Reactivity of cysteine S-conjugate sulfoxides: formation of S-[1-chloro-2-(S-glutathionyl)vinyl]-L-cysteine sulfoxide by the reaction of S-(1,2-dichlorovinyl)-L-cysteine sulfoxide with glutathione.

S-(1,2-Dichlorovinyl)-L-cysteine (DCVC) sulfoxide, a putative metabolite of the toxic cysteine S-conjugate DCVC, was synthesized by the reaction of DCVC with H2O2 and characterized by fast atom bombardment mass spectrometry (FAB-MS) and proton nuclear magnetic resonance spectroscopy. DCVC sulfoxide was stable when kept at room temperature overnight in phosphate buffer (pH 6.8-7.8) or when heated in phosphate buffer (pH 7.2 or 7.6) or H2O (pH 3.5 or 10.5) for 20 min at 37 degrees C. However, in the presence of glutathione (GSH), DCVC sulfoxide was readily converted to S-[1-chloro-2-(S-glutathionyl)vinyl]-L-cysteine sulfoxide (I), a product formed by the Michael addition of GSH to DCVC sulfoxide followed by the loss of HCl. Evidence for the mechanism of this reaction was obtained by the finding that DCVC, which cannot act as a Michael acceptor, did not react with GSH under conditions similar to those used with DCVC sulfoxide. When the reaction of DCVC sulfoxide with GSH was carried out at room temperature and pH 7.4, formation of I was complete at 5 min, but when the reaction was carried out for 2 h at pH 6.0 or 4.4 at 37 degrees C, product formation was nearly 37 or 3% of that formed at pH 7.4, respectively; product formation did not increase when the reaction was carried out at pH 8.5. When DCVC sulfoxide (100 mg/kg) was administered to rats, hepatic and renal reduced nonprotein thiol concentrations were decreased at 1 h to 74 and 27% of that in control rats, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)