Synthesis, Pharmacological Evaluation, and Molecular Modeling of Phthalimide Derivatives as Monoamine Oxidase and Cholinesterase Dual Inhibitors

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by dementia and cognitive decline, associated with synaptic loss and degeneration of cholinergic neurons. New multitarget inhibitors for monoamine oxidase (MAO) and cholinesterase (ChE) enzymes are emerging as a potential treatment strategy for AD. Herein, we synthesized a series of N-benzyl-substituted biaryl phthalimide derivatives (3a-3m) encompassing potentially therapeutically active arenes/heteroarenes to serve as multitarget compounds for treating AD. To improve their binding affinity as well as inhibitory activity against ChE and MAO target proteins, comparable molecular structures were synthesized bearing electron-donating, electron-withdrawing, heterocyclic, and fluorinated moieties for a comprehensive SAR. In vitro evaluation of synthesized compounds against cholinesterases (AChE/BChE) and monoamine oxidases (MAO-A/MAO-B) revealed that compound 3e had good potency against AChE (IC₅₀ = 0.24 μM) and BChE (IC₅₀ = 6.29 μM), while compound 3f had the highest inhibition of MAO-B (IC₅₀ = 0.09 μM). Selected compounds (3e,f) showed no cytotoxicity against the neuroblastoma cell line (SH-SY5Y) and normal human embryonic HEK-293 cells. Moreover, they showed high blood-brain barrier penetration (PAMPA assay) and reversible MAO-B inhibitory activity (ex vivo). In molecular docking studies, compounds 3e and 3f displayed the highest binding affinity with ChEs and MAO-B, respectively. In silico ADMET studies and MD simulation studies were also carried out for the most potent derivatives (3e and 3f), suggesting their strong potential as anti-Alzheimer agents.