Chemical Protein Synthesis by Hydroxylamine-Involved Ligation of Peptides

Chemical protein synthesis by native amide ligation between two unprotected peptides provides an effective protocol. It is well-known that the development of a ligation method that is not limited by the sites of specific amino acids is highly desired. Here, we report an efficient chemoselective ligation between C-terminal peptide thioesters and N-terminal aminoacyl- N -hydroxy peptides in water (pH 8) at room temperature. The ligation reaction undergoes sequential S, O -ester exchange of peptide thioesters with N -hydroxyl of aminoacyl- N -hydroxy peptides providing O -acyl isopeptides and O, N -acyl transfer across a six-membered ring yielding ligated N -hydroxyl peptides. Reduction of N -hydroxyl peptides with zinc in an aqueous medium (pH 3) affords long peptides with native amide bonds. This hydroxylamine-involved ligation (HAL) of peptides was successfully applied to the synthesis of ubiquitin.