In vitro anti-inflammatory activity of 3-O-methyl-flavones isolated from Siegesbeckia glabrescens.

Four flavones, 3,4'-O-dimethylquercetin (1), 3,7-O-dimethylquercetin (2), 3-O-methylquercetin (3) and 3,7,4'-O-trimethylquercetin (4) were isolated as the inhibitors of nitric oxide production in activated microglia (IC(50) values: 11.1, 4.2, 3.8, and 25.1 microM, respectively). They suppressed the expression of protein and mRNA of inducible nitric oxide synthase. Furthermore, compounds 2 and 3 showed scavenging activity of peroxynitrite with SC(50) values of 1.75 and 0.77 microM, respectively.