In Vitro antileishmanial evaluation, molecular docking, dynamics simulations, and DFT Studies of tetrahydropyridine...

Leishmaniasis, a neglected tropical disease caused by Leishmania parasites, lacks safe and effective treatments due to drug resistance and toxicity. This study introduces novel tetrahydropyridine (THP) derivatives as potential inhibitors of trypanothione reductase (TR), a unique redox enzyme essential for parasite survival. Eight THP analogs were synthesized and screened for antileishmanial activity against Leishmania major promastigotes (strain MRHO/IR/75/ER) using the MTT assay, revealing compound A5 as the most potent (IC₅₀ = 89.2 ± 4.5 nM) with favorable selectivity over J774 macrophages. Structure-activity relationship analysis highlighted the role of electron-withdrawing substituents (e.g., Cl at R₁) in enhancing potency, while bulky or highly polar groups (e.g., NO₂ at R₂ in A7) diminished efficacy. Molecular docking against L. infantum TR (PDB: 6T95) demonstrated strong binding affinities for active compounds, with A5 forming key π-π stacking interactions (Trp21, Tyr110) and π-sulfur interactions (Met113). Stability was confirmed via 100-ns molecular dynamics simulations, showing low RMSD and RMSF values and persistent interactions. Density functional theory (DFT) calculations at the B3LYP/6-31 + G(d, p) level correlated electronic descriptors (e.g., wider HOMO-LUMO gap and higher hardness in A5) with superior biological activity, docking scores, and ADME (Absorption, Distribution, Metabolism, and Excretion) profiles. In silico pharmacokinetic predictions indicated good oral absorption and low blood-brain barrier penetration, supporting drug-likeness. Overall, this integrated phenotypic and computational approach identifies THP scaffolds, particularly A5, as promising leads for developing orally bioavailable antileishmanial agents targeting TR, paving the way for further optimization and in vivo validation.