Fmoc-D-Lys(Boc)-Opfp

The present work reports the synthesis of a plant-originated cyclooctapeptide--psammosilenin A 8--by cyclization of linear peptide fragment phe-pro-phe-phe-ala-pro-leu-pro-Opfp which was prepared by coupling of tetrapeptide units Boc-phe-pro-phe-phe-OH and ala-pro-leu-pro-OMe followed by proper deprotection of terminal groups and activation of the acid functionality. During synthesis, dicyclohexylcarbodiimide (DCC) and N,N-diisopropylcarbodiimide (DIPC) were used as the coupling agents and N-methylmorpholine (NMM)/triethylamine (TEA) were used as bases. Structure of the synthesized peptide was elucidated by spectral as well as elemental data. The newly synthesized peptide was subjected to biological screening and found to possess potent cytotoxic activity against DLA and EAC cell lines with IC(50) value of 7.93 and 17.06 microM, respectively. Furthermore, good anthelmintic activity against earthworms M. konkanensis and Eudrilus species at 1 and 2 mg/mL was also observed for the synthesized cyclic peptide. Studies indicated that N-methylmorpholine was a more useful base for cyclization of linear peptide unit in comparison to pyridine.

Huwentoxin-I, a neurotoxic peptide from the spiderSelenocosmia huwena, was synthesized by solid-phase method with Fluorenylmethoxycarbonyl amino acid pentafluorophenyl esters (Fmoc-AA-OPfp). The carboxyl and the hydroxy groups were protected by tBu; the side chains of Lys and His were protected by Boc; the guanidine group of Arg was protected by Mtr and the mercaptan group of Cys was protected by Trt. The solid-phase carrier was ethylene diamine-polyethylene-polystyrene (DEA-PEG-PS) resin. The synthetic peptide was cleaved from the resin and deprotected by a 90 % TFA solution containing 5 % thioanisole, 3% ethanedithiol and 2 % anisole. The product was reduced with DTT and then incubated with GSSG and GSH to form the correct disulfide bond linkages. The synthetic peptide was purified by HPLC and then characterized by amino acid composition and sequence analysis, peptide mapping and NMR. The biological activity of the synthetic product was tested by electrophysiological method using the isolated mouse phrenic nerve diaphragm preparation. The results indicated that the synthetic huwentoxin-I has the same chemical and conformational structure and biological activity as those of the native huwentoxin-I from the spider.

Since bioconjugates may play an important role as therapeutics in the future, the development of new and effective conjugation strategies is necessary. For the attachment of peptide-like molecules to carriers, there are two main coupling methods involving amide or disulfide bonds. Conjugation through an amide bond can be achieved in several well-defined ways known from peptide chemistry. However, the formation of disulfide bridges between cysteine-containing peptides and carrier molecules still has some problems. In this paper, we describe a novel approach in which the carrier polypeptide is modified by 3-nitro-2-pyridinesulfenyl (Npys)-protected cysteine and this derivative has been applied for conjugation of Cys-containing epitope peptides with poly(L-lysine)-based branched polypeptides. Considering the stability of Npys group in the presence of pentafluorophenol, Boc-Cys(Npys)-OPfp dervivative was selected for introduction to the N-terminal of branches of polypeptides backbone. The branches of the polymers were built up from oligo(DL-alanine) (poly[Lys(DL-Ala(m))], AK) and elongated by an optically active amino acid [poly[Lys(X(i)-DL-Ala(m))], XAK]. We found that the nature of X (Glu, Ser, Thr) has great influence on the incorporation of the protected cysteine residue. Herpes simplex virus and adenovirus epitope peptides were conjugated to Boc-Cys(Npys)-modified polypeptides. Results indicate that the incorporation of epitope peptides depends on the number of Npys group on the polymers as well as on the presence/absence of Boc-protecting group on the Cys residue. This new class of Cys(Npys)-derivatized branched polypeptides is stable for a couple of months and suitable for effective preparation of epitope peptide conjugates possessing increased water solubility.