4‐(Dimethylamino)pyridine N‐oxide (DMAPO): An Effective Nucleophilic Catalyst in the Peptide Coupling Reaction with 2‐Methyl‐6‐nitrobenzoic Anhydride

Abstract Various carboxamides or peptides were synthesized from the corresponding carboxylic acids and amines or α‐amino acids in high yields by the catalysis of 4‐(dimethylamino)pyridine N ‐oxide (DMAPO) with 2‐methyl‐6‐nitrobenzoic anhydride (MNBA). Because the segment‐coupling reaction of α‐amino acids proceeds through the effective activation of the carboxylic acid moieties with DMAPO in the presence of tertiary amines under mild conditions, undesired racemization was hardly observed in the synthesis of oligopeptides such as Z‐Gly‐Phe‐Val‐OMe, Z‐Phe‐Val‐Ala‐OMe, and Bz‐Val‐Val‐OMe.