Synthesis, conformation, and biological activity of the carbohydrate‐free vespulakinin 1

Synthesis of the carbohydrate-free heptadecapeptide corresponding to the amino acid sequence of vespulakinin 1 was achieved by the continuous flow solid phase procedure on 4-hydroxymethyl-phenoxyacetyl-norleucyl derivatized Kieselguhr-supported polydimethylacrylamide resin, as well as by a combination of solid phase and solution syntheses. Preformed Fmoc-amino acid symmetrical anhydrides (Boc derivative for the N-terminal residue) were used for amine acylation in the continuous flow method. Serine and threonine were side chain protected as tert.-butyl ethers and the 4-methoxy-2, 3, 6,-trimethyl-benzenesulfonyl group was used for masking the guanidino function of arginine residues. After cleavage from the resin the final peptide was purified by ion exchange chromatography and characterized by amino acid analysis, high voltage electrophoresis, and RP-HPLC analysis. Alternatively, the protected N-terminal octapeptide, Fmoc-Thr(But)-Ala-Thr(But)-Thr(But)-Arg(Mtr)-Arg-(Mtr)-Arg(Mtr)-Gly-OH was prepared on 4-hydroxymethyl-3-methoxyphenoxyacetyl-norleucyl derivatized Kieselguhr-supported polydimethylacrylamide resin and the C-terminal nonapeptide H-Arg(NO2)-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg-(NO2)-OBzl was synthesized in solution through the fragment condensation method. The two fragments were coupled by the DCC-HOBt procedure and the resulting heptadecapeptide was deblocked and purified. The conformational features of the synthesized peptides are reported. Preliminary pharmacological experiments indicated that carbohydrate-free vespulakinin 1 is more potent than bradykinin in lowering rat blood pressure.