Anthraquinone glycosides from Cassia roxburghii and evaluation of its free radical scavenging activity

The methanolic extract of the leaves of Cassia roxburghii DC., was investigated for its anthraquinone glycosides and antioxidant activity. Two new anthraquinone glycosides named emodin 1-O-β-D-glucopyranosyl-(1 → 2)-glucopyranoside (1) and aloemodin 8-O-β-D-glucopyranosyl-(1 → 6)-glucopyranoside (2) along with aloemodin 8-O-β-D-glucopyranoside (3), emodin (4), aloemodin (5) and one flavonoid, quercetin-3-O-α-L-rhamnopyranoside, were isolated from the leaves of C. roxburghii. Structures of the isolated compounds were established by UV, HRESI-MS, and 1D/2D (1)H/(13)C NMR spectroscopy. The total extract and some isolated compounds were determined against DPPH (2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazinyl radical, for their free radical scavenging activity, the total alcoholic extract showed strong antioxidant activity while the two new compounds showed weak antioxidant activity.