Asymmetric Synthesis of Unnatural Amino Acid-containing Peptides via Direct Asymmetric Reaction of Peptidyl Compounds

Abstract

Unnatural amino acids and the peptides bearing such units have gathered much attention due to their interesting biological activities and synthetic utility as chiral building blocks for the synthesis of complex molecules. This paper descibes an asymmetric synthesis of unnatural amino acid derivatives and their subsequent application to the preparation of unnatural amino acid-containing peptides. The α-imino carboxylic acid derivatives, which are common substrates for the synthesis of unnatural amino acids, could be readily prepared by MnO₂-mediated oxidation of N-PMP-protected glycine derivatives. This reaction allowed us to synthesize novel derivatives such as α-imino perfluoroalkylesters, imides or thioesters. These compounds are useful for the synthesis of unnatural amino acid derivatives. MnO₂-mediated oxidation was further applied to the synthesis of peptidyl imine. Moreover, a new methodology for the synthesis of unnatural amino acid-containing peptides was developed using the thus obtained imino peptides. This novel approach should be useful for the divergent synthesis of peptides possessing varieties of unnatural amino acid moieties.