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 of sterically hindered amide and ester bonds. Its high efficiency was proved by model reaction tests and the successful synthesis of various hindered oligopeptides and peptide segments containing N-methyl amino acid residues with fast reaction speeds, low racemization and excellent yields. A mechanism for amide bond formation mediated by the reagent was proposed.