P-54 紅茶色素テアフラビン類の生成機構の解明(ポスター発表の部)

概要

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Theaflavins, one of the major black tea pigments containing benzotropolone skeleton, are formed by oxidative coupling of catechol type and pyrogallol type catechins. Although many studies for the reaction mechanism had been reported, the exact mechanism was not reported until now. Now we report the full formation mechanism of benzotropolone skeleton. First, an efficient synthesis of the 8, 9-dihydrobenzotropolone (7) as a model compound of the theaflavins was succeeded by adding pyrogallol (6) after oxidation of the catechol (5) by the treatment of K_3Fe(CN)_6 in over 70% yield (Fig.3). Therefore, the first step in benzotropolone-ring formation mechanism was indicated as follows: first, the catechol (5) become the o-quinone by the oxidation, next, the pyrogallol (6) nucleophillic attacked to it (Fig.2, C). And, 4-Methyl-o-benzoquinone (9) prepared from 4-methylcatechol (8) was coupled with 4-methylpyrogallol (10) to give bicyclo[3.2.1] derivative (12) in quant. yield (Fig.5). (12) was easily hydrolyzed with H_2O to give 4,6-dimethyl benzotropolone (11) in 94% yield. Thus, we succeeded in proving the formation mechanism of the theaflavins (Fig. 6).
2006-09-15