Phenyl esters of 2-benzoylbenzoates were determined to be inhibitors of the serine protease enzymes chymotrypsin and thrombin. Thus, p-guanidinophenyl 2-benzoylbenzoate (1b) inhibited thrombin while the corresponding p-nitrophenyl ester (1a) inhibited chymotrypsin activity. Other p-nitrophenyl esters were prepared that display activity as chymotrypsin inhibitors, three having methoxy group substitution on the benzoyl ring: 2-methoxy (2a), 2, ...