Formation of a Novel Catechinic Acid Stereoisomer From Base-Catalyzed Reactions of (+)-Catechin

A novel catechinic acid stereoisomer, 6-(3,4-dihydroxyphenyl)-7,9-epoxy-9-hydroxy-bicyclo[3.3.1]nona-2,4-dione was isolated from base-catalyzed reaction products of (+)-catechin at pH 12 and 40°C. The 6S absolute configuration of this compound has been confirmed from its 1H-NMR coupling constants, while the 6R configuration was previously reported for catechinic acid. The formation of a novel catechinic acid stereoisomer shows that the rearrangement of (+)-catechin to catechinic acid through the quinone–methide intermediate is not stereospecific but stereoselective.