Spontaneous and enzyme-catalyzed hydrolysis of saturated oxazolinones

The spontaneous and enzyme-catalyzed hydrolyses of a number of saturated oxazolinones have been investigated by following the decrease in ultraviolet absorbance which occurs on ring opening. Rate constants determined for the hydrolyses of saturated oxazolinones indicate the high reactivity of the oxazolinone carbonyl carbon toward nucleophilic attack. Oxazolinones have been shown to be good substrates for a number of hydrolytic enzymes. 2-Phenyloxazolin-5-one and 4,4-dimethyl-2-phenyloxazolin-5-one react rapidly with α-chymotrypsin, trypsin, and papain, forming relatively stable acyl-enzymes. The acylation reaction may be observed directly, providing evidence for the three-step mechanism of hydrolysis and a method for titration of the enzyme active sites. 2-Phenyloxazolin-5-one and p-nitrophenyl hippurate have been compared as substrates for α-chymotrypsin and ox liver carboxylesterase. Kinetic data obtained for the achymotrypsin-catalyzed hydrolysis of DL-4-(p-hydroxybenzyl)-2-phenyloxazolin-5-one provide an estimate of the optical specificity shown in both acylation and deacylation reactions.