Targeting Blood-Stage Malaria: Design, Synthesis, Characterization, In Vitro, and In Silico Evaluation of Pyrrolidinodiazenyl Chalcones

Malaria is a pervasive and deadly threat to the global population, and the resources available to treat this disease are limited. There is widespread clinical resistance to the most commonly prescribed antimalarial drugs. To address this issue, we synthesized a range of 4′-pyrrolidinodiazenyl chalcones using a covalent bitherapy approach to study their potential antimalarial properties. We examined the structure–activity relationships of these compounds, which could explain their antimalarial activities. The in vitro blood stage antimalarial activity of the compounds was evaluated against the mixed-blood stage culture (ring, trophozoites and schizonts) of Plasmodium falciparum 3D7, and the 50% inhibitory concentrations (IC₅₀s) ranged from 3.3 to 22.2 μg/mL after 48 h of exposure. Compounds 11, 19, and 22 displayed pronounced IC₅₀ values of 7.6 μg/mL, 6.4 μg/mL, and 3.3 μg/mL, respectively. The in vitro cytotoxicity of the active compounds was evaluated on human-derived Mo7e cells and murine-derived BA/F3 cells. Compounds 11 and 19 were found to be noncytotoxic (> 40 μg/mL), whereas compound 22 displayed cytotoxicity at higher concentrations. Moreover, these compounds exerted negligible hemolytic effects on human RBCs at their active concentrations. Molecular docking of these compounds revealed good hydrophobic and hydrogen bonding interactions with the binding sites of Plasmodium falciparum-dihydrofolate reductase, providing a rationale for their antimalarial activity, which is consistent with the in vitro results.