Antioxidative Constituents of the Aerial Parts of Galium spurium

As part of an ongoing search for natural plants with antioxidant compounds by measuring the radical scavenging effect on 1,1-diphenyl- 2-picrylhydrazyl (DPPH), a total extract of the twigs of Galium spurium L. (Rubiaceae) was found to show potent antioxidant activity. Subsequent activity-guided fractionation of the methanolic extract led to the isolation of nine compounds, asperulosidic acid methyl ester (1), asperuloside (2), caffeic acid (3), kaempferol-3-O-L-rhamnopyranoside (4), quercetin-3-O-[alpha-L-rhamnopyranosyl(1 -> 6)-beta-D-glucopyranoside] (5), isorhamnetin-3-O-glucopyranoside (6), quercetin-3-O-alpha-L-rhamnopyranoside (7), kaempferol-3-O-[alpha-L-rhamnopyranosyl(1 -> 6)-beta-D-glucopyranoside] (8), and quercetin (9). Their structures were elucidated by spectroscopic studies. Compounds 1, 3-8 were isolated for the first time from this plant. Among them, compounds 3 and 9 showed the significant radical scavenging effects on DPPH, and compounds 3 and 7 showed the potent riboflavin originated superoxide quenching activities.