Antioxidant flavonoids from leaves of Polygonum hydropiper L.

Abstract

Ten flavonoid compounds were isolated from the dried leaves of Polygonum hydropiper L. (Laksa leaves), and identified as 3- O-α- l-rhamnopyranosyloxy-3′,4′,5,7-tetrahydroxyflavone; 3- O-β- d-glucopyranosyloxy-4′,5,7-trihydroxyflavone; 6-hydroxyapigenin; 6″- O-(3,4,5-trihydroxybenzoyl) 3- O-β- d-glucopyranosyloxy-3′, 4′, 5, 7-tetrahydroxyflavone; scutillarein; 6-hydroxyluteolin; 3′,4′,5,6,7-pentahydroxyflavone; 6-hydroxyluteolin-7- O-β- d-glucopyranoside; quercetin 3- O-β- d-glucuronide; 2″- O-(3,4,5-trihydroxybenzoyl) quercitrin; quercetin. Evaluation of the antioxidative activity, conducted in vitro, by using electron spin resonance (ESR) and ultraviolet visible (UV–vis) spectrophotometric assays, showed that these isolated flavonoids possess strong antioxidative capabilities. Measurement of the Trolox equivalent antioxidant capacity (TEAC) values, against ABTS (2,2′-azinobis(3-ethyl-benzo-thiazoline-6-sulphonic acid) radicals and phenyl- tert-butyl nitrone (PBN) azo initiator (AI) also showed strong anti-oxidative activity. The most powerful of the antioxidants was 2″- O-(3,4,5-trihydroxybenzoyl) quercitrin (galloyl quercitrin). A combination of two flavonoid compounds was tested for synergistic anti-oxidative capacity, but no significant improvement was observed.