Hz, IH, C_αH), 2.33 (dd, 7= 5.3, 13.8 Hz, IH, C_αH'), 2.26 (dd, 7= 2.3, 12.8 Hz, IH, C_αH), 2.18 (dd, 7= 2.3, 12.8 Hz, IH, C_αH), 2.13 (dd, 7= 2.4, 12.8 Hz, IH, C_αH'), 2.08 (dd, 7 = 4.3, 12.7 Hz, IH, C_αH'), 2.01 {dd, 7= 11.7, 12.8 Hz, Hi C_αH), 1.47 (s, 6H, 2-Me), 1.45(s, 9H, Boc), 1.42 (s, 3H, Me), 1.41 (s, 3H, Me), 1.36 (s, 6H, 2-Me), 1.30 (s, 6H, 2-Me), 1.284 (s, 3H, Me), 1.28 (s, 6H, 2-Me), 1.25 (s, 3H, Me), 1.26 (s, 6H, 2-Me). FAB MS: 2078.8 (M⁺ + H) Part 9: Preparation of tripeptide (Scheme 4; 28) Acid 22 (0.4 g, 0.66 mmol) was treated with HOBt (0.107 g, 0.8 mmol), EDCI (0.152 g, 0.8 mmol), 7 (prepared by Boc deprotection of 5a (0.248 g, 0.66 mmol) with

TFA (0.25 mL) in CH₂C1₂ (2.5 mL) according to GP-4) and DIPEA (0.17 mL, 0.99 mmol) according to GP-6 and purified by column chromatography (60-120 mesh Silica-gel, 70%

EtOAc-pet. ether) to give 28 (0.46 g, 81%) as a white solid, M. p. 92-95 °C; [α] _D

41.06 (c 0.4, CHC1₃), IR (KBr): 3396, 2985, 2933, 1725, 1669, 1534, 1380, 1169, 1074.5, 1004 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 7.035 (d, 7= 8.3 Hz, IH, S₃-NH), 7.033 (d, 7 =

8.3 Hz, IH, R₂-NH), 5.91 (d, 7= 3.8 Hz, IH, CiH), 5.90 (d, 7= 3.8 Hz, IH, CiH), 5.89 (d, 7

= 3.8 Hz, IH, CiH), 5.42 (d, 7= 8.2 Hz, IH, Si-NH), 4.64 (m, IH, CpH), 4.55 (d, 7 = 3.8

Hz, IH, C₂H), 4.54 (d, 7= 3.8 Hz, IH, C₂H), 4.53 (m, IH, CpH), 4.51 (d, 7 = 3.8 Hz, IH,

C₂H), 4.43 (dd, 7= 3.2, 7.6 Hz, IH, dJH), 4.28 (dd, 7= 3.2, 7.5 Hz, IH, C₄H), 4.24 (m,lH, CpH), 4.24 (dd, 7= 3.2, 6.8 Hz, IH, dH), 3.75 (d, 7= 3.1 Hz, IH, C₃H), 3.70 (d, 7= 3.3

Hz, IH, C₃H), 3.68 (s, 3H, -COOMe), 3.67 (d, 7 = 3.2 Hz, IH, C₃H), 3.39 (s, 3H, OMe),

3.37 (s, 3H, OMe), 3.36 (s, 3H, OMe), 2.67 (dd, J= 5.1,15.2 Hz, IH, C«H'), 2.63 (dd, J=

6.7,15.2 Hz, IH, C_αH), 2.52 (m, IH, C«H), 2.52 (m, IH, C_αH'), 2.44 (m, IH, C_αH), 2.37 (m, IH, C_αH), 1.49 (s, 3H, Me), 1.47 (s, 6H, 2xMe), 1.43 (s, 9H, -Boc), 1.313 (s, 3H, Me), 1.309 (s, 3H, Me), 1.307 (s, 3H, Me). FAB MS: 884.3 (Ivf+Na) EXAMPLE -4 Part 1: Preparation of dipeptide (Scheme 5; 29) Acid 9 (0.81 g, 2.24 mmol) was treated with HOBt (0.36 g, 2.7 mmol), EDCI (0.52 g, 2.7 mmol) and 8 (prepared by debenzylation of 4 (0.82 g 2.24 mmol) with 10% Pd-C (0.08 g) according to GP-1) according to GP-5 and purified by column chromatography (60-120 mesh Silica-gel, 50% EtOAc-pet ether) to give 29 (1.1 g, 79%) as a white solid, M. p. 74-77 °C; [α] _D = -39.3 (c 0.5, CHC1₃), IR (KBr): 3408, 2994, 2939.5; 1718, 1500, 1370, 1161, 1067, 1011 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 6.69 (d, 7= 8.6 Hz, IH, R₂- NH), 5.88 (d, 7= 3.9 Hz, IH, dH), 5.84 (d, 7= 3.8 Hz, IH, dH), 5.8 (d, 7= 9.4 Hz, IH, Ri-NH), 4.65 (dddd, 7= 8.6, 7.3, 5.9, 5.6 Hz, IH, CpH), 4.54 (d, 7= 3.9 Hz, IH, C₂H), 4.53 (d, 7= 3.9 Hz, IH, C₂H), 4.33 (dd, 7= 3.1,.7.3 Hz, Hi dH), 4.31 (m, Hi CpH), 4.17 (m, IH, dH), 3.73 (d, 7=3.1, IH, C₃H), 3.68 (s, 3H, -COOMe), 3.67 (d, 7=2.8, C₃H), 3.41 (s, 3H, OMe), 3.40 (s, 3H, OMe), 2.75 (dd, 7= 5.9,15.6 Hz, IH, C_αH), 2.61 (dd, 7= 5.6,15.6

Hz, IH, C_αH'), 2.54 (dd, 7= 4.5, 14.8 Hz, C_αH), 2.46 (dd, 7= 4.5, 14.8 Hz, IH, C_αH , 1.47

(s, 3H, Me), 1.46 (s, 3H, Me), 1.43 (s, 9H, -Boc), 1.31 (s, 3H, Me), 1.29 (s, 3H, Me). FAB

MS: 619.3 (M⁺+- H)

