Three new flavonol glycosides from Fissistigma pallens

Three new flavonol glycosides, fissflavosides A-C (1-3), together with six known flavonol glycosides, kaempferol 3-O-α-L-rhamnopyranosyl-(1→2)-β-D-galactopyranoside (4), kaempferol 3-O-α-L-rhamnopyranosyl-(1→6)-β-D-galactopyranoside (5), kaempferol 3-O-α-L-rhamnopyranosyl-(1→6)-β-D-glucopyranoside (6), rhamnetin 3-O-α-L-rhamnopyranosyl-(1→2)-β-D-glucopyranoside (7), rutin (8), and isorhamnetin 3-O-α-L-rhamnopyranosyl-(1→2)-β-D-galactopyranoside (9) were isolated from the methanol extract of the Fissistigma pallens leaves. Their chemical structures were determined by 1D-, 2D-NMR, and MS data as well as in comparison with reported data in the literature. Compounds 1-9 showed weak cytotoxic activity on three human cancer cell lines, HT-29, A-2058, A-549 with IC₅₀ ranging from 134.6 to 162.6 µM. In addition, the antioxidant capacities of compounds were also tested by ORAC assay. All compounds showed significant antioxidant with trolox equivalents ranging from 4.4 to 8.6 µM at the concentration of 1.0 µM. The results indicated 7 and 8 having meaningful reducing capacity of copper (I) ions of 2.7 to 6.9 µM at the concentrations of 1 and 2 µM.