Synthesis of condensed tannins. Part 6. The sequence of units, coupling positions and absolute configuration of the first linear [4,6 : 4,6]-triflavanoid with terminal 3,4-diol function

Abstract

The first linear triflavanoid with a terminal 3,4-diol function, (2R,3S,4S : 2′R,3′S,4′R : 2″R,3″S,4″R)-[4,6 : 4,6]-bi-[(–)-fisetinidol]-(+)-mollisacacidin, is associated with a set of four diastereoisomeric biflavanoid homologues, [4,6]-(–)-fisetinidol-(+)-mollisacacidins, in the heartwood of the black wattle tree, Acacia mearnsii. The sequence of units in the triflavanoid and its bonding points have been determined by n.m.r. spectroscopy at 500 MHz using spin-decoupling techniques. The triflavanoid and two biflavanoids with (2R,3S,4S)-2,3-trans-3,4-cis-configurations in their ‘upper’ units, result from the in vitro self-condensation of their putative precursor (2R,3S,4R)-flavan-3,3′,4,4′,7-pentaol[(+)-mollisacacidin], thus permitting definition of their respective absolute configurations.