Natural and Semisynthetic Triterpenes from Combretum leprosum Mart. with Antiplasmodial Activity

Malaria is responsible for thousands of deaths each year. Currently, artemisinin combination therapy (ACT) is used as first-choice medication against the disease. However, the emergence of resistant strains prompts the search for alternative compounds. The present study aimed to investigate the antiplasmodial activities of natural triterpenes (compounds 1 and 2), and semisynthetic derivatives 1a, 1b, 1c, and 1d. Antiplasmodial assays were carried out using the SYBR Green technique, whereas cytotoxicity was evaluated by the MTT (3-(4,5-dimethylthiazol2-yl)-2,5-diphenyltetrazolium bromide) method. Hemolytic assays were performed on human erythrocytes. An in silico analysis of the compounds against PfENR (Plasmodium falciparum 2-trans-enoyl-reductase) was carried out by molecular docking. Experiments with 1, and its derivatives against P. falciparum showed that 1a was very similar in terms of biological activity to compound 1 (half maximal inhibitory concentration (IC50) ca. 4 ;AM), whereas 1b, 1c, and 1d had reduced antiplasmodial activities (IC50 between 8-103 ;AM). The selectivity indexes of 1 and 1d for HepG2, and Vero cells were > 10. Docking results partially agreed with the in vitro experiments, with 1 and 1c having the best and worst affinities with PfENR, respectively. In conclusion, the results showed that 1 and 1d may serve as biotechnological tools in the development of antimalarial drugs.