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首页> 外文期刊>Chemistry: A European journal >From a Theoretical Concept to Biochemical Reactions:Strain-Induced Bond Localization(SIBL)in Oxidation of Vitamin E
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From a Theoretical Concept to Biochemical Reactions:Strain-Induced Bond Localization(SIBL)in Oxidation of Vitamin E

机译：从理论概念到生化反应：维生素E氧化中的应变诱导键定位（SIBL）

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摘要

The regioselectivity of the oxidation of a-tocopherol(the main component of vitamin E)to an ortho-quinone methide(oQM)has been explained in the literature mostly by the ill-defined term "Mills-Nixon effect".In this paper we describe the preparation of eleven a-tocopherol derivatives,different from each other by the sum of annulation angles,but keeping the electronic factors unchanged.These compounds underwent Ag2O oxidation,forming two isomeric oQMs that were trapped by vinylmethyl ether.It was found that the isomeric product ratio changes smoothly as a function of the annulation angles,not abruptly from one regioisomer to the other on going from five-to six-and seven-membered rings,as predicted by the Mills-Nixon effect.The relative amounts of the products were determined at four different temperatures,and assuming that the product ratio represents the relative rates ratio,the relative enthalpy of activations could be obtained.Theoretically(at B3LYP/6-31G* theoretical level)four different intermediates were considered.Each of these underwent angular angles deformations to model the two regioisomers.At each deforma-tion angle the energy difference between the two intermediates models was correlated to the experimental data for each of the four intermediates.It was found that the angle-deformed lithium(6-methyl-2-benzylium)pheno-late correlated best(R> 0.994)to the experimental data.This study confirms that the regioselectivity of the two isomeric oQMs in the oxidation of a-tocopherol and related compounds is simply a function of angular strain,best explained by the SIBL(strain-induced bond localization)model.In addition,this study provides evidence that the highest energy intermediate in the oxidation of vitamin E is a pheno-late-benzyl cation.
机译：文献中主要通过定义不明确的术语“ Mills-Nixon效应”解释了α-生育酚（维生素E的主要成分）氧化为邻醌甲基化物（oQM）的区域选择性。描述了11种α-生育酚衍生物的制备方法，这些衍生物彼此之间的夹角不同，但保持电子因子不变。这些化合物经过Ag2O氧化，形成了两个被乙烯基甲基醚捕获的异构体oQM。异构体产物比率随环角的变化而平稳变化，如Mills-Nixon效应预测的那样，在从五元环到六元环和七元环的过程中，一个区域异构体到另一个区域异构体不会突然变化。在四个不同的温度下测定，并假设产物比率代表相对速率比率，则可以获得相对的活化焓。理论上（在B3LYP / 6-31G *理论水平上）四个不同考虑了每种中间体，对每种中间体进行了角变形以对两种区域异构体进行建模，在每个变形角处，两种中间体模型之间的能量差与四种中间体各自的实验数据相关。角变形的6-（6-甲基-2-苄基）苯基锂锂与实验数据的相关性最好（R> 0.994）。该研究证实，两种异构体oQM在α-生育酚和相关化合物氧化中的区域选择性为简单地讲，它是角应变的函数，最好用SIBL（应变诱导的键定位）模型来解释。此外，这项研究提供了证据，证明维生素E氧化过程中最高的能量中间物是酚盐-苄基阳离子。

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