N-Methylated Peptide Synthesis via in situ Generation of Pivaloyl Mixed Anhydrides

N-methylated peptides are crucial for drug development but face synthesis hurdles like low reactivity of conventional coupling reagents and racemization. This study develops a practical method for their synthesis via in situ generation of pivaloyl mixed anhydrides using low-cost pivaloyl anhydride (Piv₂O) as the coupling reagent, without pre-preparing mixed anhydrides and under moderate temperature and base-free condition. The method achieves high yields, good compatibility with diverse amino acids, and excellent racemization suppression. It outperforms traditional methods in synthesizing N-methylated peptides and successfully prepares Cyclosporin A fragments and Ciliatamide B.