Study on structural identification and antioxidant activity of flavonoids from jujube leaves

Five kind of flavonoids in the jujube leaves were obtained by the isolation with ethanol as the extraction reagent and subsequently purification of ethyl acetate fraction of the ethanol extract by a preparative HPLC, whose structures were verified by1 H NMR and13 C NMR. The five compounds were identified as quercetin-3-O-robinobioside (1) , quercetin-3-O-rutinoside (2) , quercetin-3-O-β-D-glucoside (3) , kaempferol-3-Orutinoside (4) and quercetin-3-O-α-L-arabinosyl- (1→2) -α-L-rhamnoside (5) , respectively. All compounds were evaluated for antioxidant capacity against ABTS+and DPPH radicals. Results revealed similar trends for the capability of the five flavonoids to scavenge the ABTS+and DPPH radicals. Among them, compound 3exhibited the highest activity and compound 1, 2, and 5 showed moderate activity, while compound 4 revealed lower antioxidant capacity.