OXAZOLINONE INTERMEDIATES IN HYDROLYSIS OF ACTIVATED N-ACYLAMINO ACID ESTERS . RELEVANCE OF OXAZOLINONES TO MECHANISM OF ACTION OF SERINE PROTEINASES

The alkaline hydrolysis of p-nitrophenyl hippurate occurs in two steps. In the first step, which is subject to general base catalysis, p-nitrophenol is released and 2-phenyloxazolin-5-one is formed. Subsequent hydrolysis of this oxazolinone yields hippuric acid. The kinetics of hydrolysis of 16 esters of N-acylamino acids have been investigated to determine the generality of the oxazolinone mechanism, p-Nitrophenyl esters of formyl-, acetyl-, and cinnamoylglycine yield oxazolinone intermediates, whereas benzyloxycarbonylglycine p-nitrophenyl ester does not. Oxazolinone intermediates are formed from a number of activated esters of hippuric acid but not from stable esters such as methyl hippurate. The deacylation of hippuryl-chymotrypsin has been investigated under conditions where 2-phenyloxazolin-5-one could be observed if it were formed. Since no formation of oxazolinone is observed, hippuryl-chymotrypsin behaves as a stable, rather than as an activated, ester of an N-acylamino acid. The reaction of p-nitrophenyl hippurate with imidazole in aqueous solution yields hippurylimidazole rather than 2-phenyloxazolin-5-one. © 1969, American Chemical Society. All rights reserved.