Amide-forming chemical ligation via O -acyl hydroxamic acids

Significance Methods for the chemoselective formation of peptide bonds in water generally leverage the exceptional reactivity of thiol nucleophiles. Here, we demonstrate that hydroxamic acids—incorporated into the side chain of asparagine or aspartic acid—can be leveraged analogously. N -terminal hydroxy-asparagine-peptides react with peptide- α thioesters to form “ O -acyl hydroxamic acid isopeptides," which rearrange to peptide bonds via a facile O , N -acyl shift. The hydroxy-asparagine residue can be converted to either aspartic acid or asparagine, to furnish amide-linked ligation products comprising entirely canonical residues. Taken together, these observations form the basis of a strategy for peptide ligation that circumvents the requirement for Xaa-Cys ligation “sites.”