Design, synthesis, and biological evaluation of kenpaullone derivatives as potential dual inhibitors of cholinesterases and glycogen synthase kinase-3β.

Alzheimer's disease (AD) is a multifaceted neurodegenerative disorder that demands therapeutic approaches targeting multiple pathological pathways. Among these, the cholinergic deficit, amyloid-β (Aβ) aggregation, and tau hyperphosphorylation are recognized as key contributors to disease progression. This study aimed to develop multitarget-directed ligands (MTDLs) by rationally modifying the potent but poorly soluble glycogen synthase kinase 3β (GSK-3β) inhibitor, kenpaullone 17b, to simultaneously inhibit cholinesterases (ChEs) and GSK-3β while improving physicochemical properties. Initial substitution of the C9-bromo group in 17b with a sulfonamide moiety produced compound 17m, which retained strong GSK-3β inhibition (IC₅₀ = 0.35 μM) and acquired modest acetylcholinesterase (AChE) inhibitory activity (IC₅₀ = 20 μM). Further elongation of the C9 substituent with a cyclohexylaminopropyl chain yielded compound 18o, exhibiting balanced dual inhibition of AChE (IC₅₀ = 1.7 μM), butyrylcholinesterase (BChE) (IC₅₀ = 5.3 μM), and GSK-3β (IC₅₀ = 5.7 μM). Compound 18o also inhibited Aβ1-42 self-aggregation by 21 % at 10 μM and demonstrated blood-brain barrier (BBB) permeability with a 100-fold improvement in aqueous solubility compared with 17b. Molecular docking and molecular dynamics simulations revealed stable dual binding conformations within the AChE and GSK-3β active sites, supported by key hydrogen bonds and hydrophobic interactions. Overall, the structurally flexible analog 18o represents a promising dual ChE/GSK-3β inhibitor with improved drug-like characteristics, warranting further preclinical evaluation as a potential therapeutic lead for AD.