We introduce a new potent inhibitor, N-[2, 2-dimethyl-3-(N-(4-cyanobenzoyl) amino) nonanoyl]-l-phenylalanine ethyl ester (3), which preferentially inhibits serine proteases belonging to a chymotrypsin superfamily. This inhibitor, despite consisting of a stable ethyl ester structure, showed strong inhibitory activities toward bovine α-chymotrypsin, human cathepsin G, and porcine elastase by acting as an acylating agent. The calculated ...