Part 2: Boc deprotectin of dipetide (Scheme 5; 30) Boc deprotection of 29 (0.36 g, 0.58 mmol) with TFA (0.3 mL) in CH₂C1₂ (3.5 mL) was performed according to GP-4 to give the amine salt 30. Part 3: Ester hydrolysis of dipeptide (Scheme 5; 31) Hydrolysis of ester 29 (0.5 g, 0.81 mmol) with 4N NaOH (3.2 mL) in methanol (3.2 mL) was performed according to GP-3 to give 31 (0.45 g, 92%) as a solid, M. p: 114-116 °C; [α] _D = -27.822 (c 0.5, CHC1₃); IR (KBr): 3392, 2991, 2939, 1721, 1515, 1383, 1257, 1167, 1063, 1014 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 6.55 (d, 7 = 8.6 Hz, IH, R₂-NH), 5.99 (d, 7 = 9.6 Hz, IH, R_rNH), 5.88 (d, 7 = 3.9 Hz, IH, dH), 5.84 (d, 7 = 3.8 Hz, Hi CiH), 4.77 (dddd, 7 = 8.7, 7.3, 5.9, 5.6 Hz, IH, CpH), 4.54 (d, 7= 3.9 Hz, IH, C₂H), 4.53 (d, 7= 3.9 Hz, IH, C₂H), 4.35 (m, IH, CpH), 4.26 (dd, J = 3.4, 5.8 Hz, IH, dH), 4.16 (m, IH, C₄H), 3.76 (d, 7= 3.1 Hz, IH, C₃H), 3.66 (d, 7= 2.8 Hz, C₃H), 3.41 (s, 3H, OMe), 3.40 (s, 3H, OMe), 2.75 (dd, 7= 5.9,15.6 Hz, IH, C_αH), 2.61 (dd, 7 = 5.6, 15.6 Hz, IH, C_αH 2.54 (dd, 7 = 4.5, 14.8 Hz, C_«H), 2.46 (dd, 7 = 4.5,14.8 Hz, IH, C_αH^f), 1.47 (s, 3H, Me), 1.46 (s, 3H, Me), 1.43 (s, 9H, -Boc), 1.31 (s, 3H, Me), 1.29 (s, 3H, Me). FAB MS: 605.2 (M⁺+ H) Part 4: Preparation of tetrapeptide (Scheme 5; 32) Acid 31 (0.35 g, 0.58 mmol) was treated with HOBt (0.94 g, 0.69 mmol), EDCI (0.13 g, 0.69 mmol), 30 (prepared by Boc deprotection of 29 (0.36 g, 0.58 mmol) with TFA (0.3 mL) in CH₂C1₂ (3.5 mL) according to GP-4) and DIPEA (0.12 mL, 0.87 mmol) according to GP^:7 and purified by column chromatography (60-120 mesh Silica-gel, 2.0% Methanol-CHCl₃) to give 32 (0.47 g, 73.5%) as a white solid, M. p. 195 -197 °C; [α] _D 28.98 (c 0.5, CHC1₃), IR (KBr): 3394, 3352, 2987, 2935, 1724, 1674, 1526, 1373, 1218, . 1166, 1082, 1020 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 7.21 (d, 7 = 7.9 Hz, IH, R₃-NH), 7.11 (d, 7 = 7.9 Hz, IH, R₂-NH), 7.00 (d, 7= 7.9 Hz, IH, R₄-NH), 5.87 (d, 7= 3.9 Hz, IH, CiH), 5.86 (d, 7= 3.9 Hz, IH, CiH), 5.86 (d, 7= 3.9 Hz, IH, dH), 5.85 (d, 7= 3.9 Hz, Hi CiH), 5.82 (d, 7= 6.1 Hz, IH, R NH), 4.53 (d, 7= 3.9 Hz, IH, C₂H), 4.525 (d, 7= 3.9 Hz, IH, C₂H), 4.52 (d, 7=3.9 Hz, Hi C₂H), 4.51 (d, 7= 3.9 Hz, IH, C₂H), 4.61 (m, IH, CpH), 4.51 (m, IH, CpH), 4,49 {m, IH, CpH), 4.34 (m, IH, dH), 4.32 (m, IH, dH), 4.30 <m, Hi CpH), 4.30 (m, IH, dH), 4.25 (m, Hi dH), 3.73 (d, 7= 3.1 Hz, IH, C₃H), 3.71 (d, 7= 2.9 Hz, IH, C₃H), 3.70 (d, 7= 3.0 Hz, IH, C₃H), 3.70 (d, 7= 3.1 Hz, IH, C₃H), 3.68 (s, 3H, - COOMe), 3.4 (s,3H,-OMe), 3.394 (s, 3H, OMe), 3.392 (s, 3H, OMe), 3.388 (s, 3H, OMe), 2.75 (dd, 7= 5.S, 15.6 Hz, Hi C„H'), 2.67 (dd, 7= 4.2, 15.6 Hz, IH, C_αH), 2.57 (m, IH, C_αH'), 2.54 (m, IH, C_«Hj, 2.51 (m, 2H, C_αH,H',), 2.49 (m, IH, J1 2.48 (m, IH, C_αH), 1.462 (s, 6H, 2-Me), 1.46 (s, 3H, Me),1.45 (s, 3H, Me), 1.43 (s, 9H, -Boc), 1.305 (s, 3H, Me), 1.295 (s, 3H, Me), 1.29 (s, 6H, 2-Me). FAB MS: 1105.3 (M⁺ + H). Part 5: Ester hydrolysis of tetrapeptide (Scheme 5; 33) Hydrolysis of ester 32 (0.2 g, 0.18 mmol) with 4N NaOH (0.7 mL) in methanol (0.7 mL) was performed according to GP-3 to give 33 (0.17 g, 86%) as a solid, M. p. 202 -205

°C; [α] D = -27.32 (c 0.51, CHC1₃), IR (KBr): 3348, 3010, 2940, 1678, 1647, 1527, 1380, 1 166, 1075, 1018 cm^"1; 1H-NMR (500 MHz, CDCI₃) δ 7.21 (d, 7 = 7.9 Hz, IH, R₃-NH),

7.11 (d, 7 = 7.9 Hz, IH, R₂-NΗ), 7.00 (d, 7= 7.9 Hz, IH, Rt-NH), 5.92(d, 7= 3.9 Hz, Hi dH), 5.895 (d, 7 = 3.9 Hz, Hi CiH), 5.89 (d, 7= 3.9 Hz, IH, CiH), 5.88 (d, 7 = 3.9 Hz, IH, CiH), 5.82 (d, 7 = 6.1 Hz,lH, Ri-NH), 4.59 (m, IH, CpH), 4.57 (d, 7 = 3.9 Hz, IH,

C₂H), 4.57 (d, 7= 3.9 Hz, IH, C₂H), 4.56 (d, 7= 3.9 Hz,Hi C₂H), 4.56(d, 7= 3.9 Hz, IH,

C₂H), 4.61 (m, IH, CpH), 4.51 (m, IH, CpH), 4.49 (m, IH, CpH), 4.34 (m, Hi dH), 4.32

(m, IH, CiH), 4.30 (m, IH, CpH), 4.30 (m, IH, GOT), 4.25 (m, IH, dH), 3.73 (d, 7= 3.1 Hz, IH, C₃H), 3.71 (d, 7= 2.9 Hz, IH, C₃H), 3.70 (d, 7= 3.0 Hz, IH, C₃H), 3.70 (d, 7= 3.1 Hz, IH, C₃H), 3.394 (s, 3H, OMe), 3.392 (s, 3H, OMe), 3.333 (s, 3H, OMe), 3.34 (s, 3H, OMe), 2.73 (dd, 7 = 5.8, 15.6 Hz, IH, C_αH' ), 2.67 (dd, 7 = 5.8, 15.6 Hz, IH, C_αH), 2.57 (m, IH, C_αH'), 2.54 (m, IH, C_αH , 2.51 (m, 2H, C_αH,H,), 2.49 (m, IH, CαH , 2.48 (m, IH, C_αH), 1.462 (s, 6H, 2-Me), 1.46 (s, 3H, Me),1.45 (s, 3H, Me), 1.43 (s, 9H, -Boc), 1.305 (s, 3H, Me), 1.295 (s, 3H, Me), 1.29 (s, 6H, 2-Me). Part 6: Preparation of hexapeptide (Scheme 5; 34) Acid 33 (0.125 g, 0.115 mmol) was treated with HOBt (0.019 g, 0.14 mmol), EDCI (0.027 g, 0.14 mmol), 30 (prepared by Boc deprotection of 29 (0.071 g, 0.115 mmol) with TFA (0.7 mL) in CH₂C1₂ (1 mL) as described in GP-4) and DIPEA (0.03 mL,.0.17 mmol) according to GP-8 and purified by column chromatography (60-120 mesh Silica gel, 2.5% Methanol-CHCl₃) to give 34 (0.094 g, 51.5%) as a white solid, M. p. 224-227 °C; [α] _D 32.723 (c 0.75, CHC1₃), IR (KBr): 3348, 2988, 2935, 1724, 1651, 1525, 1373, 1217.5, 1166, 1082, 1020 cm^"1; 1H-NMR (500 MHz, CDCI₃) δ 7.56 (d, 7= 8.9 Hz, IH, Rj-NH), 7.54 (d, 7 = 8.9 Hz, Hi R₂-NH), 7.34 (d, 7= 8.9 Hz, IH, R5-NH), 7.18 (d, 7= 9.1 Hz, IH, R₃-NH), 7.08 (d, 7= 9.2 Hz, Hi R₅-NH), 5.92 (d, 7= 3.9 Hz, IH, dH), 5.78 (d, 7 = 3.9 Hz, IH, dH), 5.89 (d, 7= 3.9 Hz, IH, dH), 5.88 (d, 7= 3.9 Hz, Hi CiH), 5.78 (d, 7= 9.3 Hz, IH, Ri-NH), 4.60 (m, IH, CpH), 4.47 (m, IH, CpH), 4.46 (m,lH, CpH), 4.40 (m, IH, CpH), 4.39 (m, IH, CpH), 4.56(d, 7= 3.9 Hz,Hi C₂H), 4.51 (d, 7= 3.9 Hz, Hi C₂H), 4.49 (d, 7= 3.8 Hz, IH, C₂H), 4.34 (m, Hi dH), 4.33 (m, IH, dH), 4.33 (m,lH, CpH), 4.32 (m, IH, dH),4.31(m, IH, dH), 3.75 (d, 7= 3.1 Hz, IH, C₃H), 3.73 (d, 7 = 3.1 Hz, IH, C₃H), 3.69 (m, 3H, 3-H3), 3.68 (s, 3H, -COOMe), 3.70 (d, 7= 3.1 Hz, IH, C₃H), 3.394 (s, 3H, OMe), 3.392 (s, 3H, OMe), 3.388 (s, 3H, OMe), 3.34 (s, 3H, OMe), 2.73 (dd, 7= 5.8, 15.6 Hz, IH, C_αH' ), 2.67 (dd, 7= 5.8,15.6 Hz, Hi C_αH), 2.57 (m, IH, C_αH), 2.54 (m, IH, C«H'), 2.51 (m, 2H, C_αH, H'), 2.49 (m,lH, C_oH. 2.48 (m,lH, C_αH), 1.462 (s, 3H, Me), 1.46 (s, 3H, Me),1.45 (s, 3H, Me), 1.43 (s, 9H, -Boc), 1.305 (s, 3H, Me), 1.295 (s, 3H, Me), 1.29 (s, 6H, 2-Me). FAB MS: 1592.3 (M⁺+ H) EXAMPLE -5

