56(P-13) カテキン及び関連ポリフェノールの酸化メカニズム(ポスター発表の部)

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Oxidation of green tea catechins under various conditions was chemically investigated. When a mixture of (-)-epicatechin (EC) and (-)-epigallocatechin (EGCG) was treated with homogenate of fresh tea leaves, theasinensin A and a new dimeric product 1, derived by Diels-Alder coupling of EGCG with its oxidation product, were obtained. On the other hand, auto-oxidation of theaflavin (TF) at pH 7.3 gave theanaphthoquinone (TNQ) and a new flavan-3-ol tetramer (2) having a bicyclooctane skeleton, which was also a Diels-Alder product of dehydro-TF and dihydro-TNQ. The results suggested that formation of quinehydrone type π-π complexes is important in the catechin oxidation. In the process of TF production from EC and (-)-epigallocatechin (EGC) by banana polyphenoloxidase, EC was rapidly oxidized to EC-quinone and the resulting EC-quinone oxidized EGC to EGC-quinone. After EGC was completely consumed, the EC-quinone began to oxidize TF to TNQ. This coupled oxidation mechanism was shown by rapid decrease of EGC in the presence of EC and the sparing of EC at the beginning of the reaction. In addition, when the reaction was conducted in the presence of glutathione, about 80% of EGC was not oxidized, even though EC was completely converted to its glutathione conjugates. Furthermore, it was also suggested that theasinensins (TS), dimers of EGC or EGCG found in black tea, were generated by reduction of corresponding quinones (TS-quinones) formed by stereospecific coupling of two EGC-quinones. The presence of TS-quinones in the homogenate of fresh tea leaves was also confirmed by isolation of their phenazine derivatives. These results suggested that thearubigins, the uncharacterized heterogeneous polymer of black tea, are probably produced by polymerization the quinones derived from catechins and their metabolites during tea fermentation.
天然有機化合物討論会の論文
2001-09-01

56(P-13) カテキン及び関連ポリフェノールの酸化メカニズム(ポスター発表の部)

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