Urano Y, Higuchi T, Hirobe M
Faculty of Pharmaceutical Sciences, University of Tokyo, Japan.
Biochem Biophys Res Commun. 1993 Apr 30;192(2):568-74. doi: 10.1006/bbrc.1993.1453.
Aromatic ring hydroxylation of phenolic compounds proceeded selectively in a Cu(2+)-ascorbic acid-O2 system. In contrast to usual oxidation systems, unusual substituent effects were observed: electron-withdrawing groups accelerate and electron-donating groups retard the hydroxylation. Hydroxyl radicals generated by gamma-radiolysis also converted phenols into catechols and hydroquinones. The close resemblance of these two systems led us to presume that the active intermediate in the Cu(2+)-ascorbic acid-O2 system is hydroxyl radical or an equivalent species. The unusual substituent effects were also observed in the hydroxylation of p-substituted phenol by microsomes, a cytochrome P-450-dependent reaction. These results imply that the Cu(2+)-ascorbic acid-O2 system is an effective biomimetic oxidation system.
酚类化合物的芳环羟基化反应在Cu(2+)-抗坏血酸-O2体系中选择性地进行。与通常的氧化体系不同，观察到了异常的取代基效应：吸电子基团加速羟基化反应，而供电子基团则阻碍羟基化反应。由γ-辐射分解产生的羟基自由基也能将酚类转化为儿茶酚和对苯二酚。这两种体系的相似性使我们推测，Cu(2+)-抗坏血酸-O2体系中的活性中间体是羟基自由基或类似的物种。在微粒体对p-取代苯酚的羟基化反应（一种细胞色素P-450依赖的反应）中也观察到了这种异常的取代基效应。这些结果表明，Cu(2+)-抗坏血酸-O2体系是一种有效的仿生氧化体系。
