MW Assisted Synthesis of New 4,6-diaryl-3,4-Didhydropyrimidines-2(1H)-thione Derivatives: Tyrosinase Inhibition, Antioxidant, and Molecular Docking Studies

A number of new methoxy-substituted 4,6-diaryl-3,4-dihydropyrimidine-2(1H)-thiones (DH-Pyr-S, 17-28) were designed and synthesized by the reaction of methoxy-substituted chalcones (1–14) with thiourea using solid-phase microwave method (MW) in view of the structural requirements as suggested in the pharmacophore model for tyrosinase inhibition (TI). Synthesized compounds were assessed for their in vitro TI potential and compounds 16, 17, and 21 exhibited notable tyrosinase inhibitory properties at the concentrations of 31.86 ± 2.45 µM, 44.58 ± 0.46 µM, and 48.47 ± 0.66 µM, respectively. Compounds (16, 17, and 21) were exhibited experimentally more potent TI than the standard used in terms of the IC50 value (Kojic acid, 55.38 ± 2.30 µM; p<0.0001). Additionally, DPPH activity of 15-28 were evaluated and compound 17 showed the moderate DPPH activity (45.64 ± 0.34%). Binding affinities of synthesized molecules to the tyrosinase catalytic core were further investigated through in silico molecular docking studies using AutoDock Vina (version 1.2.5), discovery studio accelyrs (BIOVIA, Dassault Systèmes) and predicting small-molecule pharmacokinetic properties using graph-based signatures (pkCSM) programs were used for ADMET calculations. Among synthesized compounds 15, 21, and 24 revealed high binding affinity to tyrosinase active site with lowest binding free energy (ΔG) values of -7.9 kcal/mol, thereby outperformed kojic acid affinity. In conclusion most modeling results were in agreement with their experimental data, suggesting the TI potential of lead compounds.