Design, Synthesis, and Biological Evaluation of Chiral Urea and Thiourea Derivatives as Multitarget-Directed Anti-Alzheimer Agents

A series of novel chiral urea and thiourea compounds were designed as multitarget-directed ligands for Alzheimer's disease and evaluated against hAChE, hBChE, and hMAO-B, with exploratory assessment of HSD10. These chiral compounds were synthesized and fully characterized, and their enantiopurity was confirmed via HPLC. Biological screening revealed that several of the 38 single-enantiomer derivatives exhibited potent triple inhibition of hAChE, hBChE, and hMAO-B. Biological screening revealed that a significant number of the 38 synthesized single-enantiomer urea and thiourea derivatives potent inhibition across the primary target panel. Among them, compounds 14 S (hAChE: 0.08 mu M, hBChE: 0.93 mu M, hMAO-B: 0.02 mu M), 23 R (hAChE: 0.06 mu M, hBChE: 0.74 mu M, hMAO-B: 0.08 mu M), 6 S (hAChE: 0.08 mu M, hBChE: 0.65 mu M, hMAO-B: 0.08 mu M), and 30 S (hAChE: 0.04 mu M, hBChE: 0.74 mu M, hMAO-B: 0.19 mu M) showed the most promising multitarget profiles. Compounds 6 S and 23 R also displayed anti-A beta aggregation activity, whereas 12 S combined dual hMAO-B/hAChE inhibition with antioxidant activity. Compounds 3 R and 11 R were found to be highly active against hMAO-B (0.03 mu M and 0.06 mu M, respectively) and hBChE (0.68 and 0.72 mu M). HSD10 inhibition was limited overall, with only compound 26 S showing moderate activity (52.2%) at higher micromolar concentration. Molecular docking and molecular dynamics simulations supported the proposed ligand-target interactions for the most active compounds. In addition, selected derivatives showed no acute cytotoxicity under the tested conditions in HepG2 cells and high permeability potential in the PAMPA-BBB assay. Based on their in vitro profiles, seven compounds (3 R, 6 S, 11 R, 12 S, 14 S, 23 R, and 30 S) were advanced to in vivo evaluation, and compounds 6 S, 12 S, and 23 R, 30 S produced significant improvements in the Morris Water Maze model. Collectively, these findings identify chiral urea and thiourea derivatives as promising lead structures for further anti-Alzheimer drug discovery.