Umsetzungen von tert.-Butyloxycarbonylfluorid mit trifunktionellen Aminosäuren

An improved synthesis of tert-butyloxycarbonyl-L-histidine

In our investigations on the effect of replacement of histidine by homohistidine (1) on the biological activity of some peptide-hormones, relatively large quantities of Boc-homohistidine were required. Homohistidine being difficult to synthesize, it was essential to find an effective way of introducing the Boc-group. In the past, many syntheses of Boc-histidine were reported (2-6), none of which proved to be quite satisfactory. However, by modifying the procedure of Flouret et al. (6) a convenient method resulting in a high yield of Boc-histidine and Boc-homohistidine was found.

New methods for side-chain protection of cysteine

[reaction: see text]. Cysteine sulfhydryl protection with either the Fmoc or the Fm group was accomplished in one step and in high yield using commercially available FmocCl or FmocOSu, respectively. Mechanisms for the Fmoc to Fm transformations are discussed. Additionally, Fmoc-Cys(Fmoc)-OH (7) was synthesized and used in amide bond forming reactions. The S-Fmoc group is cleaved selectively from peptides containing the N-Fmoc group.

Solid-phase synthesis of chicken vasoactive intestinal peptide by a mild procedure using N alpha-9-fluorenylmethyloxycarbonyl amino acids

The octacosapeptide amide corresponding to the entire amino acid sequence of chicken vasoactive peptide (VIP) was assembled on a p-benzyloxybenzylamine resin support using the base-labile 9-fluorenylmethyloxycarbonyl as N alpha-protecting group, cleaved by mild acid treatment, and purified by gel-filtration and ion-exchange chromatography. The symmetrical anhydride coupling was employed and monitored by two independent methods, and acetic anhydride termination was incorporated to minimize formation of deletion peptides. The homogeneity of the final product, obtained in 18% yield, was assessed by t.l.c., disc electrophoresis, amino-terminal amino acid analysis, and amino acid analyses of acid and enzyme hydrolysates. The purified chicken VIP was shown to be active on gastric acid secretion and on pancreatic blood flow. Previously reported ring closure of the Asp-Asn unit seemed to be at a minimum, owing to the mild basic and acid treatments.

Synthesis of an open-chain asymmmetrical cystine peptide corresponding to the sequence A18-21--B19-26 of bovine insulin by solid phase fragment condensation

An insulin fragment containing residues A 18-21 and B 19-26 linked by the disulfide bond between residues A 20 and B 19 was synthesized. The sequence B 21-26 was assembled on a solid support by the Merrifield technique. The protected fragments A 18-21 and B 19-20 were prepared by conventional methods. After forming the disulfide bridge through cleavage of the S-thiocarbonate derivative of A 18-21 by the thiol peptide B 19-20, the resulting assymmetrical cystine peptide A 18-21--B 19-20 was coupled via the carboxyl group of residue B 20 to the free NH 2-terminal amino group of the protected B 21-26 resin. The product was deprotected, cleaved from the resin, and purified to give the homogenous dodecapeptide A 18-21--B 19-26.