A number of esters of p-guanidinobenzoic acid have been synthesized which contain a glycolyl peptide as the departing group. In the case of several enzymes such as trypsin and plasma kallikrein, depsipeptides were obtained which were considerably more reactive than the ethyl ester in inactivation of the protease by acyl-enzyme formation; the depsipeptide possessing-CH2CO-Phe-NH2 as a leaving group displayed the highest reactivity. They ...