The carbonylhydrazone pseudopeptide link via quinonic oxidation of the peptide amino terminus

Oxidation of the amino terminus in α-amino acid derivatives using 3,5-di-tert-butyl-1,2-quinone generally failed to give the corresponding ketone, and cyclic compounds due to the nucleophilic attack of the phenol hydroxyl in the intermediate 2-aminophenol were recovered. The expected ketone was obtained by using 2,6-di-tert-butyl-1,4-quinone, and the condensation of the ketone and a peptide hydrazide gave the pseudopeptide carbonylhydrazone link.