Structures of two new oxidation products of green tea polyphenols generated by model tea fermentation

To clarify the oxidation mechanism of green tea catechins during tea fermentation, pure catechins were oxidized with a catechin-free homogenate of tea leaf. Oxidation of a mixture of (−)-epicatechin and (−)-epigallocatechin yielded a new metabolite, named dehydrotheaflavin, produced by the oxidation of a benzotropolone moiety of the black tea pigment theaflavin. Similar oxidation of a mixture of (−)-epicatechin and (−)-epigallocatechin 3-O-gallate afforded a new dimer of (−)-epigallocatechin 3-O-gallate, which was generated by the oxidation and cycloaddition of two pyrogallol rings. Structures were determined by spectroscopic method, and the oxidation mechanisms for the formation of the products were proposed.