Discovery of First Quinoline–Acylguanidine Hybrids as Selective Butyrylcholinesterase Inhibitors: Design, Synthesis, and Molecular Basis

Alzheimer’s disease (DA) remains a major therapeutic challenge, and selective butyrylcholinesterase (BChE) inhibition has emerged as a promising strategy for symptomatic treatment, particularly in advanced stages. Herein, a series of novel quinoline–acylguanidine hybrids was designed through a bioisosteric replacement of acridine–thiosemicarbazones and synthesized via a convergent route combining the Pfitzinger reaction with acylguanidine formation. All derivatives were evaluated against BChE and AChE (acetylcholinesterase), and the 2-phenylquinoline derivative 2c (IC50 = 7.14 µM) was identified as the most potent BChE inhibitor, comparable to donepezil (IC50 = 2.39 µM), with selectivity over AChE. Structure–activity relationships revealed that the 2-phenyl substituent is essential for activity, whereas bulky groups (4-bromophenyl) or replacement with methyl abolished inhibition. Molecular docking showed that active compounds bind within the BChE catalytic anionic site with Trp110, Met465, and Trp458, while inactive analogs undergo a 180° flip of the quinoline scaffold, disrupting key interactions. In silico ADME evaluation indicated a favorable CNS drug-like profile (TPSA < 90 Å2, LogBB > −1, no Lipinski violations, and no predicted P-glycoprotein substrate liability). These findings establish the quinoline–acylguanidine scaffold as a promising new chemotype for the development of selective BChE inhibitors with potential applications in Alzheimer’s disease.