[Study on antioxidant activity of flavonoids from leaves of Psidium guajava].

The present study is to study the chemical constituents from ethanol extract of Psidium guajava leaves. The constituents were separated and purified by silica gel column chromaiographios over, macroporous resin D-101, Sephadex LH-20, and ODS. Six flavonoids compounds were isolated and identified as quercetin(1), quercetin-3---D-arabinopyranoside(2), quercetin-3---D-ribopyranoside(3), quercetin-3---D-galactopyranoside(4), quercetin-3---D-glucopyranoside(5), and quercetin-3--D-xylpyranoside(6). The antioxidant effects of six flavonoids was evaluated by scavenging ability of DPPH, superoxide anion, ABTS·⁺, and reducing effect of Fe³⁺ as well as total antioxidant capacity(FRAP). Vitamin C was used as positive control. The results indicated that six flavonoids exhibited significant antioxidant effects.