Identification of urinary mercapturic acids formed from acrylate,methacrylate and crotonate in the rat

1. After administration to rats of methyl acrylate (I), methyl methacrylate (II) and methyl crotonate (III), urinary mercapturic acids were isolated and identified as the dicarboxylic acids N-acetyl-S-(2-carboxyethyl)cysteine (IV, R = H), N-acetyl-S-(2-carboxypropyl)cysteine (V, R = H) and N-acetyl-S-(1-methyl-2-carboxyethyl)cysteine (VI, R = H) and for a minor part as their monomethyl esters IV (R = CH₃), V (R = CH₃) and VI (R = CH₃).

2. After a single dose of the acrylates (I), (II) and (III) (0·14mmol/kg), the excretion of the thioethers amounted to 6·6 ± 0·6, 0·0, and 2·0 ± 0·6% dose respectively.

3. After 18?h previous administration of the carboxylesterase inhibitor tri-o-tolyl phosphate (0·34mmol/kg) the excretion of the thioethers amounted to 40·6 ± 2·1, 11·0 ± 3·3, and 16·0 ± 2·0% dose.

4. For methyl acrylate (I) the ratio of the excreted dicarboxylic acid and monomethyl ester was 20:1. After previous administration of tri-o-tolyl phosphate this ratio was 1 : 2.