Part 1: Preparation of dipeptide (Scheme 6; 35) Acid 9 (1.65 g, 4.57 mmol) was treated with HOBt (0.74 g, 5.48 mmol), EDCI

(1.05g, 5.48 mmol) and 5 (prepared by debenzylation of 3 (1.67 g 4.57 mmol) with 10% Pd-C (0.16 g) according to GP-1) according to GP-5 and purified by column chromatography (60-120 mesh Silica-gel, 50% EtOAc-pet ether) to give 35 (2.24 g, 79%) as a white solid, M. p. 157 -160 °C; [α] _D = -40.763 (c 0.49,CHC13), IR (KBr): 3335, 3269, 2991, 2938, 1730, 1700, 1650, 1526, 1167, 1074, 1013 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 6.48 (d, 7= 8.3 Hz, IH, S₂-NH), 5.68 (d, 7= 8.7 Hz, IH, R NH), 5.91 (d, 7= 3.9 Hz, IH, CiH), 5.87 (d, 7= 3.9 Hz, IH, CiH), 4.59 (m, IH, CpH), 4.55 (d, 7 = 3.9 Hz, IH, C₂H), 4.53 (d, 7 = 3.9Hz, IH, C₂H), 4.37 (m, IH, dH), 4.26 ( , IH, CpH), 4.25 (m, IH, dH), 3.74 (d, 7= 3.3, IH, C₃H), 3.73 (d, 7= 3.3, IH, C₃H), 3.67 (s, 3H, -COOMe), 3.40 (s, 3H, OMe), 3.38 (s, 3H, OMe), 2.71 (dd, IH, 7 = 6.4, 14.6, C_αH'), 2.62 (dd, 7 =5.9, 14.6, IH, C_αH), 2.57 (dd, 7 = 5.2, 15.3, IH, C_αH'), 2.50 (dd, 7 = 4.2, 15.3, C_αH), 1.48 (s, 3H, Me), 1.46 (s, 3H, Me), 1.43 (s, 9H, -Boc), 1.31 (s, 3H, Me), 1.30 (s, 3H, Me). FAB MS: 619.1 (MT+ H) Part 2: Boc deprotectin of dipetide (Scheme 6; 36) Boc deprotection of 35 (0.92 g, 1.4 mmol) with TFA (1.4 mL) in CH₂C1₂ (14 mL) was performed according to GP-4 to give the amine salt 36. Part 3: Ester hydrolysis of dipeptide (Scheme 6; 37) Hydrolysis of ester 35 (1.05 g, 1.7 mmol) with 4N NaOH (6.7 mL) in methanol (6.7 mL) was performed according to GP-3 to give 37 (0.96 g, 92%) as a solid, M. p. 93-95 °C; [α] _D = -49.569 (c 0.39, CHC1₃), IR (KBr): 3361.5, 2992, 2939, 1707, 1506, 1354, 1159, 1074, 1008 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 6.91 (d, 7= 7.0 Hz, IH, S₂-NH), 5.53 (d, 7 = 8.8 Hz, IH, Ri-NH), 5.90 (d, 7= 3.9 Hz, IH, CiH), 5.89 (d, 7= 3.9 Hz, IH, dH), 4.59 (d, 7= 3.9 Hz, IH, C₂H), 4.55 (d, 7= 3.9Hz, IH, C₂H), 4.34 (m, IH, CpH), 4.33 (m, IH, dH), 4.32 (m, IH, CpH), 4.18 (d, 7= 3.1, IH, dH), 3.80 (d, 7= 3.1, IH, C₃H), 3.75 (d, 7 = 3.1, IH, C₃H), 3.41(s, 3H, OMe), 3.38 (s, 3H, OMe), 2.64 (m, 2H, C_αH,H), 2.60 (dd, 7 = 3.8,15.1, IH, C_αH'), 2.48 (dd, 7 = 7.8, 15.1, C_αH), 1.50 (s, 3H, Me), 1.47 (s, 3H, Me), 1.43 (s, 9H, -Boc), 1.32 (s, 3H, Me), 1.31 (s, 3H, Me). FAB MS: 605.2 (M⁺+ H) Part 4: Preparation of tetrapeptide (Scheme 6; 38) Acid 37 (0.98 g, 1.5 mmol) was treated with HOBt (0.24 g, 1.8 mmol), EDCI (0.34 g, 1.8 mmol), 36 (prepared by Boc deprotection of 35 (0.92 g, 1.5 mmol) with TFA (0.9 mL) in CH C1₂ (9 mL) according to GP-4) and DIPEA (0.4 mL, 2.23 mmol) according to GP-7 and purified by column chromatography (60-120 mesh Silica-gel, 2% Methanol- CHC1₃) to give 38 (1.36 g, 82.7%) as a white solid, M. p. 126 -128 °C; [α] _D = -2.96 (c 0.54, CHC13), IR (KBr): 3367, 2987, 2937, 1735, 1668, 1526, 1375, 1217, 1166, 1081, 1021 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 7.89 (d, 7= 9.6 Hz, IH, R₃-NH), 7.46 (d, 7= 8.5 Hz, IH, S₂-NH), 6.68 (d, 7 = 8.2 Hz, IH, S₄-NH), 6.04 (d, 7= 3.9 Hz, Hi CiH), 5.98 (d, 7 = 4.0 Hz, IH, CiH), 5.87 (d, 7= 3 9 Hz, IH, dH), 5.86 (d, 7= 3.9 Hz, IH, CiH), 5.10 (d, 7 = 10.6 Hz, IH, Ri-NH), 4.72 (m, IH, CpH), 4.57 (d, 7= 3.9 Hz, IH, C₂H), 4.55 (d, 7= 3.9 Hz, IH, C₂H), 4.53 (d, 7= 4.0 Hz, IH, C₂H), 4.51 (d, 7 = 3.9 Hz, IH, C₂H), 4.47 (m, IH, CpH), 4.46 (m, IH, dH), 4.41 (m, IH, CpH), 4.40 (m, IH, CpH), 4.31 (dd, 7= 3.3, 9.8 Hz, IH, dH), 4.16 (dd, 7= 3.2, 9.3 Hz, IH, dH), 4.14 (d, 7= 3.3 Hz, IH, C₃H), 3.96 (dd, 7 = 3.2, 8.2 Hz, IH, dH), 3.69 (d, 7= 3.2 Hz, IH, C₃H), 3.68 (d, 7= 3.2 Hz, IH, C₃H), 3.67 (d, 7= 3.2 Hz, Hi C₃H), 3.67(s, 3H, -COOMe), 3.37 (s, 3H, OMe), 3.35 (s, 3H, OMe), 3.34 (s, 3H, OMe), 3.33 (s, 3H, OMe), 2.97 (dd, 7= 2.9, 13.0 Hz, IH, C_αH'), 2.77 (dd, 7= 4.4, 15.5 Hz, IH, C_αH), 2.67 (dd, 7= 2.8, 14.8 Hz, IH, C_αH), 2.50 (dd, 7 = 5.2, 15.5 Hz, IH, C_αH'), 2.47 (dd, 7= 10.5, 14.8 Hz, IH, C_αH), 2.42 (dd, 7 = 4.7, 13.2 Hz, IH, C_αH), 2.18 (dd, 7= 2.6, 13.2 Hz, Hi C_αH'), 2.04 (dd, 7= 13.0, 13.0 Hz, IH, C_αH), 1.48 (s, 3H, Me), 1.47 (s, 3H, Me), 1.43 (s, 9H, Boc), 1.43 (s, 3H, Me), 1.43 (s, 3H, Me), 1.38 (s, 3H, Me), 1.30 (s, 3H, Me), 1.29 (s, 3H, Me), 1.28 (s, 3H, Me). FAB MS: 1105.4 (M⁺+ H) Part 5: Ester hydrolysis of tetrapeptide (Scheme 6; 39) Hydrolysis of ester 38 (L05 g, 0.95 mmol) with 4N NaOH (4 mL) in methanol (4 mL) was performed according to GP-3 to give 39 (0.93 g, 90%) as a solid, M. p. 144 -147 °C; [ ] D = +8.3868 (c 0.57, CHC1₃), IR (KBr): 3324, 2983, 2929, 1685, 1659, 1531, 1375, 1215, 1164, 1070, 1012 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 8.49 (d, 7= 9.5 Hz, IH, R₃-NH), 7.85 (d, 7= Hz, Hi S₂-NH), 6.35 (d, 7= 9.3 Hz, IH, S₄-NH), 5.91(d, 7= 3.9 Hz, IH, dH), 5.90(d, 7= 3.9 Hz, IH, CiH), 5.89 (d, 7= 3.9 Hz, IH, CiH), 5.87 (d, 7= 3.9 Hz, IH, dH), 5.34 (d, 7= 10.3 Hz, IH, Ri-NH), 4.59 (d, 7= 3.9 Hz, Hi C₂H), 4.55 (d, 7 = 3.9Hz, IH, C₂H), 4.49 (m, IH, CpH), 4.47 ( m, IH, CpH), 4.45(m, IH, dH), 4.40 (m , IH, CpH), 4.38 ( m, IH, CpH), 4.36 (m, IH, C₄H), 4.21 (m, IH, dH), 4.09 (m, IH, C₃H), 3.95 (m, IH, dH), 3.94 (d, 7= 3.1 Hz, IH, C₃H), 3.69 (d, 7= 3.0Hz,lH, C₃H), 3.65 (d, 7 =3.1Hz, IH, C₃H), 3.39 (s, 3H, OMe), 3.36 (s, 3H, OMe), 3.35 (s, 3H, OMe), 3.34 (s, 3H, OMe), 2.88 (m, IH, C_αH ), 2.81 (dd, 7= *, IH, C_αH'), 2.70 (dd, 7 = *, C_αH), 2.42 (dd, 7 = , C_αH), 2.39 (dd, 7= , C_αH), 2.37 (dd, 7= , C_αH'), 2.26 (dd, 7= , C_αH), 2.14 (dd, 7= , C_αH), 1.50 (s, 3H, Me), 1.49 (s, 3H, Me),1.44 (s, 3H, Me), 1.43 (s, 9H, -Boc), 1.37 (s, 3H, Me), 1.32 (s, 3H, Me), 1.31 (s, 6H, 2-Me), 1.29 (s, 3H, Me). FAB MS: 1091.2 (M"+ H) Part 6: Boc deprotectin of tetrapetide (Scheme 6; 40) Boc deprotection of 39 (0.061 g, 0.055 mmol) with TFA (0.1 mL) in CH₂C1₂ (1 mL) according to GP-4 gave 40.

