Design and synthesis of Thiazole-derived α,β-unsaturated ketones as potential antimalarial agents: integrated biophysical and computational insights into putative PfLDH targeting.

A focused series of thiazole-derived α,β-unsaturated ketones (DRS6-10) was rationally designed and synthesized using ethyl 2-(3-formyl-4-hydroxyphenyl)-4-methylthiazole-5-carboxylate as the key precursor. The synthesized analogues were structurally characterized by FTIR, NMR, and ESI-MS spectroscopy. The compounds were evaluated for in vitro antiplasmodial activity against the chloroquine-sensitive Plasmodium falciparum 3D7 strain, exhibiting IC₅₀ values in the range of 1.02-1.62 μM (0.64-1.02 μg·mL-1). Among them, DRS8 emerged as the most active analogue, demonstrating approximately 0.39-fold potency relative to quinine under identical experimental conditions. In addition, DRS8 displayed notable antioxidant activity in the DPPH assay (IC₅₀ = 18.4 μg·mL-1), suggesting potential redox-modulating capability. Isothermal titration calorimetry (ITC) revealed favorable binding of DRS8 to Plasmodium falciparum lactate dehydrogenase (PfLDH), characterized by an enthalpy-driven interaction profile (ΔH ≈ -6.5 kcal·mol-1; Kd = 0.42 μM). Complementary molecular docking and 500 ns molecular dynamics simulations indicated stable accommodation of DRS8 within the PfLDH active site, supported by hydrogen bonding and π-interactions with key residues, including Asp342, Arg60, and Thr66. MM-GBSA analysis suggested a favorable relative binding energy (ΔGbind = -44.6 kcal·mol-1), consistent with strong ligand-protein interactions, although such values are interpreted qualitatively due to known methodological limitations. WaterMap analysis further indicated displacement of high-energy hydration sites (ΔGhydration ≈ -7.8 kcal·mol-1), which may contribute to binding affinity and entropy gain. Overall, these integrated experimental and computational findings identify DRS8 as a promising thiazole-based antiplasmodial scaffold and support PfLDH as a putative molecular target. Further studies involving direct enzymatic assays and cytotoxicity evaluation are warranted to validate target specificity and therapeutic potential.