51(P-17) 紅茶に含まれるエピガロカテキン二量体テアシネンシン類の生成機構(ポスター発表の部)

概要

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Enzymatic oxidation of epigallocatechin 3-O-gallate yielded dehydrotheasinensin A along with 2,3,5,7-tetrahydroxychroman-3-O-gallate and a known dimer of the quinone of epigallocatechin gallate. Dehydrotheasinensin A possesses a hydrated cyclohexentrione ring and is chemically equivalent to a quinone of theasinensin A, which was shown to be accumulated at initial stage of black tea manufacturing. Reduction of dehydrotheasinensin A with ascorbic acid or thiol compounds gave theasinensin A, a major phenolic constituent of black tea, in which two molecules of epigallocatechin gallate were connected by R-biphenyl bond between two B-rings. On the other hand, when the aqueous solution was heated, dehydrotheasinensin A was converted to theasinensin D, an S-atropisomer of theasinensin A, along with galloyl oolongtheanin. Furthermore, in phosphate buffer at pH6.8 at room temperature, dehydrotheasinensin A was converted to theasinensins A and D, galloyl oolongtheanin and an oxidation product which suffered an oxidative cleavage of the cyclohexenone ring. The results substantiated an assumption that epigallocatechin dimers in black tea were produced by dismutation of the corresponding theasinensin o-quinones. Furthermore, it was confirmed that dehydrotheasinensin A was produced by autoxidation of epigallocatechin-3-O-gallate in neutral aqueous solution.
天然有機化合物討論会の論文
2003-09-01