In vitro schistosomicidal activity of the crude extract, fractions and Primin, the major active benzoquinone constituent from the leaves of Miconia willdenowii (Melastomaceae)

Eight native plant extracts from the Brazilian Atlantic Forest, Acacia polyphylla, Allophylus racemosus, Casearia arborea, Duguetia lanceolata, Metrodorea stipularis, Trichilia emarginata, Miconia willdenowii, Mollinedia widgrenii, were screened for potential schistosomicidal activity. The crude ethanolic extract of Miconia willdenowii (at a concentration of 200 μg/mL) showed the most promising results, killing approximately 65% of the  Schistossoma mansoni worms, in comparison to praziquantel. This extract was then submitted to a bioguided-phytochemical study. After liquid-liquid partition was performed, the hexane subfraction disclosed the most significant schistosomicidal activity of 80% against the adult worms at a concentration of 75 μg/mL and 25% at 50 μg/mL. Purification of this active subfraction led to the isolation of 2-methoxy-6-pentyl-benzoquinone (1, also known as Primin) as the active metabolite responsible for the observed schistosomicidal effect (IC50 = 7.08 μg/mL). The schistosomicidal effect of M. willdenowii and Primin is the first time in which such a result has been reported.