Zhang T L, Wang L, Hashmi M, Anders M W, Thorpe C, Ridge D P
Department of Chemistry and Biochemistry, University of Delaware, Newark 19716, USA.
Chem Res Toxicol. 1995 Oct-Nov;8(7):907-10. doi: 10.1021/tx00049a002.
The cytotoxicity of chloroalkene-derived cysteine S-conjugates is thought to be associated with the formation of alpha-chloroenethiolates and thioketenes as reactive intermediates. Recent studies indicate that the formation of 1,2-dichloroethenethiolate, which may give rise to chlorothioketene, is a key step in the bioactivation of 5,6-dichloro-4-thia-5-hexenoic acid (Fitzsimmons et al. (1995) Biochemistry 34, 4276-4286). We report here the use of Fourier-transform ion cyclotron resonance mass spectrometry to provide the first direct evidence for the formation of alpha-chloroenethiolate and thioketene species from a cytotoxic 4-thiaalkanoate. The bioactivation of 5,6-dichloro-4-thia-5-hexenoic acid involves conversion to the corresponding CoA thioester 5,6-dichloro-4-thia-5-hexenoyl-CoA and subsequent processing by the fatty acid beta-oxidation pathway. It has been proposed that the bioactivation of 5,6-dichloro-4-thia-5-hexenoyl-CoA involves loss of 1,2-dichloroethenethiolate, followed by loss of chloride to form chlorothioketene. 1,2-Dichloroethenethiolate and related alpha-chloroalkenethiolates have not been observed directly in aqueous solution. Fourier-transform ion cyclotron resonance mass spectrometric experiments show that S-propyl 5,6-dichloro-4-thia-5-hexenethioate reacts in the gas phase with base (hydroxide ion) to release 1,2-dichloroethenethiolate, which is observed directly in the mass spectrum of the products of the gas-phase reaction. Furthermore, the elimination of chloride from 1,2-dichloroethenethiolate on collision-induced decomposition is facile and provides evidence for chlorothioketene formation. Preliminary evidence for the formation of 1,2-dichloroethenethiolate and chlorothioketene from S-(1,2-dichlorovinyl)-N-acetyl-L-cysteine methyl ester was also obtained. These observations support the intermediacy of alpha-chloroenethiolates and chlorothioketenes in the bioactivation of cytotoxic, chloroalkene-derived 4-thiaalkanoates and cysteine S-conjugates and demonstrate the utility of Fourier-transform ion cyclotron mass spectrometry in studying the formation of reactive intermediates.
氯代烯烃衍生的半胱氨酸S-共轭物的细胞毒性被认为与作为反应中间体的α-氯代乙烯硫醇盐和硫代烯酮的形成有关。最近的研究表明，可能产生氯代硫代烯酮的1,2-二氯乙烯硫醇盐的形成是5,6-二氯-4-硫杂-5-己烯酸生物活化的关键步骤（菲茨西蒙斯等人（1995年）《生物化学》34卷，4276 - 4286页）。我们在此报告使用傅里叶变换离子回旋共振质谱法，为从一种具有细胞毒性的4-硫杂链烷酸酯形成α-氯代乙烯硫醇盐和硫代烯酮物种提供了首个直接证据。5,6-二氯-4-硫杂-5-己烯酸的生物活化涉及转化为相应的辅酶A硫酯5,6-二氯-4-硫杂-5-己烯酰辅酶A，随后通过脂肪酸β-氧化途径进行处理。有人提出，5,6-二氯-4-硫杂-5-己烯酰辅酶A的生物活化涉及1,2-二氯乙烯硫醇盐的损失，随后氯的损失形成氯代硫代烯酮。在水溶液中尚未直接观察到1,2-二氯乙烯硫醇盐和相关的α-氯代链烯硫醇盐。傅里叶变换离子回旋共振质谱实验表明，S-丙基5,6-二氯-4-硫杂-5-己烯硫代酸酯在气相中与碱（氢氧根离子）反应释放出1,2-二氯乙烯硫醇盐，这在气相反应产物的质谱中直接观察到。此外，1,2-二氯乙烯硫醇盐在碰撞诱导分解时氯的消除很容易，为氯代硫代烯酮的形成提供了证据。还获得了关于从S-(1,2-二氯乙烯基)-N-乙酰-L-半胱氨酸甲酯形成1,2-二氯乙烯硫醇盐和氯代硫代烯酮的初步证据。这些观察结果支持α-氯代乙烯硫醇盐和氯代硫代烯酮在具有细胞毒性的氯代烯烃衍生的4-硫杂链烷酸酯和半胱氨酸S-共轭物生物活化过程中的中间体作用，并证明了傅里叶变换离子回旋共振质谱在研究反应中间体形成方面的实用性。
