Graduate School of Integrated Arts and Science, University of Tokushima , Tokushima 770-8502, Japan.
J Agric Food Chem. 2012 May 23;60(20):5142-51. doi: 10.1021/jf3008822. Epub 2012 May 14.
Chemical interaction between polyphenols and thiols was investigated under radical oxidation conditions using a model cysteinyl thiol derivative, N-benzoylcysteine methyl ester. The radical oxidation was carried out with a stoichiometric amount of 2,2-diphenyl-1-picrylhydrazyl (DPPH), and the decreases in the amounts of polyphenols and the thiol were measured by HPLC analysis. Cross-coupling products between various polyphenols and the thiol were examined by LC-MS in reactions that showed decreases in both the polyphenols and the thiol. The LC-MS results indicated that three phenolic acid esters (methyl caffeate, methyl dihydrocaffeate, and methyl protocatechuate) and six flavonoids (kaempferol, myricetin, luteolin, morin, taxifolin, and catechin) gave corresponding thiol adducts, whereas three polyphenols (methyl ferulate, methyl sinapate, and quercetin) gave only dimers or simple oxidation products without thiol substituents. Thiol adducts of the structurally related compounds methyl caffeate and methyl dihydrocaffeate were isolated, and their chemical structures were determined by NMR analysis. The mechanism for the thiol addition was discussed on the basis of the structures of the products.
采用 N-苯甲酰半胱氨酸甲酯作为模型半胱氨酸巯基衍生物，研究了多酚与硫醇在自由基氧化条件下的相互作用。自由基氧化是用化学计量的 2,2-二苯基-1-苦基肼（DPPH）进行的，通过 HPLC 分析测量多酚和硫醇的减少量。通过 LC-MS 检查了在显示多酚和硫醇减少的反应中各种多酚和硫醇之间的交叉偶联产物。LC-MS 结果表明，三种酚酸酯（咖啡酸甲酯、二氢咖啡酸甲酯和原儿茶酸甲酯）和六种类黄酮（山柰酚、杨梅素、木樨草素、桑色素、杨梅素和儿茶素）生成相应的巯基加合物，而三种多酚（阿魏酸甲酯、芥子酸甲酯和槲皮素）仅生成没有巯基取代基的二聚体或简单氧化产物。分离出结构相关化合物甲基咖啡酸和甲基二氢咖啡酸的巯基加合物，并通过 NMR 分析确定其化学结构。根据产物的结构讨论了巯基加成的机理。
