Antioxidant Chemistry of Green Tea Catechins. Identification of Products of the Reaction of (−)-Epigallocatechin Gallate with Peroxyl Radicals

Abstract

(-)-Epigallocatechin gallate (EGCG), isolated from green tea, displays antioxidant properties and is thought to act as an antioxidant in biological systems. However, the specific mechanisms of its antioxidant actions remain unclear. In this study, we have isolated and identified for the first time two reaction products of EGCG derived from its reaction with peroxyl radicals generated by thermolysis of the initiator 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN). The products include a seven-membered B-ring anhydride and a novel dimer. The identification of these products provides the first unambiguous proof that the principal site of antioxidant reactions on the EGCG molecule is the trihydroxyphenyl B ring, rather than the 3-galloyl moiety. In contrast to phenoxyl radicals from simple phenolic antioxidants, an initially formed EGCG phenoxyl radical apparently does not form stable addition products with AMVN-derived peroxyl radicals. Characteristic reaction products may provide novel markers for EGCG antioxidant reactions in living systems.

Oxidation of Tea Catechins: Chemical Structures and Reaction Mechanism

“…4). The same model fermentation experiment yielded another known dimer (15) (Tanaka et al, 2002b), which has recently been reported as an oxidation product obtained by treatment of 4 with a radical initiator in an organic solvent (Valcic et al, 1999) and with peroxidase-H 2 O 2 . Besides production of theaflavins, formation of these dimeric products from epigallocatechin and its gallate is an alternative major metabolic pathway of tea catechins.…”

“…However, the major part of these metabolites probably derive from epigallocatechin (2) and its gallate (4), because these two catechins together account for over 70% of the total tea catechins in fresh tea leaves. There have been a number of reports on enzymatic and non-enzymatic oxidation of epigallocatechin and its gallate, and most of them have suggested that oxidation and subsequent intermolecular condensation between two pyrogallol B-rings dominantly occurred (Hashimoto et al, 1988;Tanaka et al, 2001;Tanaka et al, 2002b;Valcic et al, 1999;Zhu et al, 2000). In black tea, the most important metabolites derived from 2 and 4 are theasinensins (11), in which pyrogallol rings of two molecules of epigallocatechin or its gallate are linked through the C-C bond.…”

Green Tea Component, Catechin, Induces Apoptosis of Human Malignant B Cells via Production of Reactive Oxygen Species

“…Previous studies on the antioxidative property of (À)-epigallocatechin-3-gallate have shown both the trapping effect of ROS as well as the inhibitory effect of lipid peroxidation (38). However, after neutralizing the peroxyl or other radicals, (À)-epigallocatechin-3-gallate itself could be converted to phenoxyl radical (39).…”

Green tea extracts attenuate doxorubicin-induced spermatogenic disorders in conjunction with higher telomerase activity in mice

“…The exact mechanisms of action of green tea polyphenols remain obscure, but it is known that these substances possess antioxidative capacity derived from their ability to scavenge reactive oxygen species and trap hydroxyl and peroxyl radicals. The in vitro antioxidant capacity of teas and tea polyphenols has been assessed using several different approaches [4][5][6]. Moreover, antioxidative effects of tea polyphenols have been reported in humans [7][8][9].…”