At Part 7: Preparation of hexapeptide (Scheme 6; 41) Acid 39 (0.3 g, G.28mmol) was treated with HOBt (0.045 g, 0.33 mmol), EDCI (0.063 g, 0.33 mmol), 36 (prepared by Boc deprotection of 35 (0.17 g, 0.28 mmol) with TFA (0.2 mL) in CH₂C1₂ (2 mL) as described in GP-4) and DIPEA (0.07 mL, 0.4 mmol) according to GP-8 and purified by column chromatography (60-120 mesh Silica gel, 2.5% Methanol-CHCl₃) to give 41 (0.265 g, 60%) as a white solid, M. p. 164-167 °C; [α] D = +26.658 (c 0.29, CHC1₃), IR (KBr): 3291, 2987.5, 2937, 1734, 1652.5, 1542, 1376, 1217, 1165.5, 1081.5, 1021 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 8.61 (d, 7= 9.9 Hz, IH, R₃- NH), 8.46 (d, 7 = 9.7 Hz, IH, R₅-NH) 8.23 (d, 7 = 10.0 Hz, IH, S₂-NH), 7.41 (d, 7 = 7.3 Hz, IH, S₄-NH), 6.85 (d, 7= 8.2 Hz, IH, S₆-NH), 6.20 (d, 7= 3.7 Hz, IH, CiH), 6.12 (d, 7 = 3.8 Hz, IH, dH), 5.88 (d, 7= 3.6 Hz, Hi CiH), 5.87 (d, 7= 3.9 Hz, IH, dH), 5.86 (d, 7= 4.1 Hz, Hi CiH), 5.81 (d, 7= 3.8 Hz, IH, CiH), 5.47 (d, 7= 10.6 Hz, Hi Ri-NH), 4.81 (m, IH, CpH), 4.70 (m, IH, CpH), 4.61 (d, 7= 3.6 Hz, IH, C₂H), 4.57 (d, 7= 3.7 Hz, IH, C₂H), 4.56 (m, IH, CpH), 4.56 (d, 7 = 3.8 Hz, IH, C₂H), 4.55 (d, 7 = 4.1 Hz, IH, C₂H), 4.54 (d, 7 = 3.8 Hz, Hi, C₂H), 4.53 (m, IH, CpH), 4.47 (d, 7= 3.9 Hz, IH, dH), 4.42 (m, IH, CpH), 4.38 (dd, 7=3.2, 9.4 Hz, IH, dH), 4.36 (m, IH, CpH), 4.36 (m, IH, CiH), 4.34 (dd, 7= 3.1, 10.2 Hz, IH, dH), 4.19(d, 7= 3.2 Hz, IH, C₃H), 4.17 (dd, 7= 3.0, 9.7 Hz, IH, dH), 4.17 (d, 7= 3.2 Hz, IH, C₃H), 4.10 (dd, 7= 3.1, 9.9 Hz, IH, dH), 4.06 (dd, 7 = 3.4, 6.0 Hz, Hi dH), 3.76 (d, 7 = 3.0 Hz, IH, C₃H), 3.68 (d, 7 = 3.1 Hz, IH, C₃H), 3.66 (s, 3H, -COOMe), 3.67 (d, 7= 3.4 Hz, Hi C₃H), 3.62 (d, 7= 3.1 Hz, Hi C₃H), 3.41 (s, 3H, OMe), 3.38 (s, 3H, OMe), 3.36 (s, 3H, OMe), 3.32 (s, 3H, OMe), 3.32 (s, 3H, OMe), 3.30 (s, 3H, OMe), 3.13 (dd, 7= 2.1, 12.8 Hz, IH, C_αH'), 2.82 (dd, 7 = 4.6, 15.4 Hz, IH, C_αH), 2.77 (dd, 7= 2.6, 12.5 Hz, IH, C_αH'), 2.68.(dd, 7= 2.4, 15.2 Hz, IH, C_αH'), 2.53 (dd, 7= 11.8, 15.2 Hz, Hi C_αH), 2.52 (dd, 7= 5.4, 12.8 Hz, IH, C_αH), 2.50 (dd, 7 = 5.5, 15.4 Hz, Hi C_αH), 2.29 (dd, 7= 5.0, 12.8 Hz, IH, C_αH), 2.25 (dd, 7= 3.2, 12.8 Hz, IH, C_αH'), 2.20 (t, 7 = 12.8 Hz, IH, C_αH), 2.11 (t, 7 = 12.5 Hz, IH, C_αH), 2.05 (dd, 7 = 2.7, 12.8 Hz, IH, C_αH'), 1.50 (s, 3H, Me), 1.46 (s, 3H, Me), 1.45 (s, 3H, Me), 1.44 (s, 3H, Me), 1.42 (s, 9H, Boc), 1.36 (s, 3H, Me), 1.33 (s, 3H, Me), 1.31 (s, 3H, Me), 1.28 (s, 3H, Me), 1.28 (s, 3H, Me), 1.28 (s, 3H, Me), 1.27 (s, 3H, Me), 1.26 (s, 3H, Me). FAB MS: 1592.5 (M⁺+ H)

