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 IC(50) values of 28.61 and 36.93 microM toward DPPH; respective IC(50) values of 9.79 and 11.40 microM toward ONOO(-). However, compound 2 showed no DPPH scavenging activity and weak ONOO(-) scavenging activity with an IC(50) value of 32.00 microM.