Discovery of potent and selective MAO-B inhibitors from a morpholine-substituted chalcone library for...

A series of targeted chalcones (TCs) was designed and synthesised using a microwave-assisted synthetic method to introduce diverse substituents at different positions on the phenyl ring. The structures of all nineteen TC analogues were confirmed by NMR, FTIR, and HRMS. In vitro tests against acetyl- and butyrylcholinesterases (AChE and BuChE), β-Site Amyloid Precursor Protein Cleaving Enzyme 1 (BACE1), and monoamine oxidases (MAO-A and MAO-B) showed that MAO-B was the most potent and selective. Among them, TC12 was the strongest inhibitor (IC₅₀ = 11.00 ± 1.0 nM; SI > 3636) and worked competitively (K_i = 7.16 ± 1.20 nM). In terms of IC₅₀ = 50.0 ± 1.0 nM and SI > 800, TC9 was ranked second. TC12 showed no time-dependent inhibition of MAO-B, and its MAO-B inhibition was reversible. Molecular docking studies revealed that TC12 establishes favourable interactions within the MAO-B active site, particularly through π-π stacking with aromatic cage residues (TYR398 and TYR435), while showing limited engagement with key regions of MAO-A. ADME predictions indicated that TC12 exhibits favourable drug-like properties, including compliance with Lipinski's rules, moderate CNS permeability, and a pharmacokinetic profile supportive of oral bioavailability. In vitro Parallel Artificial Membrane Permeability Assay (PAMPA) and microsomal stability studies revealed that TC9 exhibited high blood-brain barrier (BBB) permeability comparable to carbamazepine, while TC12 showed moderate permeability but was consistent with its predicted CNS penetration. Both TC analogues demonstrated favourable metabolic stability profiles in rat and human liver microsomes, supporting their potential for further pharmacological evaluation. Overall, TC12 represents a promising candidate for selective MAO-B inhibition.