Kaempferol glycosides and cardenolide glycosides, cytotoxic constituents from the seeds of Draba nemorosa (Brassicaceae)

Bioassay-directed fractionation of a methanolic extract from the seeds of Draba nemorosa (Brassicaceae) led to isolation of a new flavonol glycoside, drabanemoroside (5, kaempferol 3-O-α-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranose) along with four known flavonoid derivatives (1–4), four cardenolide glycosides (6–9). Kaempferol glycosides 2 and 5 showed strong cytotoxicity against human small lung cancer cell line A549 and melanoma SK-Mel-2 with an IC50 of 0.5 μg/mL and 1.9 μg/mL, respectively. Cardenolide glycosides 6–9 showed potent cytotoxicity (A549) in the range of 0.01–0.032 μg/mL. Their structures were characterized based on spectroscopic data (2D NMR, HRTOFMS, IR, and UV) and comparison of literature values. The carbohydrate units were also confirmed by comparing the hydrolysate of 5 with authentic monosaccharides.