Thioacylating intermediates as metabolites of S-(1,2-dichlorovinyl)-L-cysteine and S-(1,2,2-trichlorovinyl)-L-cysteine formed by cysteine conjugate .beta.-lyase

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Abstract
The bioactivation mechanism of S-(1,2-dichlorovinyl)-L-cysteine (DCVC) and S-(1,2,2-trichlorovinyl)-L-cysteine (TCVC) was studied with cysteine conjugate .beta.-lyase (.beta.-lyase) from Salmonella typhimurium and with the pyridoxal phosphate model N-dodecylpyridoxal bromide (PL-Br) as catalysts and with GC/MS to identify the metabolites formed. PL-Br converted S-2-benzothiazolyl-L-cysteine to 2-mercaptobenzothiazole and S-benzyl-L-cysteine to benzyl mercaptan, demonstrating the ability of PL-Br to serve as a model for .beta.-lyase. PL-Br and bacterial .beta.-lyase converted DCVC to chloroacetic acid and chlorothionoacetic acid and TCVC to dichloroacetic acid. Incubations of PL-Br with the S-conjugates in the presence of diethylamine resulted in the formation of N,N-diethylchlorothioacetamide from DCVC and of N,N-diethyldichlorothioacetamide from TCVC. Attempts to trap the enethiols, which are the expected initial products formed by .beta.-elimination, by reaction with methyl iodide in incubations with the .beta.-lyase model were not successful. The formation of thioacylating agents from the enetiols may contribute to the cytotoxic and mutagenic effects of DCVC and TCVC.