Furostanol Saponins from the Bulbs of Welsh Onion, Allium fistulosum L.

Abstract

An extensive phytochemical analysis of the polar extracts from bulbs ofWelsh onion Allium fistulosum L. led to the isolation of nine saponins, four of them, named fistulosaponins G (1a/1b), H (2), I (3a/3b), and J (4), have never been reported previously. Fistulosaponins G and I were isolated as a couple of isomers in equilibrium. On the basis of 2D NMR and mass spectrometry data, the structure of the novel compounds were elucidated as (25R)-26-(beta-D-glucopyranosyl) oxy-3 beta, 22 beta-dihydroxyfurost- 5-en-1 beta-yl O-alpha-L-rhamnopyranosyl-(1 -> 4)-O-alpha-L-rhamnopyranosyl-(1 -> 4)-beta-Dglucopyranoside (1a) with its 22a epimer (1b), (25R)-26-(beta-D-glucopyranosyl) oxy-3 beta-hy-droxyfurost-5,20-dien-1 beta-yl O-alpha-L-rhamnopyranosyl-(1 -> 4)-O-alpha-L-rhamnopyranosyl-(1 -> 4)-beta D- glucopyranoside (2), (25R)-26-(beta-D-glucopyranosyl) oxy-3 beta, 22 beta-dihydroxyfurost-5-en-1 beta-yl O-alpha-L-rhamnopyranosyl-(1 -> 4)-beta-D-glucopyranoside (3a) with its 22a epimer (3b), and (25R)26-(beta-D-glucopyranosyl) oxy-3 beta-hydroxyfurost5,20- dien-1 beta-yl O-alpha-L-rhamnopyranosyl-(1 -> 4)beta- D-glucopyranoside (4).This is the first report of furostanol saponins in A. fistulosum bulbs. In addition, data on the antibacterial tests of the isolated saponins against Escherichia coli and Enterococcus faecalis are reported.