Three diastereoisomeric 4,6-linked bileucofisetinidins from the heartwood of Acacia mearnsii

Abstract

Three diastereoisomeric bileucofisetinidins from the heartwood tannins of the black wattle tree (Acacia mearnsii) are isolated individually as their crystalline hexamethyl ethers. Analysis of the high-resolution nuclear magnetic resonance and mass spectra of the hexamethyl ether triacetates shows the component flavanol units to be 4,6-linked, and the derivatives to have the 2,3-trans-3,4-cis:2,3-trans-3,4-trans; 2,3-trans-3,4-cis:2,3-trans-3,4-cis; and 2,3-trans-3,4-trans:2,3-trans-3,4-trans relative configurations. The 2,3-trans-3,4-cis C rings of the former pair exist in an unusual boat conformation.

The methyl ether of the 2,3-trans-3,4-cis:2,3-trans-3,4-trans bileucofisetinidin forms an isopropylidene derivative of the 2,3-trans-3,4-cis:2,3-trans-3,4-cis diastereoisomer by inversion of the 4-hydroxyl of the former.