Part 8: Preparation of octapeptide (Scheme 6; 42) Acid 39 (0.06 g, 0.055 mmol) was treated with HOBt (0.009 g, 0.07 mmol), EDCI (0.013 g, 0.07 mmol), 40 (prepared by Boc deprotection of 38 (0.061 g, 0.055 mmol) with TFA (0.1 mL) in CH₂C1₂ (1 mL) according to GP-4) and DIPEA (0.015 mL, 0.08 mmol) according to GP-9 and purified by column chromatography (60-120 mesh Silica-gel, 3% Methanol-CHCl₃) to give 42 (0.051 g, 45%) as a white solid, M. p. 164-167 °C; [α] D = +19.581(c 0.23, CHC1₃), IR (KBr): 3283, 2988, 2935, 1648, 1560, 1376, 1214, 1166, 1081, 1022 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 8.92 (d, 7=10.1 Hz, IH, R₅-NH), 8.60 (d, 7= 10.1 Hz, IH, Ra-NH), 8.596 (d, 7= 10.0 Hz, IH, R₇-NH), 8.29 (d, 7= 9.3 Hz, IH, S₄- NH), 7.94 (d, 7 = 10.2 Hz, IH, S₂-NH), 7.42 (d, 7= 8.2 Hz, IH, S₆-NH), 6.88(d, 7 = 8.2 Hz, IH, S₈-NH), 6.12(d, 7= 3.7 Hz, IH, CiH), 6.08 (d, 7= 3.8 Hz, IH, CiH), 5.89 (d, 7 = 3.6 Hz, IH, CiH), 5.89 (d, 7= 3.6 Hz, IH, dH), 5.88 (d, 7= 3.9 Hz, IH, CiH), 5.87 (d, 7 = 4.1 Hz, IH, CiH), 5.87 (d, 7= 4.1 Hz, IH, CiH), 5.82 (d, 7= 3.8 Hz, IH, H), 5.35 (d, 7= 8.5 Hz, IH, Ri-NH), 4.77 (m, IH, CpH), 4.75 (m, IH, CpH), 4.66 (m, IH, CpH), 4.58 (d, 7= 3.8 Hz, IH, C₂H), 4.57 (d, 7= 3.7 Hz, Hi C₂H), 4.57 (d, 7 = 3.7 Hz, IH, C₂H), 4.56 (d, 7 = 3.9 Hz, IH, C₂H), 4.55 (d, 7 = 3.8 Hz, IH, C₂H), 4.55 (d, 7 = 3.8 Hz, Hi C₂H), 4.51 (m, IH, CpH), 4.51 (d, 7= 3.8 Hz, IH, C₂H), 4.50 (m, IH, CpH), 4.44 (m, IH, CpH), 4.43 (d, 7 = 3.8 Hz, IH, C₂H), 4.42 (dd, 7 =3.2, 9.4 Hz, IH, C4H), 4.38(m, IH, CpH), 4.36 (m, IH, CpH), 4.33 (dd, 7= 3.1,9.4 Hz, Hi dH), 4.30 (dd, 7 = 3.2, 9.7 Hz, IH, dH), 4.22 (m, IH, C₄H), 4.16 (dd, 7 = 3.2, 9.6 Hz, Hi dH), 4.16 (dd, 7= 3.1, 9.7 Hz, IH, dH), 4.15(d, 7= 3.2 Hz, IH, C₃H), 4.12 (d, 7= 3.2 Hz, IH, C₃H), 4.10 (dd, 7 = 3.1, 10.0 Hz, IH, dH), 4.04 (dd, 7= 3.2, 6.7 Hz, IH, dH), 3.73 (d, 7= 3.0 Hz, IH, C₃H), 3.73 (d, 7= 3.0 Hz, IH, C₃H), 3.67 (s, 3H, -COOMe), 3.66 (d, 7= 3.2 Hz, IH, C₃H), 3.65 (d, 7= 3.1 Hz, IH, C₃H), 3.61 (d, 7= 3.1 Hz, IH, C₃H), 3.39 (s, 3H, OMe), 3.38 (s, 3H, OMe), 3.37 (s, 3H, OMe), 3.36 (s, 3H, OMe), 3.35 (s, 3H, OMe), 3.34(s, 3H, OMe), 3.33 (s, 3H, OMe), 3.25 (s, 3H, OMe), 2.97 (dd, 7= 1.5, 12.8 Hz, IH, C_αH'), 2.89 (dd, 7= 2.2, 12.8 Hz, IH, C_αH), 2.88 (dd, 7= 2.2, 12.2 Hz, IH, C_αH), 2.81(m,lH, C_αH'), 2.67 (dd, 7 = 1.9, 12.1Hz, IH, C_αH'), 2.56 (dd, 7= 1 1.8, 15.2 Hz, IH, C_αH), 2.55 (dd, 7= 5.4, 12.8 Hz, IH, C„H), 2.48 (dd, 7 = 5.5, 15.4 Hz, IH, C_αH), 2.42 (dd, 7 = 5.5, 15.4 Hz, IH, C_αH), 2.36 (dd, 7 = 5.0, 12.8 Hz, IH, C_αH), 2.32 (dd, 7 = 3.2; 12.8 Hz, IH, C_αH'), 2.28 (t, 7 = 12.8 Hz, IH, C_αH), 2.26 (t, 7= 12.5 Hz, IH, C_αH), 2.16 (dd, 7= 2.7, 15.4 Hz, IH, C_αH'), 2.09 (dd, 7= 2.7, 12.8 Hz, IH, C_αH'), 2.05 (dd, 7= 2.7, 12.8 Hz, IH, C_αH'), 1.50 (s, 3H, Me), 1.46 (s, 3H, Me), 1.45 (s, 3H, Me), 1.44 (s, 3H, Me), 1.42 (s, 9H, Boc), 1.36 (s, 3H, Me), 1.33 (s, 3H, Me), 1.31 (s, 3H, Me), 1.28 (s, 3H, Me), 1.28 (s, 3H, Me), 1.28 (s, 3H, Me), 1.27 (s, 3H, Me), 1.26 (s, 3H, Me). FAB MS: 2078.4 (M*+ H) Part 9: Preparation of tripeptide (Scheme 6; 43) Acid 37 (0.15 g, 0.25 mmol) was treated with HOBt (0.04 g, 0.3 mmol), EDCI (0.06 g, 0.3 mmol), 10 (prepared by Boc deprotection of 8a (0.094 g, 0..25 mmol) with TFA (0.1 mL) in CH₂C1₂ (1.0 mL) according to GP-4) and DIPEA (0.06 mL, 0.37 mmol) according to GP-6 and purified by column chromatography (60-120 mesh Silica-gel, 70% EtOAc-pet. ether) to give 43 (0.16 g, 75.1%) as a white solid, M. p. 108-111 °C; [α] _D 5.103 (c 0.45, CHCb), IR (KBr): 3364, 3308, 2996, 2940, 1717, 1670, 1542, 1371, 1164, 1077, 1010 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 8.08 (d, 7= 9.5 Hz, IH, R₃-NH), 7.19 (d, 7= 9.6 Hz, IH, S₂-NH), 5.89 (d, 7= 3.8 Hz, IH, CiH), 5.89 (d, 7= 3.8 Hz, IH, CiH), 5.85 (d, 7= 3.8 Hz, IH, CiH), 5.26 (d, 7= 10 5 Hz, IH, R_X-NH), 4.69 (m, IH, CpH), 4.57 (d, 7 = 3.8Hz, IH, C₂H), 4.53 (d, 7= 3.8Hz, IH, C₂H), 4.53 (m, IH, CpH), 4.52 (d, 7= 3.8Hz, IH, C₂H), 4.50 (m,lH, CpH), 4.30 (dd, 7= 7.6, 3.2 Hz, IH, dH), 4.17 (dd, 7= 7.5, 3.2 Hz, IH, dH), 4.13 (d, 7= 3.1 Hz, IH, C₃H), 3.99 (dd, 7= 6.8,3.2 Hz, IH, dH), 3.71 (d, 7 = 3.3 Hz, IH, C₃H), 3.70 (d, J= 3.2 Hz, IH, C₃H), 3.66 (s, 3H, COOMe), 3.39(s, 3H, OMe), 3.38 (s, 3H, OMe), 3.36(s, 3H, OMe), 2.78 (dd, J= 2.7,12.4 Hz, Hi CJf), 2.53 {m, 2H, C_αH,H'), 2.34 (dd, J= 4.9,13.1 Hz,lH, C_αH), 2.22 (dd, J=3.3, 13.1, IH, C_αH'), 2.16 (dd, J= 12.4,12.9 Hz, IH, C_αH'), 1.44 (s, 6H, 2 X Me), 1.43 (s, 9H, -Boc), 1.39 (s, 3H, Me), 1.306 (s, 3H, Me), 1.298 (s, 3H, Me), 1.29 (s, 3H, Me). EXAMPLE -6 Part 1 : Preparation of tetrapeptide (Scheme 7; 44) Acid 22 (0.1 g, 0.165 mmol) was treated with HOBt (0.027 g, 0.2 mmol), EDCI (0.038 g, 0.2 mmol), 36 (prepared by Boc deprotection of 35 (0.105 g, 0.165 mmol) with

