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

<p>From the butanolic and the ethyl acetate extracts of <i>Rhamnus alaternus</i> 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-α-L-rhamnopyranoside (<b>1</b>); 1,2,6,8 tetrahydroxy-3 methyl anthraquinone 8-O-ß-D-glucopyranoside <b>(2</b>) and 1, 6 dihydroxy-3 methyl 6 [2′-Me (heptoxy)] anthraquinone <b>(3</b>)) were isolated and elucidated together with the two known anthraquinone glycosides, Physcion-8-O-rutinoside (<b>4</b>) and emodin-6-O-α-L-rhamnoside (<b>5)</b> as well as with the known kaempferol-7-methylether (<b>6</b>), β-sitosterol (<b>7</b>) and β-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 (<b>3</b>), (<b>4</b>) and (<b>6</b>) showed the highest activity with IC₅₀ values of 9.46, 27.68 and 2.35 μg/mL, respectively.