BIPHENYL-LINKED BIFLAVANOIDS FROM GRAPE POMACE

Two novel biphenyl linked biflavanoids commonly associated with polyph enol oxidase-coupled products were isolated from Chardonnay grape poma ce. Their chemical structures were established by long-range H,C coupl ings as epicatechin [6' --> 8]-epicatechin and epicatechin [6' --> 8] catechin. The disproportionate representation of the epicatechin unit as compared with catechin among the isolated biflavanoids could not be accounted for by their relative concentration in the pomace and sugge sted that the 2,3-trans configuration provided more steric constraints than the 2,3-cis one during grape polyphenol enzymatic oxidation of t he B-ring leading to the quinone intermediate. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.