Oxidative dimers produced from protocatechuic and gallic esters in the DPPH radical scavenging reaction
Oxidative dimers produced from protocatechuic and gallic esters in the DPPH radical scavenging reaction
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DOI：
10.1021/jf020347g
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发表时间：
2002-09-11
影响因子：
6.1
通讯作者：
Kasai, T
中科院分区：
文献类型：
--
作者：
Kawabata, J;Okamoto, Y;Kasai, T
采用核磁共振技术研究了原儿茶酸和没食子酸及其甲酯的DPPH（2,2-二苯基-1-苦味酰肼基）自由基清除反应。在丙酮中，原儿茶酸甲酯在与DPPH自由基的反应中逐渐转化为两个中间醌分子的Diels-Alder加合物，而没食子酸甲酯则通过假定的醌前体迅速转化为对称二聚体。这两种二聚体都相当不稳定，它们的结构已经通过对反应混合物的原位核磁共振测量推断出来。没食子酸和没食子酸甲酯在同样的反应中也产生了相应的对称二聚体，尽管由原儿茶酸产生的原儿茶醌不像它的甲酯那样产生Diels-Alder加合物。有趣的是，在甲醇溶液中没有观察到这些二聚体的形成。
DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging reactions of protocatechuic and gallic acids, and their methyl esters, have been investigated by NMR. In acetone, methyl protocatechuate was gradually converted to a Diels-Alder adduct of two molecules of the intermediate quinone in the reaction with DPPH radical, whereas methyl gallate rapidly gave a symmetrical dimer via a putative quinone precursor. Both dimers are rather unstable and their structures have been deduced by in situ NMR measurements of the reaction mixtures. Gallic acid also gave a corresponding symmetrical dimer in the same reaction as methyl gallate, although protocatechuquinone produced from protocatechuic acid did not yield a Diels-Alder adduct, unlike its methyl ester. Interestingly, these dimer formations were not observed in methanol solution.