Base-Catalyzed Reactions of (−)-Epicatechin: Formation of Enantiomers of Base-Catalyzed Reaction Products from (+)-Catechin

Three compounds were isolated from the base-catalyzed reaction products of (−)-epicatechin at pH 12 and 40°C. From the results of the NMR and CD measurements, these were revealed to be the enantiomers of catechinic acid, catechinic acid stereoisomer and diarylpropanol-catechinic acid dimer formed from the base-catalyzed reactions of (+)-catechin. Thus, it has been demonstrated that both rearrangement and dimerization reactions as well as epimerization take place in the base-catalyzed reaction of (−)-epicatechin, similar to that of (+)-catechin. These results support that the quinone methide intermediate is formed during the base-catalyzed reactions, and the configuration of the hydroxyl group at C-3 should influence significantly the stereoselectivity of the subsequent reactions.