Some stereochemically identical biflavanols from the bark tannins of Acacia mearnsii

Abstract

The homologous series of biflavanols leucofisetinidin-(+)-catechin, leucorobinetinidin-(+)-catechin, and leucoro-binetinidin-(+)-gallocatechin are prominent components amongst the bark tannins of the black wattle (A. mearnsii). High resolution nuclear magnetic resonance and mass spectra of some of their derivatives are consistent with identical 2,3-trans-3,4-trans:2′,3′-trans configurations of each, and 2(eq),3(eq),4(eq):2′(eq),3′(eq) arrangements of substituents in their heterocyclic C- and F-rings, respectively. Their constituent flavanol units are 4,6(4,8)-linked giving stabilised half-chair conformations to their C-ring systems.

Their immediate biosynthetic precursors are, apparently, the associated flavan-3,4-diols and flavan-3-ols of similar configuration.