Bolton J L, Comeau E, Vukomanovic V
Department of Chemistry, Queen's University, Kingston, Ontario, Canada.
Chem Biol Interact. 1995 Apr 14;95(3):279-90. doi: 10.1016/0009-2797(94)03566-q.
The effects of para-alkyl substituents on both the cytochrome P450-catalyzed oxidation of phenols to quinone methides (QMs; 4-methylene-2,5-cyclohexadien-1-ones), and on the rates of nucleophilic additions to the QMs were investigated. The derivatives of 4-alkyl-2-methoxyphenol studied were 4-methyl (creosol), 4-ethyl, 4-propyl, 4-isopropyl, and 4-allyl (eugenol). The relative reactivities of QMs derived from these phenols with water were 4-methyl > 4-ethyl = 4-propyl > 4-isopropyl > 4-allyl. These variations in rate were rationalized by differences in stabilization of positive charge density at the site of nucleophilic attack. In particular, saturation of the vinyl substituent on eugenol-QM increases the solvolysis rate 100-fold. This effect is presumably due to the loss of the contribution of an additional aromatic resonance structure to the overall resonance hybrid of the QM from 2-methoxy-4-propylphenol. Finally, the kinetic results show that there is a 472-fold difference in reactivity within this series of QMs. The QM glutathione conjugates were synthesized and characterized by 1H-NMR and electrospray mass spectrometry and a HPLC assay was developed to quantify QM formation in rat liver microsomes. The general trend is increasing alkyl substitution at the para position results in more QM; however, in contrast to the large range of reactivities of the QMs observed in the kinetic experiments, the amounts of P450-derived QM GSH adducts varied only by a factor of 3. In particular, similar amounts of the QMs from eugenol and 2-methoxy-4-propylphenol were produced which suggests that the lack of reported hepatotoxicity for the latter phenol in mice depleted of GSH, may be due to the extreme reactivity of 4-propyl-QM that would be rapidly detoxified by hydrolysis. These data suggest that there may be a threshold cytotoxicity level for QMs related to their reactivity which may affect the relative toxicities of 4-alkyl-2-methoxyphenols.
研究了对位烷基取代基对细胞色素P450催化酚类氧化为醌甲基化物（QMs；4-亚甲基-2,5-环己二烯-1-酮）的影响，以及对亲核试剂加成到QMs的速率的影响。所研究的4-烷基-2-甲氧基苯酚衍生物有4-甲基（甲酚）、4-乙基、4-丙基、4-异丙基和4-烯丙基（丁香酚）。这些酚类衍生的QMs与水的相对反应活性为4-甲基＞4-乙基 = 4-丙基＞4-异丙基＞4-烯丙基。速率的这些变化通过亲核攻击位点处正电荷密度稳定化的差异得到合理解释。特别地，丁香酚-QM上乙烯基取代基的饱和使溶剂解速率增加100倍。这种效应可能是由于额外的芳香族共振结构对2-甲氧基-4-丙基苯酚QM的整体共振杂化体的贡献丧失。最后，动力学结果表明在这一系列QMs中反应活性存在472倍的差异。合成了QM谷胱甘肽缀合物，并通过1H-NMR和电喷雾质谱进行表征，还开发了一种HPLC测定法来定量大鼠肝微粒体中QM的形成。一般趋势是对位烷基取代增加会导致更多的QM；然而，与动力学实验中观察到的QMs的大范围反应活性相反，P450衍生的QM谷胱甘肽加合物的量仅相差3倍。特别地，丁香酚和2-甲氧基-4-丙基苯酚产生的QM量相似，这表明在缺乏谷胱甘肽的小鼠中，后一种酚未报告肝毒性，可能是由于4-丙基-QM的极端反应活性会通过水解迅速解毒。这些数据表明，对于QMs可能存在与它们的反应活性相关的细胞毒性阈值水平，这可能会影响4-烷基-2-甲氧基苯酚的相对毒性。
