Peptide Weinreb amide derivatives as thioester precursors for native chemical ligation

Peptide Weinreb amide derivatives with an N-substituted mercaptoethyl group are designed as thioester precursors for native chemical ligation. We show that these amides undergo rapid ligation with a cysteinyl peptide under normal NCL conditions to form various Xaa-Cys peptide bonds, including the difficult Val-Cys junction. Facile synthesis of the Weinreb amide linkers allows easy access to this new type of peptide thioester precursor by standard Fmoc solid phase synthesis.