Finkelstein M B, Dekant W, Anders M W
Department of Pharmacology, University of Rochester, New York 14642, USA.
Chem Res Toxicol. 1996 Jan-Feb;9(1):227-31. doi: 10.1021/tx950142k.
1,1-Dichloroalkene-derived S-(1-chloroalkenyl)-L-cysteine conjugates, but not 1,1-difluoroalkene-derived S-(2,2-dihalo-1,1-difluoroethyl)-L-cysteine conjugates, are mutagenic in the Ames test. Recent studies have showed, however, that bromine-containing, 1,1-difluoroalkene-derived S-(2-bromo-2-halo-1,1-difluoroethyl)-L-cysteine conjugates are mutagenic [Finkelstein, M. B., et al. (1994) Chem. Res. Toxicol. 7, 157-163] and that alpha-thiolactones are formed as reactive intermediates and glyoxylate as a terminal product [Finkelstein, M. B., et al. (1995) J. Am. Chem. Soc. 117, 9590-9591]. The present studies were undertaken to examine the stoichiometry of cysteine conjugate beta-lyase-catalyzed product formation from a panel of bromine-containing and bromine-lacking cysteine S-conjugates and to search for additional metabolites. The cysteine S-conjugates were incubated with rat renal homogenates, and pyruvate:product (glyoxylate, bromide, fluoride, dihaloacetate, trihaloethene) ratios were measured. Pyruvate:glyoxylate ratios for S-(2-bromo-1,1,2-trifluoroethyl)-L-cysteine, S-(2-bromo-2-chloro-1,1-difluoroethyl)-L-cysteine, and S-(2,2-dibromo-1,1-difluoroethyl)-L-cysteine ranged from 1:0.13 to 1:0.16. With S-(2-bromo-2-chloro-1,1-difluoroethyl)-L-cysteine and S-(2-bromo-1,1,2-trifluoroethyl)-L-cysteine, pyruvate:bromide ratios were 1:1, but with the dibrominated conjugate S-(2,2-dibromo-1,1-difluoroethyl)-L-cysteine, the pyruvate:bromide ratio was 1:1.2. All bromine-containing cysteine S-conjugates gave less than complete conversion to fluoride. A search for additional metabolites led to the consideration of 2,2-difluoro-3-halothiiranes as putative intermediates. 2,2-Difluoro-3-halothiiranes may arise by internal displacement of bromide and cyclization of 2-bromo-2-halo-1,1-difluoroethanethiolates, which are beta-elimination products of cysteine S-conjugates. Such halogenated thiiranes may eliminate sulfur to give 1,1-difluoro-2-haloethenes. GC/MS analysis showed that trifluoroethene, 2-chloro-1,1-difluoroethene, and 2-bromo-1,1-difluoroethene were terminal products of S-(2-bromo-1,1,2-trifluoroethyl)-L-cysteine, S-(2-bromo-2-chloro-1,1-difluoroethyl)-L-cysteine, and S-(2,2-dibromo-1,1-difluoroethyl)-L-cysteine, respectively. The bromine-lacking conjugate S-(2-chloro-1,1,2-trifluoroethyl)-L-cysteine did not yield glyoxylate or trifluoroethene as products, but the formation of chlorofluoroacetate was confirmed. The pyruvate:chlorofluoroacetate ratio was 1:0.38, indicating that other products are formed. This is the first report of the stoichiometry of the beta-lyase-catalyzed biotransformation of haloalkene-derived cysteine S-conjugates and of the formation of 2,2-difluoro-3-halothiiranes as reactive intermediates in the biotransformation of bromine-containing cysteine S-conjugates.
1,1 - 二氯烯烃衍生的S - (1 - 氯代烯基)-L - 半胱氨酸共轭物在艾姆斯试验中具有致突变性，而1,1 - 二氟烯烃衍生的S - (2,2 - 二卤 - 1,1 - 二氟乙基)-L - 半胱氨酸共轭物则没有。然而，最近的研究表明，含溴的1,1 - 二氟烯烃衍生的S - (2 - 溴 - 2 - 卤 - 1,1 - 二氟乙基)-L - 半胱氨酸共轭物具有致突变性[芬克尔斯坦，M. B.等人(1994年)《化学研究毒理学》7卷，第157 - 163页]，并且α - 硫内酯作为反应中间体形成，乙醛酸作为终产物[芬克尔斯坦，M. B.等人(1995年)《美国化学会志》117卷，第9590 - 9591页]。本研究旨在研究一系列含溴和不含溴的半胱氨酸S - 共轭物经半胱氨酸共轭物β - 裂解酶催化的产物形成的化学计量关系，并寻找其他代谢产物。将半胱氨酸S - 共轭物与大鼠肾匀浆一起孵育，然后测量丙酮酸:产物(乙醛酸、溴化物、氟化物、二卤乙酸、三卤乙烯)的比例。S - (2 - 溴 - 1,1,2 - 三氟乙基)-L - 半胱氨酸、S - (2 - 溴 - 2 - 氯 - 1,1 - 二氟乙基)-L - 半胱氨酸和S - (2,2 - 二溴 - 1,1 - 二氟乙基)-L - 半胱氨酸的丙酮酸:乙醛酸比例在1:0.13至1:0.16之间。对于S - (2 - 溴 - 2 - 氯 - 1,1 - 二氟乙基)-L - 半胱氨酸和S - (2 - 溴 - 1,1,2 - 三氟乙基)-L - 半胱氨酸，丙酮酸:溴化物比例为1:1，但对于二溴化共轭物S - (2,2 - 二溴 - 1,1 - 二氟乙基)-L - 半胱氨酸，丙酮酸:溴化物比例为1:1.2。所有含溴的半胱氨酸S - 共轭物转化为氟化物的程度均不完全。对其他代谢产物的寻找导致考虑将2,2 - 二氟 - 3 - 卤代硫杂环丙烷作为假定的中间体。2,2 - 二氟 - 3 - 卤代硫杂环丙烷可能通过溴化物的分子内取代和2 - 溴 - 2 - 卤 - 1,1 - 二氟乙硫醇盐的环化反应生成，而2 - 溴 - 2 - 卤 - 1,1 - 二氟乙硫醇盐是半胱氨酸S - 共轭物的β - 消除产物。这种卤代硫杂环丙烷可能消除硫生成1,1 - 二氟 - 2 - 卤代乙烯。气相色谱/质谱分析表明，三氟乙烯、2 - 氯 - 1,1 - 二氟乙烯和2 - 溴 - 1,1 - 二氟乙烯分别是S - (2 - 溴 - 1,1,2 - 三氟乙基)-L - 半胱氨酸、S - (2 - 溴 - 2 - 氯 - 1,1 - 二氟乙基)-L - 半胱氨酸和S - (2,2 - 二溴 - 1,1 - 二氟乙基)-L - 半胱氨酸的终产物。不含溴的共轭物S - (2 - 氯 - 1,1,2 - 三氟乙基)-L - 半胱氨酸不产生乙醛酸或三氟乙烯作为产物，但氯氟乙酸的形成得到了证实。丙酮酸:氯氟乙酸比例为1:0.38，表明还形成了其他产物。这是关于卤代烯烃衍生的半胱氨酸S - 共轭物经β - 裂解酶催化的生物转化的化学计量关系以及在含溴半胱氨酸S - 共轭物的生物转化中作为反应中间体的2,2 - 二氟 - 3 - 卤代硫杂环丙烷形成的首次报道。
