Lignans, flavonoids and coumarins from Viola philippica and their α-glucosidase and HCV protease inhibitory activities.

Two lignans including a new one, five flavonoids and five coumarins were isolated from the whole plant of Viola philippica (synonymised as Viola yedoensis Makino). The new compound was structurally determined as (7R,8S,8'S) -3,3'-dimethoxy- 4,4',9-trihydroxy- 7,9'-epoxy-8,8'-lignan 9-O-rutinoside by analysis of its NMR, MS and CD spectroscopic data. The known compounds were characterised by comparing their NMR and MS data with those reported. Among the known compounds, 5-hydroxy-4'-methoxyflavone-7-O- rutinoside, 6,7-di-O-β-D- glucopyranosylesculetin, and 7R,8S-dihydrodehydrodiconiferyl alcohol 4-O-β-D- glucopyranoside were isolated and identified from this genus for the first time. Of these compounds, 5-hydroxy-4'-methoxyflavone-7-O-rutinoside and (7R,8S,8'S) -3,3'-dimethoxy- 4,4',9-trihydroxy- 7,9'-epoxy-8,8'-lignan 9-O-rutinoside were potently active against α-glucosidase, while the two dimeric coumarins, 5, 5'-bi (6, 7-dihydroxycoumarin) and 6,6',7,7'-tetrahydroxy-5,8'-bicoumarin potently inhibited HCV protease.