Design, Synthesis, Pharmacological Activities, Structure–Activity Relationship, and In Silico Studies of Novel 5-Substituted-2-(morpholinoimino)-thiazolidin-4-ones

[Image: see text] This study is aimed to synthesize morpholine- and thiazolidine-based novel 5-(substituted)benzylidene)-2-(morpholinoimino)-3-phenylthiazolidin-4-ones (3–26) and characterized by molecular spectroscopy. The synthesized compounds were subjected to antioxidant activity with anticholinesterase, tyrosinase, and urease inhibition activities and evaluated the structure–activity relationship (SAR) of enzyme inhibition activities. Compound 11 was found to be the most active antioxidant. In anticholinesterase inhibition, compound 12 (IC(50): 17.41 ± 0.22 μM) was the most active against AChE, while compounds 3–26 ( except 3, 8, and 17) showed notable activity against BChE. Compounds 17 (IC(50): 3.22 ± 0.70 mM), 15 (IC(50): 5.19 ± 0.03 mM), 24 (IC(50): 7.21 ± 0.27 mM), 23 (IC(50): 8.05 ± 0.11 mM), 14 (IC(50): 8.10 ± 0.22 mM), 25 (IC(50): 8.40 ± 0.64 mM), 26 (IC(50): 8.76 ± 0.90 mM), and 22 (IC(50): 9.13 ± 0.55 mM) produced higher tyrosinase inhibition activity. In urease inhibition activity, compounds 20 (IC(50): 16.79 ± 0.19 μM), 19 (IC(50): 18.25 ± 0.50 μM), 18 (IC(50): 20.24 ± 0.77 μM), 26 (IC(50): 21.51 ± 0.44 μM), 25 (IC(50): 21.70 ± 0.06 μM), and 24 (IC(50): 22.49 ± 0.11 μM) demonstrated excellent activities. Besides, the molecular docking study was applied to better understand the inhibitory mechanism between (1–26) compounds and enzymes at the molecular level. According to the results of this study, the synthesized compounds exhibited a better binding affinity toward these enzymes compared to the positive control. Further, molecular mechanics Poisson–Boltzmann surface area (MM/PBSA) binding free energy and molecular dynamics (MD) simulation analyses were performed for AChE with compound 26, which showed high inhibitory activity in silico and in vitro studies. In conclusion, novel morpholine and thiazolidine-based derivative compounds may be pharmacologically effective agents for AChE, BChE, tyrosinase, and urease enzymes.