Highly efficient synthesis of sterically hindered peptides containing N-methylated amino acid residues using a novel 1H-benzimidazolium salt

Novel 1H-benzimidazolium type peptide coupling reagent, CMBI, was designed, synthesized, and shown to be efficient in the promotion of the formation o f sterically hindered amide and ester bonds. Its high efficiency was proved by model reaction tests and the successful synthesis of various hindered o ligopeptides and peptide segments containing N-methyl amino acid residues w ith fast reaction speeds, low racemization and excellent yields. A mechanis m for amide bond formation mediated by the reagent was proposed. (C) 2000 E lsevier Science Ltd. All rights reserved.