Stereochemical Revision of Brevipetins E and F: Opposite Hexahydroxydiphenoyl Atropisomerism in Ellagitannin Dimers Revealed by DFT-Based Spectroscopic Analysis

Brevipetins E and F, ellagitannin dimers from Cleidion brevipetiolatum, were originally reported to bear both a 3,4-(Ra)-hexahydroxydiphenoyl (HHDP)-glucopyranose and a 3,4-(Ra)-HHDP-rhamnopyranose moiety. However, a detailed reevaluation of the reported electronic circular dichroism (ECD) data, supported by DFT-based 1H and 13C NMR chemical shift and ECD calculations, supports a stereochemical reassignment of these ellagitannins. Accordingly, the 3,4-HHDP-rhamnopyranose moiety in these compounds is reassigned to the (Sa)-atropisomeric configuration, in line with the observed reduction in Δε magnitudes relative to the constituent monomers.