van der Aar E M, de Groot M J, Bouwman T, Bijloo G J, Commandeur J N, Vermeulen N P
Leiden/Amsterdam Center for Drug Research, Department of Pharmacochemistry, Vrije Universiteit, Amsterdam, The Netherlands.
Chem Res Toxicol. 1997 Apr;10(4):439-49. doi: 10.1021/tx960137w.
In the present study, eleven 4-substituted 1-chloro-2-nitrobenzenes were tested for their GSH conjugation capacity when catalyzed by base or rat glutathione S-transferase (GST) 4-4. Kinetic parameters (ks and K(m), kcat, and kcat/K(m)) were determined and subsequently used for the description of structure-activity relationships (SAR's). For this purpose, eight physicochemical parameters (electronic, steric, and lipophilic) of the substituents and five computer-calculated parameters of the substrates (charge distributions and several energy values) were used in regression analyses with the kinetic parameters. The obtained SAR's are compared with corresponding SAR's for the GSH conjugation of 2-substituted 1-chloro-4-nitrobenzenes, previously determined [Van der Aar et al. (1996) Chem. Res. Toxicol. 9, 527-534]. The kinetic parameters of the 4-substituted 1-chloro-2-nitrobenzenes correlated well with the Hammett sigma p- constant; the Hammett sigma p constant corrected for "through resonance", while the corresponding kinetic parameters of the 2-substituted 1-chloro-4-nitrobenzenes did not. The base- and GST 4-4-catalyzed GSH conjugation reactions of 2-substituted 1-chloro-4-nitrobenzenes depend to a different extent on the electronic properties of the ortho substituents, suggesting the involvement of different rate-limiting transition states. The base- and GST 4-4-catalyzed conjugation of 4-substituted 1-chloro-2-nitrobenzenes, however, showed a similar dependence on the electronic properties of the para substituents, indicating that these substrates are conjugated to GSH via a similar transition state. Multiple regression analyses revealed that, besides electronic interactions, also steric and lipophilic restrictions appeared to play an important role in the GST 4-4-catalyzed GSH conjugation of 4-substituted 1-chloro-2-nitrobenzenes. Finally, the 4-substituted 1-chloro-2-nitrobenzenes were also used to extend the previously described substrate model for GST 4-4 [De Groot et al. (1995) Chem. Res. Toxicol. 8, 649-658], by which a specific steric restriction of substrates for GST 4-4 became clear.
在本研究中，测试了11种4-取代的1-氯-2-硝基苯在碱或大鼠谷胱甘肽S-转移酶（GST）4-4催化下的谷胱甘肽结合能力。测定了动力学参数（ks和K(m)、kcat以及kcat/K(m)），随后用于描述构效关系（SAR）。为此，在与动力学参数的回归分析中使用了取代基的8个物理化学参数（电子、空间和脂溶性）以及底物的5个计算机计算参数（电荷分布和几个能量值）。将得到的SAR与先前测定的2-取代的1-氯-4-硝基苯谷胱甘肽结合的相应SAR进行比较[Van der Aar等人（1996年），《化学研究毒理学》9，527 - 534]。4-取代的1-氯-2-硝基苯的动力学参数与哈米特σp常数相关性良好；哈米特σp常数经“通过共振”校正，而2-取代的1-氯-4-硝基苯的相应动力学参数则不然。2-取代的1-氯-4-硝基苯的碱催化和GST 4-4催化的谷胱甘肽结合反应在不同程度上取决于邻位取代基的电子性质，这表明涉及不同的限速过渡态。然而，4-取代的1-氯-2-硝基苯的碱催化和GST 4-4催化的结合对对位取代基的电子性质表现出相似的依赖性，表明这些底物通过相似的过渡态与谷胱甘肽结合。多元回归分析表明，除电子相互作用外，空间和脂溶性限制在4-取代的1-氯-2-硝基苯的GST 4-4催化的谷胱甘肽结合中似乎也起重要作用。最后，4-取代的1-氯-2-硝基苯还用于扩展先前描述的GST 4-4底物模型[De Groot等人（1995年），《化学研究毒理学》8，649 - 658]，由此GST 4-4底物的特定空间限制变得清晰。
