Flavonol glycosides from the aerial parts of Aceriphyllum rossii and their antioxidant activities

The methanol extract obtained from the aerial parts of Aceriphyllum rossii (Saxifragaceae) was fractionated into ethyl acetate (EtOAc), n-BuOH and H2O layers through solvent fractionation. Repeated silica gel column chromatography of EtOAc and n-BuOH layers afforded six flavonol glycosides. They were identified as kaempferol 3-O-beta-D-glucopyranoside (astragalin, 1), quercetin 3-O-beta-D-glucopyranoside (isoquercitrin, 2), kaempferol 3-O-alpha-L-rhamnopyranosyl (1-->6)-beta-D-glucopyranoside (3), quercetin 3-O-alpha-L-rhamnopyranosyl (1-->6)-beta-D-glucopyranoside (rutin, 4), kaempferol 3-O-[alpha-L-rhamnopyranosyl (1-->4)-alpha-L-rhamnopyranosyl (1-->6)-beta-D-glucopyranoside] (5) and quercetin 3-O-[alpha-L-rhamnopyranosyl (1-->4)-a-L-rhamnopyranosyl (1-->6)-beta-D-glucopyranoside] (6) on the basis of several spectral data. The antioxidant activity of the six compounds was investigated using two free radicals such as the ABTS free radical and superoxide anion radical. Compound 1 exhibited the highest antioxidant activity in the ABTS {2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)} radical scavenging method. 100 mg/L of compound I was equivalent to 72.1+/-1.4 mg/L of vitamin C, and those of compounds 3 and 5 were equivalent to 62.7+/-0.5 mg/L and 54.3+/-1.3 mg/L of vitamin C, respectively. And in the superoxide anion radical scavenging method, compound 5 exhibited the highest activity with an IC50 value of 17.6+/-0.3 muM. In addition, some physical and spectral data of the flavonoids were confirmed.