Direct on-resin synthesis of peptide-αthiophenylesters for use in native chemical ligation

A peptide-(alpha)thiophenylester is a key reactant in native chemical ligation. Preformation of the peptide-(alpha)thiophenylester could be useful for enhancing the ligation reaction. We report the direct on-resin preparation of preformed peptide-(alpha)thiophenylesters using a simple and efficient method. The peptide-(alpha)thiophenylester reacted extremely rapidly with a Cys-peptide when compared to the peptide-(alpha)thioalkylester.