Stereoselective oxidation of styrene to styrene oxide in rats as measured by mercapturic acid excretion.

1. Administration of styrene (I) and styrene oxide (II) to rats resulted in the excretion of 2-hydroxymercapturic acids, N-acetyl-S-(1-phenyl-2-hydroxyethyl)cysteine (III) and N-acetyl-S-(2-phenyl-2-hydrosyethyl)cysteine (IV). Each appeared to be a mixture of diastereoisomers. 2. Administration of optically pure styrene oxide resulted in formation of one set of diastereoisomers. Racemic styrene oxide gave equal amounts of diastereoisomers. Thus the opening of the epoxide ring by glutathione S-transferases was stereospecific and the transferases showed no preference for one of the isomers of styrene oxide. 3. After administration of styrene the observed ratio of the diastereoisomers for both hydroxymercapturic acids was about 1:4. This leads to the conclusion that there is a stereoselective oxidation of styrene to styrene oxide, with a preference for the R-isomer.