Aromatic hydroxylations by flavins: evidence on direct attack of phenylalanine by flavin radical species.
作者:Humphrey I.X. Mager、Shiao-Chun Tu
DOI:10.1016/s0040-4020(01)80687-6
日期:1994.5
the protonated form of a flavinoxy radical 3a,b, a product of a homolysis of the OO bond in a dihydroflavin hydroperoxide. As an alternative to the homolysis mentioned, the one-electron oxidation of 1 provides the principle to develop a new hydroxylating model system that does not require a dihydroflavin hydroperoxide as a starting compound. Using phenylalanine as a test substrate, the anaerobic formation
在0.05-12.0 N的酸性溶液中,相应的黄酮阳离子4自发地产生了5-乙基-3-甲基lumlavlavosemiquinone 5(和/或5H +)。将温度从20°C升高至50°C,可显着提高反应速率,而收率5(5H +)则无明显变化。的自发单电子还原4需要具有的单电子氧化偶合另一黄素如5-乙基-4-一个羟基-3-甲基-4-一个,5- dihydroflavin pseudobase 1。后者与4处于平衡状态,可以被氧化生成瞬态5-乙基-4一-羟基-3- methyllumiflavin自由基2。这是黄烷氧基自由基3a ,b的质子化形式,是二氢黄素氢过氧化物中O = O键均质化的产物。作为提到的均质方法的替代方法,单电子氧化1提供了开发新的羟基化模型系统的原理,该系统不需要二氢黄素氢过氧化物作为起始化合物。使用苯丙氨酸作为测试基板,所述厌氧酪氨酸的形成及其ö -和米建立了-羟基苯丙氨酸异