A novel flavonol glycoside and six derivatives of quercetin and kaempferol from Clematis flammula with antioxidant and anticancer potentials

Clematis flammula leaves are traditionally used in Algeria to treat rheumatoid arthritis. Our aim was to identify the main compounds in this plant in order to characterize its antioxidant and anticancer activities. A new flavonol compound, kaempferol 3-O-[(6-O- caffeoyl)- glucosyl(1 → 2)]-(6-Ocaffeoyl) glucoside-7-O-rhamnoside (6) along with six known flavonol molecules were isolated from an ethanolic extract of Clematis flammula leaves. The chemical structures of these flavonols were elucidated using NMR and high resolution-MS spectroscopies. Antioxidant activities of the extract were revealed through its elimination of superoxide radical (O2.-) produced enzymatically (49.7 ± 1.52% at 50 μg/ml) and non-enzymatically (34 ± 1.2% at 100 μg/ml), probably related to its inhibition of the xanthine oxidase form of the xanthine oxidoreductase (XOR) enzyme (25.05 ± 2.33 μg/mL at 100 μg/mL), but mostly to that of the NADH oxidase form of the enzyme (69.16 ± 4.0%). Cytotoxicity tests of the extract on human hepatoma cell line HepG2 and ovarian cancer cell lines A2780 and OVCAR3 were promising especially regarding A2780 cell line (IC50: 77.0 μg/mL), which was comparable to taxol (IC50:76.9 μg/mL).