Aldoxime- and hydroxy-functionalized chalcones as highly potent and selective monoamine oxidase-B inhibitors

A panel of 30 chalcone derivatives, including 19 aldoxime-chalcone ethers (ACE), and 11 hydroxyl‑chalcones (HC), previously synthesized using a Pd-catalyzed C–O cross-coupling method were evaluated for their inhibitory activities against monoamine oxidases (MAOs), cholinesterases (ChEs), and β-secretase (BACE-1). HC6 was the most potent inhibitor of MAO-B with an IC50 value of 0.0046 µM and a selectivity index (SI) of 1,113. HC3 also potently inhibited MAO-B (IC50 = 0.0067 µM) and had the highest SI (1,455). ACE7 and ACE15 were also potent MAO-B inhibitors (IC50 = 0.012 and 0.018 µM, respectively), with SIs of 260 and 1,161, respectively. HC3 and HC6 were reversible competitive inhibitors of MAO-B, with Ki values of 0.0036 and 0.0013 μM, respectively. A structure–activity relationship revealed that methyl and fluorine substituents contributed to increasing both inhibition and selectivity. ACE7 was the most effective inhibitor of MAO-A (IC50 = 1.49 µM), followed by ACE3 (IC50 = 3.75 µM). No compounds effectively inhibited AChE, BChE, or BACE-1. A docking simulation showed that the ligand efficiency and docking scores of HC3 and HC6 toward MAO-B were consistent with the experimental IC50 values. These results suggest that HC3 and HC6 can be considered promising candidates for the treatment of neurological disorders.