Polyphenols from Polygala spp. and their antioxidant activity

Members of Polygalaceae are known to contain a variety of different polyphenolic compounds such as xanthones, flavonoids and diphenylderivatives. Here, we report the isolation and structural characterization of two phenol derivatives, named Alpestrin (= 3,3’,5’-trimethoxy[1,1’-biphenyl]-4-ol;10)) and Alpestriose A (=6-O-benzoyl-1-O-6-O-acetyl-[4-hydroxy-3,5-dimethoxyphenyl)prop-2-enoyl] --D-fructofuranosyl--D-glucopyranoside; 11), and of four known compounds (12-15) from the methanolic extract of Polygala alpestris. The relative in vitro antioxidant activities of these compounds, and in comparison with other phenolic substances from Polygala vulgaris, were evaluated by means of the Briggs-Rauscher (BR) oscillanting reaction, a method based on the inhibitory effects by antioxidant free-radical scavengers. The experimental antioxidant activity values (relative to resorcinol as a standard) were compared with those calculated on the basis of the bond-dissociation enthalpies. The structure/activity relationships for the compounds examined are also discussed.