Kaempferol glycosides with antioxidant activity from Brassica juncea

From the leaves of Brassica juncea, three kaempferol glycosides, kaempferol-3-O-(2-O-sinapoyl)-β-d-glucopyranosyl-(1→2) -β-d-glucopyranoside-7-O-β-d-glucopyranoside (1), kaempferol-3-O- β-d-glucopyranosyl-(1→2)-β-d-glucopyranoside-7-O-β-d- glucopyranosyl-(1→6)-β-d-glucopyranoside (2), and kaempferol-3-O-(2-O- sinapoyl)-β-d-glucopyranosyl-(1→2)-β-d-glucopyranoside-7-O- β-d-glucopyranosyl-(1→6)-β-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 μM toward DPPH; respective IC₅₀ values of 9.79 and 11.40 μM toward ONOO ^-. However, compound 2 showed no DPPH scavenging activity and weak ONOO^- scavenging activity with an IC₅₀ value of 32.00 μM.