Condensed tannins (CTs) consist of oligomers and polymers of flavan-3-ol subunits varying in hydroxylation patterns, cis- and trans-configuration of C-ring substituents, interflavan bond connections, mean degree of polymerization (mDP) and extent of esterification. Robust analytical methods to determine CT composition and structure are paramount to understanding the biological activity exerted by these secondary plant metabolites in human health, agriculture and environmental systems. Using a combination of wet chemistry data from thiolytic degradation, mass spectrometry and two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy, progress in the structural elucidation of purified CTs has been made. We have previously shown that integration of the 2D NMR cross-peaks signals for procyanidin/prodelphinidin (PC/PD) and cis/trans flavan-3-ol subunit provides relative ratios that corroborated thiolytic data. Recent progress of CT structure elucidation using these methods in concert allows the identification and content estimations of the terminal flavan-3-ol subunits, the extent of galloylation, ratios of A-type to B-type interflavan linkages and mDP of purified CT samples. In addition, a second set of 2D NMR cross-peaks signals (H/C-2) can provide reliable determination of flavan-3-ol cis/trans ratios. These advances will aid in the formulation of CT structure-biological activity relationships.

Coupling of wet chemistry methods and spectroscopic data for elucidating composition and structure of purified condensed tannins

255th National Meeting (2018)

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