Studies on peptides. LXXXVII. Synthesis of an octacosapeptide amide corresponding to the entire amino acid sequence of chicken vasoactive intestinal polypeptide (VIP).

The octacosapeptide amide corresponding to the entire amino acid sequence of chicken VIP was synthesized in a conventional manner, using a new arginine derivative, NG-mesitylene-2-sulfonylarginine, Arg(Mts). Treatment of a fragment, Z(OMe)-Thr-Asp-Asn-Tyr-NHNH2 with methanesulfonic acid or HBr was found to give a product with a low recovery of Asp, after aminopeptidase digestion. Ring closure of the Asp-Asn unit seemed to be responsible for this phenomenon. Deprotection with HF or TFA exhibited definitely less such a tendency. In the final step of the synthesis, all protecting groups, including the Mts group, were removed by HF in the presence of m-cresol and the deprotected peptide was purified by ion-exchange chromatography on CM-cellulose followed by isoelectric focusing in Ampholine pH 9--1. Synthetic peptide exhibited the identical Rf value with that of natural chicken VIP and was active as the natural peptide.