Background: Thymol, a natural phenol with antimicrobial and antioxidant activities, and its derivatives offer promising scaffolds for antimalarial drug development, potentially helping overcome resistance. Materials and Methods: In this study, thymol derivatives were synthesized and assessed as antiplasmodial agents against both resistant and sensitive strains of P. falciparum, as well as Plasmodium knowlesi. The ligand molecules were assessed with Plasmodium falciparum chloroquine resistance transporter (PfCRT)’s potential using in silico molecular docking and ADMET analysis. The parent compound, thymol, was chemically modified through esterification and conjugation with hydroxybenzoic acid and cinnamic acid derivatives to generate analogs with varied substitution patterns. Results: The findings showed that among seven successfully synthesized thymol derivatives, compounds 4 and 6 exhibited notable potency against Plasmodium falciparum 3D7 (EC₅₀ = 6.01 ± 1.7 µM and 6.8 ± 1.1 µM, respectively) with high SI values (16.5 and 14.6, respectively), indicating improved selectivity relative to thymol. The cytotoxicity evaluation against HCF mammalian cells revealed that most thymol derivatives were non-toxic, with CC₅₀ values greater than 99 µM, except for compound 3 (CC₅₀ = 71.4 ± 4.5 µM) and compound 1 (CC₅₀ = 58.4 ± 2.3 µM), which exhibited moderate cytotoxic effects. The molecular docking results showed that compounds 3 (−8.4 kcal/mol), 4 (−8.3 kcal/mol), and 6 (−8.3 kcal/mol) exhibited strong binding affinities toward the PfCRT protein. Conclusions: Therefore, thymol derivative compounds 4 and 6 exhibited stronger antiplasmodial activity in vitro against P. falciparum and P. knowlesi with safety profiles against mammalian cells, targeting PfCRT, highlighting their potential as lead antimalarial candidates.

Ten carvacrol conjugates with hydroxybenzoic/cinnamic acid have been synthesized and evaluated for their antiplasmodial activity against Plasmodium falciparum 3D7, K1, and A1H1 strains. Most of the hybrids demonstrated superior activity relative to the parent compounds, with compounds 1, 6, 9, and 10 exhibiting the highest potency against P. falciparum 3D7 (EC50 = 6.6–7.5 μM). Compounds 1, 6, and 9 exhibited lower cytotoxicity against H9c2 cells. However, the selectivity index (SI) of compound 10 is less than 10, indicating moderate cytotoxicity and selectivity. The derivatives were generally more active against the drug-sensitive 3D7 strain than against the resistant K1 and A1H1 strains. Based on molecular docking and molecular dynamics simulations, the active hybrids were predicted to interact favorably with the Plasmepsin II binding site, consistent with the significant correlation observed between antiplasmodial activity and docking scores. Molecular descriptor analysis and PLS-based QSAR modelling indicated that antiplasmodial activity was influenced by a combination of electronic, steric, and physicochemical properties, with TPSA and HOMO energy showing significant correlations with biological activity. In silico ADMET prediction suggested generally acceptable drug-likeness and pharmacokinetic profiles for the active derivatives. Overall, the results indicated that compounds 1, 6, 9, and 10 as promising scaffolds for further antiplasmodial drug development.