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 biphenyl derivatives. Here, we report the isolation and structural characterization of two new 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‐3‐ O ‐[(4‐hydroxy‐3,5‐dimethoxyphenyl)prop‐2‐enoyl]‐ β ‐ D ‐fructofuranosyl}‐ α ‐ D ‐glucopyranoside; 11 ), and of four known compounds ( 12 – 15 ) from the MeOH extract of Polygala alpestris. The relative in vitro antioxidant activities of these compounds, in comparison with other phenolic substances from Polygala vulgaris , were evaluated by means of the Briggs Rauscher ( BR ) oscillating reaction, a method based on the inhibitory effects of 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.