Völkel W, Dekant W
Department of Toxicology, University of Würzburg, Versbacherstrasse 9, 97078 Würzburg, Germany.
Chem Res Toxicol. 1998 Sep;11(9):1082-8. doi: 10.1021/tx980084d.
Chlorothioketene has been suggested as a reactive intermediate formed by the cysteine conjugate beta-lyase-mediated cleavage of S-(1,2-dichlorovinyl)-L-cysteine, a minor metabolite of trichloroethene. Halothioketenes are highly reactive, and their intermediate formation may be confirmed by reactions such as cycloadditions and thioacylations of nucleophiles. A precursor of chlorothioketene, S-(1,2-dichlorovinyl)thioacetate, is readly accessible by the reaction of dichloroethyne with thioacetic acid. In presence of base, S-(1,2-dichlorovinyl)thioacetate is cleaved to chlorothioketene. Chlorothioketene is not stable at room temperature and was characterized after transformation to stable products by reaction with compounds such as cyclopentadiene, N,N-diethylamine, and ethanol. In organic solvents, the cleavage of S-(1, 2-dichlorovinyl)thioacetate in the presence of cytosine results in N4-acetylcytosine, N4-(chlorothioacetyl)cytosine, and small amounts of 3-(N4-thioacetyl)cytosine. No reaction products were seen with guanosine, adenosine, and thymidine under identical conditions. When cytosine was reacted with S-(1,2-dichlorovinyl)thioacetate in aqueous solutions, only N4-acetylcytosine was formed. N4-(Chlorothioacetyl)cytosine and 3-(N4-thioacetyl)cytosine were not detected even when using a very sensitive method, derivatization with pentafluorobenzyl bromide and electron capture mass spectrometry with a detection limit of 50 fmol/microliter of injection volume. Aqueous solutions of DNA cleave S-(1, 2-dichlorovinyl)thioacetate to give N4-acetyldeoxycytidine in DNA, but chlorothioketene adducts of deoxynucleosides were also not detected in these experiments. These results confirm the electrophilic reactivity of chlorothioketene toward nucleophilic groups of DNA constituents in inert solvents but also demonstrate that the formation of DNA adducts under physiological conditions likely is not efficient. Therefore, DNA adducts may not represent useful biomarkers of exposure and biochemical effects for trichloroethene.
氯代硫代乙烯酮被认为是由半胱氨酸共轭β-裂解酶介导的三氯乙烯的一种次要代谢产物S-(1,2-二氯乙烯基)-L-半胱氨酸裂解形成的反应中间体。卤代硫代乙烯酮具有高反应活性，其中间体的形成可通过亲核试剂的环加成和硫酰化等反应来证实。氯代硫代乙烯酮的前体S-(1,2-二氯乙烯基)硫代乙酸酯可通过二氯乙炔与硫代乙酸的反应轻松获得。在碱的存在下，S-(1,2-二氯乙烯基)硫代乙酸酯裂解生成氯代硫代乙烯酮。氯代硫代乙烯酮在室温下不稳定，在与环戊二烯、N,N-二乙胺和乙醇等化合物反应转化为稳定产物后进行了表征。在有机溶剂中，S-(1,2-二氯乙烯基)硫代乙酸酯在胞嘧啶存在下裂解生成N4-乙酰胞嘧啶、N4-(氯代硫代乙酰基)胞嘧啶和少量的3-(N4-硫代乙酰基)胞嘧啶。在相同条件下，鸟苷、腺苷和胸苷未观察到反应产物。当胞嘧啶在水溶液中与S-(1,2-二氯乙烯基)硫代乙酸酯反应时，仅形成N4-乙酰胞嘧啶。即使使用非常灵敏的方法，即五氟苄基溴衍生化和检测限为50飞摩尔/微升进样体积的电子捕获质谱法，也未检测到N4-(氯代硫代乙酰基)胞嘧啶和3-(N4-硫代乙酰基)胞嘧啶。DNA水溶液将S-(1,2-二氯乙烯基)硫代乙酸酯裂解，在DNA中生成N4-乙酰脱氧胞苷，但在这些实验中也未检测到脱氧核苷的氯代硫代乙烯酮加合物。这些结果证实了氯代硫代乙烯酮在惰性溶剂中对DNA成分亲核基团的亲电反应活性，但也表明在生理条件下DNA加合物的形成可能效率不高。因此，DNA加合物可能不代表三氯乙烯暴露和生化效应的有用生物标志物。
