Antioxidant chemistry of green tea catechins. Identification of products of the reaction of (-)-epigallocatechin gallate with peroxyl radicals

(-)-Epigallocatechin gallate (EGCG), isolated from green tea, displays anti oxidant properties and is thought to act as an antioxidant in biological sy stems. However, the specific mechanisms of its antioxidant actions remain u nclear. In this study, we have isolated and identified for the first time t wo reaction products of EGCG derived from its reaction with peroxyl radical s generated by thermolysis of the initiator 2,2'-azobis(2,4-dimethylvaleron itrile) (AMVN), The products include a seven-membered B-ring anhydride and a novel dimer. The identification of these products provides the first unam biguous 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 init ially formed EGCG phenoxyl radical apparently does not form stable addition products with AMVN-derived peroxyl radicals. Characteristic reaction produ cts may provide novel markers for EGCG antioxidant reactions in living syst ems.