Synthesis of human GLP-1 (7-36) by chemoselective alpha-ketoacid-hydroxylamine peptide ligation of unprotected fragments

The synthesis of the bioactive form of human glucagon-like peptide, GLP-1 (7-36), by the chemoselective ligation of two unprotected fragments, a C-terminal peptide alpha-ketoacid with an N-terminal peptide hydroxylamine, is reported. No reagents are required for the ligation and no byproducts are produced. Unprotected glutamic acid, histidine, arginine, lysine, serine, and tyrosine residues do not interfere with the ligation; no side products arising from undesired reactions of the side chains are detected. This synthesis is the first reported example of the application of the alpha-ketoacid-hydroxylamine amide ligation to the synthesis of a complex, unprotected peptide. Its success underscores the potential broad utility of this amide ligation for the synthesis of complex peptides and related targets.