Unambiguous investigation of condensed tannin (CT) structure-activity relationships in biological systems requires the use of highly enriched CT fractions of defined chemical purity. Purification of CTs from Sorghum bicolor, Trifolium repens, Theobroma cacao, Lespedeza cuneata, Lotus pedunculatus and Lotus corniculatus was accomplished by Sephadex LH-20 chromatography using gradient elution schemes. We found that the degree of CT enrichment and need for further purification by chromatography could be rapidly assessed in minutes by subjecting fractions to 1H NMR spectroscopy. These assessments were independently corroborated by a more time-consuming but quantitative thiolysis procedure. Further examination of CT fractions by 1H-13C HSQC NMR spectroscopy provided a more detailed assessment of impurities, some of which (carbohydrate- and lipid-derived) avoid detection by UV absorption-based detectors commonly used for CT chromatography. Researchers can now rely on a rapid 1H NMR analysis to assess the purity of CT fractions, even with low-field (360 MHz) NMR instruments.

Purity assessment of condensed tannin fractions by nuclear magnetic resonance (NMR) spectroscopy

248th National Meeting (2014)

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