5-Methylflavasperone and rhamnetin from Guiera senegalensis and their antioxidative and 5-lipoxygenase inhibitory activity.

From the methylene chloride extract of the leaves of Guiera senegalensis a novel naphthopyran, 5-methylflavasperone (5,8,10-trimethoxy-2-methyl-4 H-naphtho[1,2-b]pyran-4-one), as well as rhamnetin were isolated. Rhamnetin showed a strong inhibitory activity on 5-lipoxygenase from porcine leucocytes with an IC50 value of 0.7 microM whereas 5-methylflavasperone revealed only a weak inhibitory activity (IC50 > 200 microM). In the deoxyribose assay both compounds exerted similar antiradicalar effects (IC50 15.8 and 16.7 microM, respectively). In another assay only rhamnetin inhibited peroxidation of phospholipid liposomes (IC50 = 2.4 microM). For 5-methylflavasperone no dose dependent inhibition could be observed.