TFA (0.1 mL) in CH₂C1₂ (1 mL) according to GP-4) and DIPEA (0.065 mL, 0.25 mmol) according to GP-7 and purified by column chromatography (60-120 mesh Silica-gel, 2% Methanol-CHCl₃) to give 44 (0.135 g, 73.9%) as a white solid, M. p. 112 -115 °C; [α] _D

= -43.619 (c 0.36, CHCB), IR (KBr): 3388, 2988, 2941, 1718, 1675, 1521, 1368, 1164, 1070, 1021 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 7.24 (d, 7= 9.3 Hz, IH, R2-NH), 7.07 (d,

7= 9.3 Hz, IH, R3-NH), 6.95 (d, 7= 8.4 Hz, IH, S4-NH), 5.88 (d, 7 = 3.9 Hz, IH, CiH),

5.88 (d, 7 = 4.0 Hz, IH, C,H), 5.90 (d, 7 = 3.9 Hz, IH, dH), 5.87 (d, 7 = 3.9 Hz, IH, dH), 5.54 (d, 7= 9.7 Hz, IH, SI-NH), 4.64 (m, IH, CpH), 4.57 (d, 7= 3.9 Hz, IH, C₂H),

4.55 (m, IH, CpH), 4.55 (d, 7= 3.9 Hz, IH, C₂H), 4.53 (d, 7= 4.0 Hz, IH, C H), 4.53 (d, 7

= 3.9 Hz, IH, C₂H), 4.49 (m, IH, CpH), 4.42 (dd, 7= 3.2, 8.1 Hz, IH, dH), 4.31 (dd, 7 =

3.3, 7.6 Hz, IH, dH), 4.30 (dd, 7= 3.2, 7.8 Hz, IH, GOT), 4.24 (m, IH, CpH), 4.21 (dd, 7 = 3.2, 7.9 Hz, IH, dH), 3.74 (d, 7= 3.3 Hz, IH, C₃H), 3.67 (d, 7= 3.0 Hz, IH, C₃H), 3.68 (s, 3H, -COOMe), 3.67 (d, 7= 3.2 Hz, IH, C₃H), 3.64 (d, 7 = 3.2 Hz, IH, C₃H), 3.39 (s, 3H, OMe), 3.38 (s, 3H, OMe), 3.37 (s, 3H, OMe), 3.36 (s, 3H, OMe), 2.66 (d, 7= 6.0 Hz, 2H, C_αH,H'), 2.57 (dd, 7= 5.4, 14.5 Hz, IH, C_«H), 2.55 (m,lH, C_αH), 2.53 (m, IH, C_«H), 2.47 (m, IH, C_αH), 2.44 (dd, 7= 4.2, 14.5 Hz, IH, C_αH), 2.44 (m, IH, C_αH'), 1.47 (s, 3H, Me), 1.45 (s, 3H, Me), 1.446 (s, 6H, 2-Me), 1.446 (s, 3H, Me), 1.42 (s, 9H, Boc), 1.31 (s, 3H, Me), 1.30 (s, 3H, Me), 1.29 (s, 3H, Me). FAB MS: 1105.2 (M^÷+ H) Part 2: Preparation of tetrapeptide (Scheme.7; 45) Acid 37 (0.07 g, 0.116 mmol) was treated with HOBt (0.02 g, 0.14 mmol), EDCI (0.027 g, 0.14 mmol), 21 (prepared by Boc deprotection of 20 (0.072 g, 0.125 mmol) with TFA (0.1 mL) in CH₂C1₂ (1 mL) according to GP-4) and DIPEA (0.03 mL, 0.17 mmol) according to GP-7 and purified by column chromatography (60-120 mesh Silica-gel, 2% Methanol-CHCl₃) to give 45 (0.102 g, 79.7%) as a white solid, M. p. 118 -121 °C; [α] _D = -26.569 (c 0.5, CHC13), IR (KBr): 3387, 2987, 2940, 1724, 1662, 1538, 1377, 1158, 1080, 1013 cm^"1; 1H-NMR(500 MHz, CDC1₃) δ 7.29 (d, 7= 9.0 Hz, IH, S3-NH), 7.05 (d, 7= 9.1 Hz, IH, R4-NH), 6.84 (d, 7 = 8.9 Hz, IH, S2-NH), 5.90 (d, 7= 4.0 Hz, Hi CiH), 5.88 (d, 7 = 3.9 Hz, Hi C,H), 5.88 (d, 7 = 3.9 Hz, IH, CiH), 5.87 (d, 7 = 3.9 Hz, IH, CiH), 5.63 (d, 7= 9.8 Hz, IH, RI-NH), 4.65 (m, IH, CpH), 4.57 (d, 7= 3.9 Hz, IH, C₂H), 4.55 (d, 7 = 3.9 Hz, IH, C₂H), 4.53 (d, 7 = 4.0 Hz, IH, C₂H), 4.53 (d, 7 = 3.9 Hz, IH, C₂H), 4.52 (m, IH, CpH), 4.48 (m, IH, CpH), 4.36 (m, Hi CpH), 4.34 (dd, 7= 3.3, 7.7 Hz, IH, C₄H), 4.28 (dd, 7= 3.2, 7.3 Hz, IH, dH), 4.22 (dd, 7 = 3.2, 8.7 Hz, Hi dH), 4.18 (dd, 7 = 3.2, 7.6 Hz, IH, C₄H), 3.95 (d, 7 = 2.9 Hz, IH, C₃H), 3.76 (d, 7 = 3.1 Hz, IH, C₃H), 3.74 (d, 7= 3.0 Hz, IH, C₃H), 3.72 (d, 7= 2.8 Hz, IH, C₃H), 3.68 (s, 3H, -COOMe), 3.39 (s, 3H, OMe), 3.38 (s, 3H, OMe), 3.37 (s, 3H, OMe), 3.36 (s, 3H, OMe), 2.69 (dd, 7= 4.8, 15.5 Hz, IH, C_αH'), 2.63 (dd, 7= 7.0, 15.5 Hz, IH C_αH), 2.56 (dd, 7= 4.2, 14.6 Hz, IH, C„H'), 2.48 (dd, 7 = 6.5, 15 Hz, IH, C„H), 2.46 (m, lH, C_αH), 2.40 (dd, 7 = 4.8, 15.0 Hz, IH, C_αH), 2.43 (m, IH, C_αH'),_.2.43 (m, IH, C_αH), 1.47 (s, 3H, Me), 1.45 (s, 3H, Me), 1.42 (s, 9H, Boc), 1.46 (s, 3H, Me), 1.46 (s, 3H, Me), 1.31 (s, 3H, Me), 1.30 (s, 3H, Me), 1.29 (s, 3H, Me), 1.29 (s, 3H, Me). FAB MS: 1105.1 (M⁺+ H) EXAMPLE -7

