Synthesis, Cytotoxicity, and Leishmanicidal Evaluation of Ent-beyerene and Ent-kaurene Derivatives

Cutaneous leishmaniasis (CL) is an infectious disease endemic of tropical and subtropical countries, for which current pharmacologic treatments have serious drawbacks. Therefore, new and improved medical treatments are required. On the other side, natural products have been a valuable source of bioactive molecules, but unlike other products of natural origin, diterpenoids are molecules with only a few studies as antiparasitic drugs. Continuing our work on syntheses of beyerenes, and focusing on obtaining more compounds with antiparasitic activity, we describe in this work the syntheses and activity of several ent-beyerene and ent-kaurene type of compounds against CL, and also their toxicity. Utilizing classical reactions such as Grignard, Mitsunobu, and Williamson, among others, it was possible to modify rings A and D of ent-beyerenes, specifically C-19 on ring A, and C-15 and C-16 on ring D. A total of 40 new compounds were obtained, 21 of them being active against Leishmania (Viannia) braziliensis with median effective concentration (EC50) values less than 25.0 mu g/mL and of these with EC50 values ranging from 1.8 to 7.1 mu g/mL and Selectivity Index (SI) varying from 1.1 to 5.1. All compounds showed to be highly cytotoxic at concentrations less than 100 mu g/mL, except compound 37 that was cytotoxic at 279.7 mu g/mL and moderately active against L. braziliensis (EC50=33.5 mu g/mL and an SI of 8.4. All active compounds were ent-beyerene type.