P-78 カテキン類及びテアフラビン類の異性化反応機構と改良異性化法の開発(ポスター発表の部)

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Epimerization of green tea catechins at C-2 position during the sterilization step has been studied. It was reported that these catechin epimers have more biological activities than the original catechins. Until now degradation and polymerization of catechins by oxidation couldn't be avoided in epimerization condition. Therefore we started to develop novel efficient method (s) to prepare the catechin epimers. Although it reported that catechin epimers was hardly obtained in pH 7 condition, we succeeded in epimerization of catechins to give catechin epimers in 55% yield respectively by introducing N_2 gas into the catechins buffer solution (pH 7) at 80℃ in. Furthermore, we also succeeded in isomerization of catechins in strong acidic condition in 1% H_2SO_4/ROH in which protonation at oxygen in ether ring promote the epimerization catechins. Such acidic isomerization with H_2SO_4 were especially useful for gallate-type catechins such as EGCg or ECg in 70% yield. Each theaflavins, one of the major black tea pigments, also gave only one corresponding epimers in weak alkaline condition (pH 8, 100℃). The structure was determined to be (10) by preparations of possible four isomers from catechins.
2008-09-01