Analysis of commercial proanthocyanidins. Part 3: the chemical composition of wattle (Acacia mearnsii) bark extract

Abstract

Wattle (Acacia mearnsii) bark extract is an important renewable industrial source of natural polymers for leather tanning and adhesive manufacturing. The wattle bark proanthocyanidin oligomers have 5-deoxy extender units that render the interflavanyl bonds resistant to acid catalysed hydrolysis and their composition cannot be determined via conventional thiolysis. We combined established phyto- and synthetic chemistry perspectives with an electrospray mass spectrometry investigation to establish that the flavan-3-ol based oligomers consist of a starter unit which is either catechin or gallocatechin, angularly bonded to fisetinidol or predominantly robinetinidol extender units.