A series of new thiosemicarbazones derived from natural diterpene kaurenoic acid were synthesized and tested against the epimastigote forms of Trypanosoma cruzi to evaluate their antitrypanosomal potential. Seven of the synthesized thiosemicarbazones were more active than kaurenoic acid with IC 50 values between 2-24.0 µM. The o-nitrobenzaldehyde-thiosemicarbazone derivative was the most active compound with IC 50 of 2.0 µM. The results show that the structural modifications accomplished enhanced the antitrypanosomal activity of these compounds. Besides, the thiocyanate, thiosemicarbazide and the p-methyl, p-methoxy, p-dimethylamine, m-nitro and o-chlorobenzaldehydethiosemicarbazone derivatives displayed lower toxicity for LLMCK 2 cells than kaurenoic acid, exhibing an IC 50 of 59.5 µM. OPEN ACCESSMolecules 2011, 16 1167

RESUMO: "Avaliação das atividades moluscicida e cercaricida (Schistosoma mansoni) dos extratos de Croton floribundus e do ácido caurenóico". Extratos de Croton fluribundus (Euphorbiaceae), ácido caurenóico e dois derivados do ácido caurenóico foram avaliados como moluscicida, cercaricida e também foi verificada a letalidade destas amostras frente a larvas de Artemia salina Leach. Nestes ensaios foram observadas significantes atividades moluscicida e cercaricida associadas a uma reduzida toxicidade frente ao camarão de água salgada. Unitermos: Biomphalaria glabrata, Croton floribundus, Artemia salina, ácido caurenóico, Schistosoma mansoni, cercárias.ABSTRACT: Lethality of the extracts of Croton floribundus (Euphorbiaceae), a medicinal plant from south Brazil, and of the kaurenoic acid, an isolated compound, and two of its derivatives against adult Biomphalaria glabrata snails, Schistosoma mansoni cercariae and Artemia salina Leach. brine shrimp larvae are reported. Both extracts and the isolated compound showed significant molluscicidal and cercaricidal activities and reduced toxicity in brine shrimp assays.