Madyastha K M, Raj C Paul
Bio-Organic Section, Department of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, India.
Biochem Biophys Res Commun. 2002 Sep 20;297(2):202-5. doi: 10.1016/s0006-291x(02)02179-4.
R-(+)-Pulegone, a monoterpene ketone, is a potent hepatotoxin. One of the major metabolites of pulegone has been shown to be p-cresol, a glutathione depletor and a known toxin. Allylic hydroxylation of 4-methyl-2-cyclohexenone results in the formation of p-cresol. The present study documents for the first time the involvement of cytochrome P-450 system and the stereochemical preference in this hydroxylation reaction. Incubation of PB-induced rat liver microsomes as well as reconstituted PB-induced cytochrome P-450 system with +/-4-methyl-2-cyclohexenone in the presence of NADPH and O(2) resulted in the formation of 4-hydroxy-4-methyl-2-cyclohexenone and p-cresol. From the assay mixture, the unreacted substrate, viz., 4-methyl-2-cyclohexenone was isolated and purified and its optical rotation was found to be 2.2 (in CHCl(3)). The observed enantiomeric excess in the recovered substrate was further confirmed by circular dichroism (CD) studies. The CD spectrum has a peak at 292nm and a trough at 270nm. The enantiomeric excess in the recovered substrate indicates that the hydroxylation at C-4 position is stereoselective. The significance of these results with respect to pulegone-mediated hepatotoxicity is discussed.
R-(+)-胡薄荷酮，一种单萜酮，是一种强效肝毒素。已证明胡薄荷酮的主要代谢产物之一是对甲酚，一种谷胱甘肽消耗剂和已知毒素。4-甲基-2-环己烯酮的烯丙基羟基化导致对甲酚的形成。本研究首次记录了细胞色素P-450系统的参与以及该羟基化反应中的立体化学偏好。在NADPH和O₂存在下，将PB诱导的大鼠肝微粒体以及重组的PB诱导的细胞色素P-450系统与±4-甲基-2-环己烯酮一起孵育，导致形成4-羟基-4-甲基-2-环己烯酮和对甲酚。从测定混合物中分离并纯化未反应的底物，即4-甲基-2-环己烯酮，发现其旋光度为2.2（在CHCl₃中）。通过圆二色性（CD）研究进一步证实了回收底物中观察到的对映体过量。CD光谱在292nm处有一个峰，在270nm处有一个谷。回收底物中的对映体过量表明C-4位的羟基化是立体选择性的。讨论了这些结果对胡薄荷酮介导的肝毒性的意义。
