Eugenol-based carbazole-triazole derivative 5m exhibits potent anti-plasmodial activity associated with predicted plasmepsin II binding and oxidative stress in chloroquine-resistant Plasmodium falciparum.

Malaria continues to be a significant health concern due to the resistance of Plasmodium species to existing drugs, highlighting the urgent need for new antimalarials. In our previous study, the eugenol-based carbazole-triazole derivative 5m was identified as a promising anti-plasmodial lead against the chloroquine-sensitive NF-54 strain. However, its activity against CQ-resistant parasites and its underlying mechanism of action remained unexplored. Therefore, the present study investigated the anti-plasmodial activity of compound 5m against both CQ-sensitive (3D7) and CQ-resistant (K1) strains of Plasmodium falciparum and elucidated its mechanism of action. Compound 5m exhibited potent anti-plasmodial activity (IC₅₀ < 5 μM) against both parasite strains. Molecular docking and molecular dynamics simulations suggested that Plasmepsin II may be a potential molecular target for compound 5m. Compound 5m also demonstrated an additive interaction with chloroquine. Interestingly, Derivative 5m reduced metabolic activity and increased reactive oxygen species (ROS) in a dose-dependent manner. Additionally, treatment with 5m, both alone and in combination with CQ, elevated ROS levels measured by the DCFH-DA fluorescence assay in drug-resistant parasites. Further, 5m was found to affect DNA damage, and increased phosphatidylserine externalization was observed. Derivative 5m was non-cytotoxic to Vero cells and exhibited favourable ADMET properties. Collectively, our findings substantially expand the pharmacological evaluation of compound 5m by demonstrating its activity against drug-resistant P. falciparum and providing mechanistic evidence supporting anti-plasmodial action.