抄録
Leaves of the tea plant (Camellia sinensis) were processed to various non-fermented and fermented tea products. During processing, tea catechins, such as epigallocatechin-3-O-gallate (1), are chemically converted to various products. However, many of the polyphenols of fermented tea products remains to be clarified. In this study, we first developed a biomimetic stereoselective method to prepare theasinensin A, which is a dimer of 1 and major black tea polyphenol. The method is one-pot reaction composed of two steps: oxidation of 1 with CuC12 and subsequent reduction of resulting quinone dimer with ascorbic acid. The reaction also yielded a tetramer of 1, which is probably related to uncharacterized oligomeric polyphenols of black tea. On the other hand, a new oxidation product of epicatechin was isolated from Chinese post-fermented tea, which is produced by aerobic fermentation with microorganisms. The structure suggested occurrence of oxidative cleavage of catechol-type B-ring with singlet oxygen, and it may be related to production of characteristic polymeric polyphenols of Chinese post-fermented tea. In contrast, Japanese post-fermented tea is produced by anaerobic fermentation process with microorganisms, and the tea products contained three phenolic compounds identical to the tea catechin metabolites produced by mammalian intestinal bacteria. In addition, we succeeded in preparation of the metabolites from tea catechin in vitro by anaerobic and aerobic methods using acetone powder of the Japanese post-fermented tea.
