Chemical Composition of Shallot (Allium ascalonicum Hort.)

An extensive phytochemical analysis of the polar extracts from bulbs of shallot, Allium ascalonicum Hort., led to the isolation of two new furostanol saponins, named ascalonicoside A1/A2 (1a/1b) and ascalonicoside B (4), respectively, along with compounds 2a and 2b, most likely extraction artifacts. On the basis of 2D NMR and mass spectrometry data, the structures of the novel compounds were elucidated as furost-5(6)-en-3beta,22alpha-diol 1beta-O-beta-D-galactopyranosyl 26-O-[alpha-L-rhamnopyranosyl-(1-->2)-O-beta-D-glucopyranoside] (1a), its epimer at position 22 (1b), and furost-5(6),20(22)-dien-3beta-ol 1beta-O-beta-D-galactopyranosyl 26-O-[alpha-L-rhamnopyranosyl-(1-->2)-O-beta-D-glucopyranoside] (4). This is the first report of furostanol saponins in A. ascalonicum. High concentrations of quercetin, isorhamnetin, and their glycosides were also isolated and described.