Crystal structure and absolute configuration of (–)-3-O-acetyl-6-bromo-3′,4′,5,7-tetra-O-methylepicatechin, a reference compound for the aromatic bonding positions of 2,3-cis-procyanidins

Abstract

Determination of the structure of (–)-(2R,3R)-3-O-acetyl-6-bromo-3′,4′,5,7-tetra-O-methylepicatechin in the crystalline state confirmed the position of bromination and hence that of its 8-bromo isomer; both are key reference compounds for assessing the aromatic bonding positions in 2,3-cis-procyanidins. The half-chair conformation of the heterocyclic ring is shown to be in close agreement with the published structure of (–)-epicatechin. Determination of the absolute configuration of the derivative, in accord with earlier chemical evidence, is shown to hinge on detailed refinement of an extended data set.