Synthesis of the New Dipeptide Isoleucylvaline by an Improvement of Methods applied to Aliphatic Amino-acids

Abstract

ALTHOUGH widely applied, the use of methyl or ethyl groups in carboxyl blocking during peptide synthesis sometimes suffers from the subsequent need for hydrolytic cleavage of these esters. In avoiding hydrolysis, the reduction of various blocking groups has been recommended. Among these, benzyl (Bz) might be removed at the same time as the N-p-toluenesulphonyl (Tos) used in blocking amino groups. Since peptide derivatives with these blocking groups crystallize readily, they serve effectively as intermediates in the synthesis of aliphatic peptides. Unfortunately, however, the effective detosyla-tion by sodium–liquid ammonia reduction removes the benzyl group but slowly and consequently gives a low yield of free peptide.