Ynamide-Mediated Peptide Bond Formation: Mechanistic Study and Synthetic Applications

Ynamides, a class of novel coupling reagents for peptide synthesis, facilitated peptide bond formation in a one-pot, two-step manner with α-acyloxyenamide active esters of amino acids as stable intermediates. Ynamide-mediated peptide synthesis proceeded by a reaction mechanism that is completely different from that of conventional coupling reagents and exhibited superiority in addressing the issue of racemization/epimerization during peptide bond formation. Herein, we present a systematic mechanistic analysis, including kinetics and Brønsted-type structure–reactivity studies and density functional theory calculations, providing unprecedented mechanistic insight into ynamide-mediated peptide bond formation. Based on these mechanistic studies, significant improvements were made, and the applicability of ynamide-mediated peptide bond formation was successfully expanded to peptide fragment condensation, head-to-tail cyclization and solid-phase peptide synthesis.