A new method for the selective synthesis of unsymmetrical cystine peptides

A convenient method for the synthesis of unsymmetrical cystine peptides is described, which is based on the conversion of one cysteine component to the corresponding sulfenohydrazide by reaction with azodicarboxylic acid derivatives. Following the isolation and characterization of this S-activated intermediate, its thiolysis via the second cysteine component leads to the desired disulfide bridging.