Antiplasmodial and Cytotoxic Triterpenoids from the Bark of the Cameroonian Medicinal Plant Entandrophragma congoënse

Eight new triterpenoids, prototiamins A–G (1–6, 9) and seco-tiaminic acid A (10), were isolated along with four known compounds from the bark of Entandrophragma congoënse. Their structures were elucidated by means of HRMS and different NMR techniques and chemical transformations. Assignments of relative and absolute configurations for the new compounds were achieved using NOESY experiments and by chemical modification including the advanced Mosher’s method. Additionally, the structure and relative configuration of compound 3were confirmed by single-crystal X-ray diffraction analysis. Compounds 1, 3, and 5displayed significant in vitro antiplasmodial activity against the erythrocytic stages of chloroquine-sensitive Plasmodium falciparumstrain NF54. Prototiamin C (3) was the most potent of the compounds isolated, with an IC50value of 0.44 μM. All compounds tested showed low cytotoxicity for the L6 rat skeletal myoblast cell line.