Use of BOP-Cl in the presence of Boc-amino monothioacids for the thioacylation of imino acid residues.

BOP-Cl was found to be an efficient coupling reagent for the introduction of thiopeptide bonds on imino acid residues (Pro, Sar). Boc-amino monothioacids were coupled at moderate temperature (0 degree C-RT) with fair yields and with retained optical purity. The mechanism of the coupling reaction is discussed.