Isolation and identification of new anthraquinones from Rhamnus alaternus L and evaluation of their free radical scavenging activity

From the butanolic and the ethyl acetate extracts of Rhamnus alaternus L root bark and leaves, three new anthraquinone glycosides, alaternosides A-C (1,4,6,8 tetrahydroxy-3 methyl anthraquinone 1-O-ss-D-glucopyranosyl-4,6-di-O-alpha-L-rhamnopyranoside (1); 1,2,6,8 tetrahydroxy-3 methyl anthraquinone 8-O-ss-D-glucopyranoside (2) and 1, 6 dihydroxy-3 methyl 6 [2 `-Me (heptoxy)] anthraquinone (3)) were isolated and elucidated together with the two known anthraquinone glycosides, Physcion-8-O-rutinoside (4) and emodin-6-O-alpha-L-rhamnoside (5) as well as with the known kaempferol-7-methylether (6), beta-sitosterol (7) and beta-sitosterol-3-O-glycoside (8). Their chemical structures were elucidated using spectroscopic methods (1D-, 2D-NMR and FAB-MS). Free radical scavenging activity of the isolated compounds was evaluated by their ability to scavenge DPPH. free radicals. Compounds (3), (4) and (6) showed the highest activity with IC50 values of 9.46, 27.68 and 2.35 mu g/mL, respectively.