Geranylbenzoquinonoids from Lettowianthus stellatus fruits.

The geranylbenzoquinonoids 7-(3,7-dimethylocta-2,6-dienyl)-5-hydroxy-3H-benzofuran-2-one (lettowienolide), dimethyl 2,3-bis-[5-(3,7-dimethylocta-2,6-dienyl)-3,6-dioxocyclohexa-1,4-dienyl]-succinate (lettowiquinone), 2-(3,7-dimethylocta-2,6-dienyl)-6-[7-(3,7-dimethylocta-2,6-dienyl)-5-hydroxybenzofuran-2-yl]-[1,4]benzoquinone (lettowifuraquinone), methyl [3-(3,7-dimethylocta-2,6-dienyl)-6-methyl-5-(3-methylbut-2-enyl)-1,4-dioxo-1,5, 8,8a-tetrahydro-4H-nathphalen-4a-yl)]-acetate (lettowinone) and methyl [6-hydroxy-2-methyl-2-(4-methylpent-3-enyl)-2H-chromen-8-yl]-acetate (lettowipyraquinol) were isolated from fruits of Lettowianthus stellatus Diels, together with juvenile hormone III and 7-octadecen-9-ynoic acid. Lettowienolide and lettowiquinone exhibited mild in vitro activity against the Plasmodium falciparum malaria parasite (each IC(50) approximately 20 microg mL(-1)). Structural determination was achieved based on extensive analysis of spectroscopic data.