Discovery of a Potent and Selective MAO-B Inhibitor From a Donepezil-Linked Chalcone Library With Promising Antiparkinsonian Activity.

A focused library of 19 donepezil-linked chalcones (DLCs) was efficiently synthesised through microwave-assisted Claisen-Schmidt condensation and subsequently profiled for their inhibitory activities against cholinesterases (AChE and BuChE) as well as monoamine oxidases (MAO-A and MAO-B). The DLCs exhibited potent and selective inhibition of MAO-B, with IC50 values ranging from 0.019 to 18.98 μM, whereas activity toward MAO-A was moderate to low (IC50 = 0.81 to > 20 μM). Among the tested DLCs, DLC9 and DLC14 showed the highest MAO-B inhibitory potential with IC50 values of 0.054 ± 0.004 μM and 0.019 ± 0.0015 μM, respectively, and high selectivity indexes (> 370 and > 1052, respectively), whereas DLC12 displayed notable MAO-A inhibition (IC50 = 0.81 ± 0.035 μM). Kinetic and reversibility studies revealed that the selected two lead DLCs (DLC9 and DLC14) acted as mixed-type reversible MAO-B inhibitors, with Kᵢ values of 20.0 ± 2.83 nM and 10.0 ± 2.82 nM, respectively. Furthermore, IC50 values of AChE inhibitory activities ranged from 5.40 to > 40 µM, whereas those of BuChE inhibitory activity range from 4.30 to > 40 µM. DLC6 showed the best AChE inhibitory potential with IC50 values of 5.40 ± 0.29 µM, while DLC13 revealed effective BuChE inhibitory potential with an IC50 value of 4.30 ± 0.89 µM. Molecular docking studies performed on hMAO-A and hMAO-B revealed that DLC14 establishes favourable π-π stacking within the aromatic cage of hMAO-B and maintains complementary hydrophobic contacts along the substrate cavity, whereas DLC6 lacks this key interaction due to steric interference of the ethoxy substituent. Among the three most potent MAO-B inhibitors (DLC2, DLC9, and DLC14), DLC2 exhibited the most favourable microsomal stability with the longest half-life and lowest intrinsic clearance, whereas DLC14 showed comparable metabolic profiles in rat and human liver microsomes. Experimental BBB permeability assays were hindered by compound-membrane interactions; however, in silico predictions indicated satisfactory oral bioavailability and brain penetration for all three candidates. In the MPTP-induced rat model of parkinsonism, the selective MAO-B inhibitor DLC14 and the non-selective inhibitor DLC6 significantly improved motor deficits and behavioural impairments across open field, pole, bar, rotarod, and forced swim tests, with progressive improvements observed up to Day 28. Notably, DLC14 consistently outperformed DLC6 and demonstrated an efficacy profile comparable to that of Selegiline, highlighting its therapeutic potential as an antiparkinsonian agent. These results indicate that DLC14 is potent and selective MAO-B inhibitor and could serve as promising candidate for the treatment of neurodegenerative disorders, such as Parkinson's disease.