Flavonoid composition and antimicrobial activity of Cirsium rivulare (Jacq.) All. flowers.

A new flavonoid compound isokaempferide 7-O-beta-d-(6''-methylglucuronide) (1) was isolated from flowers of Cirsium rivulare (Jacq.) All. Its structure was elucidated on the basis of spectroscopic studies (UV, (1)H and (13)C NMR, FABMS). Moreover, five known flavonoid compounds: apigenin 7-(6''-methylglucuronide) (2), hispidulin 7-glucoside (3), isokaempferide 7-glucuronide (4), kaempferol 3-galactoside (5), pectolinarin (6) were isolated from this source for the first time. The antimicrobial activity of aqueous, methanolic and 70% ethanolic extracts of Cirsium rivulare flowers and leaves was also evaluated.