Metabolites of [3-13C]1,2-dibromo-3-chloropropane in male rats studied by 13C and 1H-13C correlated two-dimensional NMR spectroscopy.

ABSTRACT

Metabolism of 1,2-dibromo-3-chloropropane (DBCP) was examined by direct 13C and 1H-13C correlated two-dimensional NMR spectroscopy of bile and urine of male albino rats treated intraperitoneally with [3-13C]DBCP at 81 mg/kg. The 3-13C label was introduced at 99% enrichment by coupling [13C]paraformaldehyde with vinyllithium to give [1-13C]allyl alcohol which was converted to allyl chloride with carbon tetrachloride/triphenylphosphine and then brominated. Fifteen 13C NMR signals were observed for biliary metabolites and twelve for urinary metabolites. Nine of the biliary metabolite 13C NMR signals were very similar or identical to those for nine urinary metabolites. The DBCP-derived moieties of five metabolites were identified by comparison of their 13C NMR chemical shifts, 13C multiplicities [obtained via the distortionless enhancement by polarization transfer (DEPT) pulse sequence], and chemical shifts of the directly-attached protons (obtained via two-dimensional NMR) with those of authentic standards. They were E- and Z-RSCH2CH = 13CHCl, RSCH2CHOH13CH2Cl, RSCH2CHOH13CH2OH and RS13CH2CHOHCH2OH, where R is probably glutathionyl in bile and N-acetylcysteinyl in urine. The mechanism proposed for formation of both the E- and Z-isomers of RSCH2CH = 13CHCl involves radical-initiated dehydrobromination followed by reaction of the intermediate allylic bromides with glutathione (GSH). The RSCH2CHOHCH2Cl conjugate may arise from direct GSH conjugation and hydrolysis of the secondary bromine via a thiiranium ion intermediate. The proposed origin of the RSCH2CHOHCH2OH conjugate labeled at either carbon-1 or carbon-3 is oxidation of DBCP at the bromomethyl or chloromethyl substituent, respectively, followed by two spontaneous dehydrohalogenations to give the highly reactive 2-bromopropenal, and addition of GSH followed by reduction of the aldehyde functionality. An alternative mechanism for the formation of the RSCH2CHOHCH2Cl and RSCH2CHOHCH2OH derivatives involves carbon-2 oxidation to give 1-bromo-3-chloroacetone followed by reaction with GSH and reduction of the ketone functionality with or without hydrolysis of the chloro substituent. 2-Bromopropenal, 1-bromo-3-chloroacetone, or GSH conjugates derived from these intermediates may be involved in the male reproductive toxicity, nephrotoxicity and genotoxicity of DBCP.