Metabolism of 1-chloro-2-methylpropene. Evidence for reactive chloroaldehyde intermediates

Recent metabolism and disposition studies of 1-chloro-2-methylpropene (dimethylvinyl chloride) revealed cysteine and N-acetylcysteine conjugates of 3-chloro-2-methylpropenoic acid as the major metabolites. In the present studies we have investigated various steps in the metabolic pathway to determine which step was responsible for the observed trans (E)-stereochemistry of these metabolites. In vitro incubation studies of dimethylvinyl chloride with rat liver microsomes indicated cytochrome P-450-catalyzed aliphatic hydroxylation to be only stereoselective. Both (E)- and (Z)-3-chloro-2-methylpropenols formed in an identical ratio of 2:1 in incubations with microsomes from untreated male and female rats and phenobarbital-treated male rats. No alcohol formation was observed in incubations using microsomes from beta-naphthoflavone-treated male rats. Investigation of the subsequent conjugation reactions of sulfur nucleophiles with haloenoic carbonyl compounds showed that both (E)- and (Z)-3-chloro-2-methylpropenals reacted rapidly with N-acetylcysteine, the E-adduct being the sole product in either case. In contrast, the Michael reaction of the corresponding acids with N-acetylcysteine was very sluggish. Also, whereas the E-acid yielded exclusively the corresponding E-adduct, the Z-isomer afforded both Z- and E-conjugates in the ratio of 3:4. Glutathione S-transferases had poor activity towards conjugation of glutathione with these acids. Formation of only an E-glutathione conjugate could be observed from either the E- or Z-acid in these enzymatic reactions. Direct Michael reaction of glutathione with (E)-3-bromo-2-methylpropenoic acid, used in chemical synthesis of the conjugates, yielded both the E- and Z-adducts in the ratio of 95:5.(ABSTRACT TRUNCATED AT 250 WORDS)