Part 1: Preparation of dipeptide (Scheme 8; 47) Acid 6 (0.45 g, 1.25 mmol) was treated with HOBt (0.202 g, 1.5 mmol), EDCI (0.287 g, 1.5 mmol) and 46 (prepared by neutralization of β-alanine methyl ester salt (0.174 g, 4.57 mmol) with DIPEA (0.32 mL, 1.87 mmol), according to GP-5 and purified by column chromatography (60-120 mesh Silica-gel, 60% EtOAc-pet ether) to give 47 (0.475 g, 85.6%) as a white solid, M. p. 140 -142 °C; [α] _D = -38.236 (c 0.5,CHC13), IR (KBr): 3355, 2981, 1744.5, 1693, 1651, 1528, 1370, 1250, 1172, 1076, 1022 cm^"1; 1H- NMR (500 MHz, CDC1₃) δ 6.59 (bs, IH, Ala-NH), 5.90 (d, 7= 3.9 Hz, IH, CiH), 5.13 (bs, IH, SI-NH), 4.58 (d, 7= 3.9Hz, IH, C₂H), 4.27 (dd, 7= 7.7, 3.2, IH, dH), 4.14 (m, IH, CpH), 3.73 (d, 7 = 3.2, IH, C₃H), 3.70 (s, 3H, COOMe), 3.51 (q, 7= 6.1 Hz, 2H, CpH), 3.37(s, 3H, OMe), 2.54 (t, 7= 6.1 Hz, 2H, C_αH,H'), 2.52 (dd, 7= 5.9,14.8, IH, C_αH), 2.46 (dd, 7= 6.0, 14.8, C_αH'), 1.48 (s, 3H, Me), 1.43 (s, 9H, -Boc), 1.32 (s, 3H, Me). FAB MS: 447.2 (M⁺+ H) Part 2: Boc deprotectin of dipetide (Scheme 8; 48) Boc deprotection of 47 (0.134 g, 0.30 mmol) with TFA (0.15 mL) in CH₂C1₂ (1.5 mL) was performed according to GP-4 to give the amine salt 48. Part 3: Ester hydrolysis of dipeptide (Scheme 8; 49) Hydrolysis of ester 47 (0.225 g, 0.505 mmol) with 4N NaOH (2 mL) in methanol (2 mL) was performed according to GP-3 to give 49 (0.19 g, 88.1%) as a solid, M. p. 147-149 °C; [α] _D = -41.7555 (c 0.6, CHC1₃), IR (KBr): 3354, 2981, 1692, 1648, 1528, 1370, 1251, 1168, 1076, 1021 cm^"1; 1H-NMR (500 MHz, CDC1₃) δ 7.11 (bs, IH, Ala-NH), 5.90 (d, 7 = 3.9 Hz, IH, CyH), 5.23 (bs, IH, SI-NH), 4.58 (d, 7= 3.9Hz, IH, C₂H), 4.33 (m, IH, dH), 4.15 (m, IH, CpH), 3.73 (d, 7= 3.2, IH, C₃H), 3.52 (m, 2H, CpH), 3.37(s, 3H, OMe), 2.57 (t, 7 = 6.1 Hz, 2H, C_αH,H), 2.49 (m, 2H, C_αH,H'), 1.48 (s, 3H, Me), 1.43 (s, 9H, -Boc), 1.32 (s, 3H, Me). FAB MS: 433.2 (M⁺+ H) Part 4: Preparation of tetrapeptide (Scheme 8; 50) Acid 49 (0.13 g, 0.3 mmol) was treated with HOBt (0.05 g, 0.36 mmol), EDCI (0.05 g, 0.36 mmol), 48 (prepared by Boc deprotection of 47 (0.134 g, 0.3 mmol) with TFA (0.15 mL) in CH₂C1₂ (1.5 mL) according to GP-4) and DIPEA (0.08 mL, 0.45 mmol) according to GP-7 and purified by column chromatography (60-120 mesh Silica-gel, 3% Methanol-CHCl₃) to give 50 (0.18 g, 78.7%) as a white solid, M. p. 184 -186 °C; [α] _D = -64.635 (c 0.6, CHC13), IR (KBr): 3336, 2984, 2937, 1740, 1690, 1654, 1542, 1372, 1254, 1168, 1079, 1020 cm^"1; FAB MS: 761.3 (M^τ+ H)

Part 5: Ester hydrolysis of tetrapeptide (Scheme 8; 51) Hydrolysis of ester 50 (0.5 g, 0.66 mmol) with 4N NaOH (2.5 mL) in methanol (2.5 mL) was performed according to GP-3 to give 51 (0.43 g, 87.6%) as a solid, M. p. 165 - 168 °C; IR(KBr): 3317, 2988, 2941, 1717, 1647, 1537, 1364, 1247, 1160, 1074, 1011 cm^"1; Part 6: Preparation of hexapeptide (Scheme 8; 52) Acid 51 (0.2 g, 0.27mmol) was treated with HOBt (0.04 g, 0.32 mmol), EDCI (0.06 g, 0.32 mmol), 48 (prepared by Boc deprotection of 47 (0.12 g, 0.27 mmol) with TFA (0.1 mL) in CH₂C1₂ (1 mL) as described in GP-4) and DIPEA (0.07 mL, 0.4 mmol) according to GP-8 and purified by column chromatography (60-120 mesh Silica gel, 4% Methanol-CHCl₃) to give 52 (0.155 g, 53.8%) as a white sohd, M. p. 220-223 °C; IR (KBr): 3301, 2978, 2932, 1656, 1547, 1368, 1173, 1081, 1025 cm^"1. REFERENCES

Gellman et al, 7. Am. Chem. Soc, 116, 1054-1062 (1994) Seabach et al, Helv. Chim. Ada,. 79, 913-941 and 2043-2066 (1996)

Gellman et al, 7 Am. Chem. Soc, 118, 13071-72 (1996) Gellman et al, Nature, 387, 381 (1997)

Gellman et al, US Patent 6,060,5^*85 (2000)

Seebach et al, Helv. Chim. Ada,. 81, 932 (1998)

Seebach et al, Helv. Chim. Acta,. 81, 2218-2243(1998)

Schweizer, A gew. Chem. Int. K, 41, 230-253 (2002) Kessler et al, Chem. Rev., 102, 491-514 (2002)

Kessler et al, Chem. Eur. 7, 8, 4366-4376 (2002)

Sharma et al, Tetrahedron: Asymm., 13, 21-24, (2002)

Dhawale et al, 7 Org. Chem., 16, 1065, 2001

Bodanszky et al, The practice of Peptide Synthesis, Springer Nerlag, New York, 1984 Cavanagh et al, Protein NMR Spectroscopy, Academic Press, San Diego, 1996

Wuthrich et al, NMR of Proteins and Nucleic Acids, Wiley, New York, 1986

States et al, 7 Magn. Reson. 48, 286-292, 1982

Claims

WE CLAIM: 1. C-linked β-peptides (oligomers) compounds of the formula I

Formula I wherein 0, 1, 2, 3. R= H, Boc, Cbz, Fmoc, acetyl or salts such as HCl, TFA and others Rⁱ⁼ -O alkyl, -O-aralkyl, -amine, alkylamine, aryalkyl maine R² = R³ = R⁴= R³ =H R² = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R³ = R⁴= R⁵ =H R³ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R² = R⁴ = R⁵ =H R = sugar or hydroxy alkyl, amino alkyl thioalkyl, R² = R³ = R⁵ =H R⁵= sugar or hydroxy alkyl, amino alkyl/thioalkyl, R²= R³ = R⁴ =H R² = R⁴ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R³ = R⁵ =H R³ = R⁵ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R² = R⁴ =H R² = R⁵ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R³ = R⁴ =H R³ = R⁴ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R² = R⁵ =H R² = R³ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R⁴ = R⁵ =H R⁴ = R⁵ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R² = R³ =H 2. A compound as claimed in claim 1 wherein the sugar comprises a monosaccharide pentose selected from the group consisting of D-xylo, D-ribo, D-lyxo, O-ara; a L- sugar selected from the group consisting of L-xyl, L-rib, L-lyxo, L-ara in furanoside or pyranoside form; a hexose selected from the group consisting of D and L-glc, D and L-gal, D and L- a , D and L-gul, D and L-all, etc. in furanoside/ pyranoside form; a disaccharide selected from the group consisting of lactose, maltose and cellobiose; and fully protected as acetates, benzoates, allyl or aralkyl ethers, alkylidene dioxolane derivatives, thio derivatives or totally unprotected sugars, D and L sugars in furanoside/pyranoside form having heterocyclic bases such as adenine, guanine, thymidine, cytosine or unnatural bases or heterocyclics having one or more than one heteroatoms such as O/N/S both in 5 and 6 membered rings, dexoy sugars/amino sugars natural/non-natural, rare sugars and higher sugars, bifunctional sugar amino acids. A C-linked carbo β-peptids compound as claimed in claim 1, wherein the compound has a structural formula shown below:

A C-linked carbo β-peptide compound as claimed in claim 1, wherein the compound has a structural formula shown below:

5. A C-linked carbo β-peptide compound as claimed in claim 1, wherein the compound has a structural formula shown below:

A C-linked carbo β-peptide compound as claimed in claim 1, wherein the compound has a structural formula shown below:

A C-linked carbo β-peptide compound as claimed in claim 1, wherein the compound has a structural formula shown below:

A C-linked carbo β-peptide compound as claimed in claim 1, wherein the compound has a structural formula shown below:

