Antioxidant Activity and Proanthocyanidin Profile of Selliguea feei Rhizomes

Proanthocyanidins from the rhizomes of Selliguea feei (PSFs) were solvent-extracted and fractionated by Sephadex LH-20 column chromatography to give a 2.42% isolated yield (dry matter basis). 1H-NMR spectroscopy revealed the mean degree of polymerization (mDP) to be 2.6. 13C-NMR analysis showed typical signals for afzelechin/epiafzelechin units. Clear peaks at 76 ppm and 84 ppm indicated that both stereoisomers (afzelechin/epiafzelechin) are present. In agreement with the NMR spectra, the ESI-MS spectrum indicated that PSFs are mainly monomers to trimers consisting of afzelechin/epiafzelechin units with A-type and B-type interflavanyl linkages. A trimer was purified and identified as demethylated selligueain B. Thiolysis confirmed the structure and the thiolytic products, methyl 2-[(2 R, 3 R, 4 S)-3,5,7-trihydroxy-2-(4-hydroxyphenyl)chroman-4-yl]acetate ( 1) and 4β-(carboxymethyl)sulphanylepiafzelechin-(2β→O→7,4β→8)-epiafzelechin methyl ester ( 2), were purified and characterized. Selligueain A, demethylated selligueain B, compounds 1 and 2 possess high antioxidant capacity at 1.18 × 10 4, 1.16 × 10 4, 0.95 × 10 4 and 1.29 × 10 4 μmol TE/g, respectively.