酶催化反应是绿色化学领域中的研究热点之一.在常用的酶中,漆酶是一种多铜氧化酶.在此,漆酶被用来研究邻苯二酚的氧化和芳香环开环的自由基过程.实验表明,邻苯二酚的初始氧化产物是一个半醌自由基,再发生分子间加成反应而生成二聚体和三聚体(通过质谱鉴定),和分子内加成而生成可被5, 5-二甲基-1-氧化吡咯啉(DMPO)所捕获的含有支链烷基自由基的呋喃衍生物.后者经核磁共振氢谱(1H-NMR)加以分析.同时,通过17O同位素标记追踪方法,我们发现水直接参与该分子内加成反应,并释放出17O标记的羟基自由基(·17OH).此外,除了3-甲基邻苯二酚和4-甲基邻苯二酚两种类似物,此自由基过程在间苯二酚、对苯二酚、萘二酚、3-硝基邻苯二酚和4-硝基邻苯二酚等底物中均未发生.据此,我们对C4-C5位点的选择性活化与开环的机理展开分析和讨论,并将该机理与邻苯二酚双加氧酶导致的邻苯二酚双氧中间位置和相邻位置的开环过程相比较.这些结果将有益于漆酶的改造和仿生. Enzyme-catalyzed reactions are a prominent field of research in green chemistry. Laccase is a multicopper oxidase, which we used to study the oxidation of catechol. A mechanism for this ring-opening reaction is also proposed. A o-benzosemiquinone radical was the initial nascent product of catechol oxidation during the catalytic reaction. This radical underwent two reaction pathways:(1) formation of an intramolecular adduct, which gave a carbon-centered furan-derived radical trapped by 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO); (2) formation of an intermolecular adduct producing dimeric and trimeric oligomers, as resolved by mass spectrometry. Products of the furan-like intermediate were also characterized by 1H-NMR. Simultaneously, a hydroxyl radical (·OH) originating from the water solvent was identified by 17O-isotope tracing. The kinetics of this radical were also evident with substrates including 3-and 4-methyl catechol, but not with resorcinol and hydroquinone isomers, 3-and 4-nitro catechol, and 2, 3-dihydroxynaphthalene. The mechanism of selective activation and ring-opening at the C4-C5 site is discussed. This reaction is distinct from intra-and extra-diol ringcleavages catalyzed by catechol dioxygenase. These results are meaningful for mimicking laccase catalysis to further protein design
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