A C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

10. A C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

11. A C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

12. A C-linked carbo β-peptide compound as claimed in claim 1, wherein compound a has structural formula shown below:

13. A C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

14. A C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

15. A C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown ebelow:

16. A C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

17. A C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

18. A C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

19. A C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

20. A C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

21. A C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

22. A C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

23. C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

24. C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

25. C-linked carbo β-peptide compound as -claimed in claim 1, wherein compound has a structural formula shown below:

26. C-linked carbo β-peptides compound as claimed in claim 1, wherein compound has a structural formula shown below:

27. C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

28. C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

29. C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

30. C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown belo.w:

33. C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

34. C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

35. C-iinked carbo β-peptide compound as claimed in claim 1, wherem compound has a structural formula shown below:

56. C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

37. C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

38. C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

40. C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

41. C-linked carbo β-peptide compound as claimed in claim 1, wherein compound has a structural formula shown below:

42. A method for preparation of a C-linked carbo β-peptide compound of formula 1 with stable helical secondary structures,

Formula I wherein n= 0, 1, 2, 3 R= H, Boc, Cbz, Fmoc, acetyl or salts such as HCl, TFA and others R¹⁼ -O alkyl, -O-aralkyl, -amine, alkylamine, aryalkyl maine R² = R³ = R⁴= R⁵ =H R² = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R³ = R⁴= R⁵ =H R³ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R² = R⁴ = R⁵ =H R⁴= sugar or hydroxy alkyl, amino alkyl/thioalkyl, R² = R³ = R⁵ =H R⁵= sugar or hydroxy alkyl, amino alkyl/thioalkyl, R² = R³ = R⁴ =H R² = R⁴ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R³ = R⁵ =H R³ = R⁵ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R² = R⁴ =H R² = R⁵ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R³ = R⁴ =H R³ = R⁴ = sugar or hydroxy alkyl, amino alkyl/thioalkyl, R² = R⁵ =H R² = R³ = sugar or hydroxy alkyl, amino .alkyl/thioalkyl, R⁴ = R⁵ =H R⁴ = R⁵ = sugar or hydroxy alkyl, amino alkyl thioalkyl, R² = R³ =H the method comprising: a) reacting C-linked carbo β-amino acid ester with Pd-C and exposing it to (Boc)₂ to give N-Boc C-linked carbo β-amino acid ester b) aqueous alkaline hydrolysis of C-linked carbo β-amino acid ester to give the C- linked carbo β-amino acid c) acid mediated hydrolysis of C-linked carbo β-amino acid ester to give the salt of C- linked β-amino acid ester d) reacting the C-linked carbo β-amino acid with amine of C-linked carbo β-amino acid ester under normal peptide conditions to give dipeptide e) alkaline hydrolysis of dipeptide to give dipeptide acid f) acid hydrolysis of dipeptide to give the dipeptide amine salt g) reacting dipeptide acid with monomer amine salt to give tripeptide h) reacting dipeptide acid with dipeptide salt to give tetrapeptide i) alkaline hydrolysis of tetrapeptide to tetrapeptide acid j) acid hydrolysis of tetrapeptide to tetrapeptide amine salt k) reacting tetrapeptide acid with dipeptide amine salt to give the hexapeptide I) reacting tetrapeptide acid with tetrapeptide amine salt to give the octapeptide

43. A method as claimed in claim 43 wherein the C-linked carbo β-amino acid ester is a (S)-epimer or the (R)-epimer at the amine centre.

44. A method as claimed in claim 43 wherein the alkaline hydrolysis is carried out on a C-linked carbo β-amino acid ester with (S)-amine centre or C-linked carbo β-amino acid ester with (R)-amine centre 45. A method as claimed in claim 43 wherein the acid hydrolysis is carried out on C- linked carbo β-amino acid ester with (S) amine centre or C-linked carbo β-amino acid ester with (R) amine centre 46 A method as claimed in claim 43 wherein the peptide coupling is carried out on (a) with C-linked carbo β-amino acid having (S) amine centre with C-linked carbo β-amino acid ester with (S) amine salt to give SS dipeptide (b) with C-linked carbo β-amino acid having (S) amine centre with C-linked carbo β-amino acid ester with (R) amine salt to give SR dipeptide (c) with C-linked carbo β-amino acid having (R) amine centre with C-linked carbo β-amino acid ester with (R) amine salt to give RR dipeptide (d) with C-linked carbo β-amino acid having (R) amine centre with C-linked carbo β-amino acid ester with (S) amine salt to give RS dipeptide (e) with C-linked carbo β-amino acid having (S) amine with β-Alanine ester having amine salt to give C-linked carbo β-amino acid-β-Alanine mixed dipeptide

47. A method as claimed in claim 43 wherein the alkaline hydrolysis is carried out by a) SS dipeptide to give SS dipeptide acid b) SR dipeptide to give SR dipeptide acid c) RR dipeptide to give RR dipeptide acid d) RS dipeptide to give RS dipeptide acid

48. A method as claimed in claim 43 wherein the acid hydrolysis is carried out on a) SS dipeptide to give SS dipeptide salt b) SR dipeptide to give SR dipeptide salt c) RR dipeptide to give RR dipeptide salt d) RS dipeptide to give RS dipeptide salt

49. A method as claimed in claim 43 wherein the peptide coupling is carried out to give tripeptide a) with SS dipeptide acid with C-linked carbo β-amino acid ester (S) amine salt b) with SR dipeptide acid with C-linked carbo β-amino acid ester (S) amine salt

50. A method as claimed in claim 43 wherein the peptide coupling is carried out to give tetrapeptide a) with SS dipeptide acid and SS dipeptide amine salt to give SSSS tetrapeptide b) with SR dipeptide acid and SR dipeptide amine salt to give SRSR tetrapeptide c) with RR dipeptide acid and RR dipeptide amine salt to give RRRR tetrapeptide d) with RS dipeptide acid and RS dipeptide amine salt to give RSRS tetrapeptide e) with RS dipeptide acid and SR dipeptide amine salt to give RSSR tetrapeptide f) with SR dipeptide acid and RS dipeptide amine salt to give SRRS tetrapeptide g) with mixed dipeptide acid and mixed dipeptide salt to give mixed S-βAlanine-S- β-alanine tetrapeptide 51. A method as claimed in claim 43 wherein the alkaline hydrolysis is carried out on tetrapeptides such as a) SSSS tetrapeptide to give SSSS tetrapeptide acid b) SRSR tetrapeptide to give SRSR tetrapeptide acid c) RRRR tetrapeptide to give RRRR tetrapeptide acid d) RSRS tetrapeptide to give RSRS tetrapeptide acid e) S-β-alanineS-β-alanine mixed tetrapeptide acid

52. A method as claimed in claim 43 wherein the acid hydrolysis is carried out on tetrapeptides such as a) SSSS tetrapeptide to give SSSS tetrapeptide amine salt b) SRSR tetrapeptide to give SRSR tetrapeptide amine salt c) RRRR tetrapeptide to give RRRR tetrapeptide amine salt d) RSRS tetrapeptide to give RSRS tetrapeptide amine salt e) mixed tetrapeptides to give mixed tetrapeptide amine salt

53. A method as claimed in claim 43 wherein the hexapeptides are prepared from a) SS tetrapeptide acid and SS dipeptide amine salt to give SSSSSS hexapeptide b) SR tetrapeptide acid and SR dipeptide amine salt to give SRSRSR hexapeptide c) RR tetrapeptide acid and RR dipeptide amine salt to give RRRRRR hexapeptide d) RS tetrapeptide acid and RS dipeptide amine salt to give RSRSRS hexapeptide e) mixed tetrapeptide acid and mixed dipeptide amine salt to give mixed hexapeptide 54. A method as claimed in claim 43 wherein the coupling of tetrapeptides are carried out to give octapeptide such as a) SSSS tetrapeptide acid and SSSS tetrapeptide amine salt to give octapeptide b) SRSR tetrapeptide acid and SRSR tetrapeptide amine salt to give octapeptide c) RRRR tetrapeptide acid and RRRR tetrapeptide amine salt to give octapeptide d) RSRS tetrapeptide acid and RSSS tetrapeptide amine salt to give octapeptide

55. A method as claimed in claim 43 wherein the C-liked carbo β-peptide is represented by the following formula

56. A method as claimed in claim 43 wherein the C-linked carbo β-peptides are nonnatural β-peptides