Eleganolone, a Diterpene from the French Marine Alga Bifurcaria bifurcata Inhibits Growth of the Human Pathogens Trypanosoma brucei and Plasmodium falciparum

Organic extracts of 20 species of French seaweed have been screened againstTrypanosoma brucei rhodesiensetrypomastigotes, the parasite responsible for sleepingsickness. These extracts have previously shown potent antiprotozoal activitiesin vitroagainstPlasmodium falciparumandLeishmania donovani. The selectivity of the extractswas also evaluated by testing cytotoxicity on a mammalian L6 cell line. The ethylacetateextract of the brown seaweed,Bifurcaria bifurcata,showed strong trypanocidal activitywith a mild selectivity index (IC50= 0.53 μg/mL;selectivity index (SI)= 11.6). Bio-guidedfractionation led to the isolation of eleganolone, the main diterpenoid isolated from thisspecies. Eleganolone contributes only mildly to the trypanocidal activity of the ethylacetate extract (IC50= 45.0 μM, SI = 4.0). However,a selective activity againstP. falciparumerythrocytic stagesin vitrohas been highlighted (IC50= 7.9 μM, SI = 21.6).