Reactions of Benzene Oxide with Thiols Including Glutathione

详细信息    查看全文

• 作者：Alistair P. Henderson ; Martine L. Barnes ; Christine Bleasdale ; Richard Cameron ; William Clegg ; Sarah L. Heath ; Andrew B. Lindstrom ; Stephen M. Rappaport ; Suramya Waidyanatha ; William P. Watson ; and Be
• 刊名：Chemical Research in Toxicology
• 出版年：2005
• 出版时间：February 2005
• 年：2005
• 卷：18
• 期：2
• 页码：265 - 270
• 全文大小：124K
• 年卷期：v.18,no.2(February 2005)
• ISSN：1520-5010

文摘

S-Phenylmercapturic acid is a minor metabolite of benzene used as a biomarker for humanbenzene exposures. The reaction of intracellular glutathione with benzene oxide-oxepin, theinitial metabolite of benzene, is presumed to give 1-(S-glutathionyl)-cyclohexa-3,5-dien-2-ol,which undergoes dehydration to S-phenylglutathione, the precursor of S-phenylmercapturicacid. To validate the proposed route to S-phenylglutathione, reactions of benzene oxide-oxepinwith glutathione and other sulfur nucleophiles have been studied. The reaction of benzeneoxide with an excess of aqueous sodium sulfide, followed by acetylation, gave bis-(6-trans-5-acetoxycyclohexa-1,3-dienyl)sulfide, the structure of which was proved by X-ray crystallography.Reactions of benzene oxide-oxepin in a 95:5 (v/v) mixture of phosphate buffer in D₂O with(CD₃)₂SO were monitored by ¹H NMR spectroscopy. In the absence of glutathione, the half-life of benzene oxide-oxepin was ca. 34 min at 25 C and pD 7.0. The half-life was not affectedin the range of 2-15 mM glutathione in the presence and absence of a commercial sample ofhuman glutathione S-transferase (at pH 7.0, 8.0, 8.5, or 10.0). The adduct 1-(S-glutathionyl)-cyclohexa-3,5-diene-2-ol was identified in these reaction mixtures, especially at higher pH, bymass spectrometry and by its acid-catalyzed decomposition to S-phenylglutathione. Incubationof benzene oxide with N-acetyl-L-cysteine at 37 C and pH 10.0 and subsequent massspectrometric analysis of the mixture showed formation of pre-S-phenylmercapturic acid andthe dehydration product, S-phenylmercapturic acid. The data validate the premise that benzeneoxide-oxepin can be captured by glutathione to give (1R,2R)- and/or (1S,2S)-1-(S-glutathionyl)-cyclohexa-3,5-dien-2-ol, which dehydrate to S-phenylglutathione. The capture is a relativelyinefficient process at pH 7 that is accelerated at higher pH. These studies account for theobservation that the metabolism of benzene is dominated by the formation of phenol. Thepathway leading to S-phenylmercapturic acid is necessarily minor on account of the lowefficiency of benzene oxide capture by glutathione at pH 7 vs spontaneous rearrangement tophenol.