Kaempferol Glycosides with Antioxidant Activity from Brassica juncea

From the leaves of Brassica juncea, three kaempferol glycosides, kaempferol-3-O-(2-O-sinapoyl)-beta-D-glucopyranosyl-(1 -> 2)-beta-D-glucopyranoside-7-O-beta-D-glucopyranoside (1), kaempferol-3-O-beta-D-glucopyranosyl-(1 -> 2)-beta-D-glucopyranoside-7-O-beta-D-glucopyranosyl-(1 -> 6)-beta-D-glucopyranoside (2), and kaempferol-3-O-(2-O-sinapoyl)-beta-D-glucopyranosyl-(1 -> 2)-beta-D-glucopyranoside-7-O-beta-D-glucopyranosyl-(1 -> 6)-beta-D-glucopyranoside (3) were isolated and the structures elucidated on the basis of spectral and chemical evidences. Antioxidant activities were determined by measuring the scavenging activities on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and peroxynitrite (ONOO-). Compounds 1 and 3 showed good antioxidant activities with respective IC50 values of 28.61 and 36.93 mu M toward DPPH; respective IC50 values of 9.79 and 11.40 mu M toward ONOO-. However, compound 2 showed no DPPH scavenging activity and weak ONOO- scavenging activity with an IC50 value of 32.00 mu M.