Cnubben N H, Vervoort J, Veeger C, Rietjens I M
Department of Biochemistry, Agricultural University, Wageningen, The Netherlands.
Chem Biol Interact. 1992 Dec;85(2-3):151-72. doi: 10.1016/0009-2797(92)90059-t.
The in vitro and in vivo metabolism of monofluoroanilines was investigated. Special attention was focused on the regioselectivity of the aromatic hydroxylation by cytochromes P-450 and the mechanism by which this reaction might proceed. The results clearly demonstrate that the in vitro and in vivo regioselectivity of the aromatic hydroxylation by cytochromes P-450 is dependent on the fluoro-substituent pattern of the aromatic aniline-ring. Results from experiments with liver microsomes from differently pretreated rats demonstrate that the observed regioselectivity for the aromatic hydroxylation is not predominantly determined by the active site of the cytochromes P-450. To investigate the underlying reason for the observed regioselectivity, semi-empirical molecular orbital calculations were performed. Outcomes of these calculations show that neither the frontier orbital densities of the LUMO/LUMO + 1 (lowest unoccupied molecular orbital) of the monofluoroanilines nor the spin-densities in their NH. radicals can explain the observed regioselectivities. The frontier orbital densities of the HOMO/HOMO - 1 (highest occupied molecular orbital) of the monofluoroanilines however, qualitatively correlate with the regioselectivity of the aromatic hydroxylation. Based on these results it is concluded that the cytochrome P-450 dependent aromatic hydroxylation of monofluoroanilines does not proceed by hydrogen or electron abstraction from the aniline substrate to give an aniline-NH. radical. The results rather suggest that cytochrome P-450 catalyzed aromatic hydroxylation of monofluoroanilines proceeds by an electrophilic attack of the (FeO)3+ species of cytochrome P-450 on a specific carbon atom of the aromatic aniline-ring.
研究了单氟苯胺的体外和体内代谢。特别关注细胞色素P - 450对芳香族羟基化的区域选择性以及该反应可能的进行机制。结果清楚地表明，细胞色素P - 450对芳香族羟基化的体外和体内区域选择性取决于芳香族苯胺环的氟取代模式。来自不同预处理大鼠肝脏微粒体的实验结果表明，观察到的芳香族羟基化区域选择性并非主要由细胞色素P - 450的活性位点决定。为了研究观察到的区域选择性的潜在原因，进行了半经验分子轨道计算。这些计算结果表明，单氟苯胺的LUMO/LUMO + 1（最低未占分子轨道）的前沿轨道密度及其NH·自由基中的自旋密度均无法解释观察到的区域选择性。然而，单氟苯胺的HOMO/HOMO - 1（最高占据分子轨道）的前沿轨道密度与芳香族羟基化的区域选择性在性质上相关。基于这些结果得出结论，细胞色素P - 450依赖的单氟苯胺芳香族羟基化不是通过从苯胺底物夺取氢或电子生成苯胺 - NH·自由基来进行的。结果反而表明，细胞色素P - 450催化的单氟苯胺芳香族羟基化是通过细胞色素P - 450的(FeO)3+物种对芳香族苯胺环的特定碳原子进行亲电攻击来进行的。
