Competition between (+)-catechin and (-)-epicatechin in acetaldehyde-induced polymerization of flavanols

The reactions of (+)-catechin and (-)-epicatechin in the presence of acetal dehyde were studied in model solution systems. When incubated separately wi th acetaldehyde and at pH values varying from 2.2 to 4.0, reactions were fa ster with (-)-epicatechin than with (+)-catechin. In mixtures containing bo th (+)-catechin and (-)-epicatechin with acetaldehyde, new compounds beside s the homogeneous bridged derivatives were detected. These compounds were c oncluded to be he heteroligomers consisting of (+)-catechin and (-)-epicate chin linked with an ethyl bridge. In this case, the reaction of (-)-epicate chin was faster than that of (+)-catechin. This was also observed in soluti ons containing the two flavanols and the (+)-catechin-ethanol intermediate. Under these conditions, the homogeneous (+)-catechin bridged dimers and he terogeneous dimers were obtained by action of the intermediate on (+)-catec hin and (-)-epicatechin, respectively. In addition, the homogeneous (-)-epi catechin ethyl-bridged dimers were also detected, showing that ethyl linkag es underwent depolymerization and recombination reactions.