Recent development of peptide coupling reagents in organic synthesis

Abstract

In recent years, peptide coupling reactions have been significantly advanced in accord with the development of new peptide coupling reagents in organic synthesis. Even though a number of valuable reviews have been published in this area, the development of new peptide coupling reagents has been steadily accelerated in the past few years. Moreover, tremendously expanded applications have been possible to new and broad synthetic challenges. This report focuses on the major advances in coupling reagents that have had a great impact in the field. Among many, coupling reagents responsible for the formation of azide, mixed anhydride, and acid halide intermediates have gained substantial popularity in peptide coupling reactions. DCC as a peptide-coupling reagent has particularly attracted organic chemists in their synthesis of complex molecules. Moreover, the development of onium-type coupling reagents has made the incorporation of non-coded or sterically hindered amino acids including N-methylated and a,a-dialkylated amino acids smoothly into the corresponding peptides possible. In a typical peptide coupling reaction, the carboxylic acid moiety of the amino acid I is first activated by an appropriate peptide coupling reagent, and then reacted with the amine moiety of the amino acid II to produce a desired peptide as illustrated in Scheme 1.