Identification of Indole-Based Chalcones: Discovery of a Potent, Selective, and Reversible Class of MAO-B Inhibitors

Discovery of potent and reversible MAO-B inhibitors as furanochalcones

A series of twelve furanochalcones (F1-F12) was synthesized and investigated for their human monoamine oxidase inhibitory activities. Among the series, compound (2E, 4E)-1-(furan-2-yl)-5-phenylpenta-2, 4-dien-1-one (F1), which was analyzed by single-crystal X-ray diffraction, showed potent and selective MAO-B inhibitory activity with an inhibition constant (K_i) value of 0.0041 μM and selectivity index of (SI) 172.4, and exhibited competitive inhibition. Introduction of a cinnamyl group to the furanochalcone significantly increased the inhibitory activity. In the dilution-recovery experiments, the residual activities of MAO-A and MAO-B by F1 under the diluted condition fully recovered as compared with the undiluted condition, indicating F1 is a reversible inhibitor. The K_i value of F1 is the lowest among the values of chalcone derivatives and furthermore lower than that (0.0079 μM) of the reversible MAO-B inhibitor, lazabemide, a marketed drug. Molecular docking study against hMAO-B provided the binding site interactions of the lead compound, including strong π-π stacking between the phenyl system and FAD nucleus.

Activation of Nrf2-driven antioxidant enzymes by cardamonin confers neuroprotection of PC12 cells against oxidative damage

Oxidative stress represents a disorder of the redox equilibrium between the production of free radicals and the capability of cells to eliminate them. As subversion of this redox balance is thought to initiate various diseases, living cells maintain a redox equilibrium diligently. More and more pieces of evidence show that oxidative stress has already become a common risk factor in the pathogenesis of neurodegenerative disorders. So, considerable importance has been given to the prevention of oxidative stress as a potential therapeutic strategy. It is well known that the Nrf2-ARE pathway represents one of the most important cellular endogenous defense mechanisms against oxidative stress. Activation of Nrf2 signaling induces the transcriptional regulation of multiple ARE-dependent antioxidant defense genes. Here, we showed that cardamonin (CD), a chalcone isolated from Alpinia katsumadai, attenuated cell death induced by hydrogen peroxide (H₂O₂) and 6-hydroxydopamine (6-OHDA) in PC12 cells. Pretreatment of PC12 cells with CD dose-dependently upregulated the expression of phase II antioxidant molecules governed by Nrf2. In contrast, CD failed to provide neuroprotection after silencing Nrf2 expression, indicating that this cytoprotection may be mediated by the activation of transcription factor Nrf2. Our results demonstrate that CD is a novel small molecule activator of Nrf2 in PC12 cells, and suggest that CD may be a potential candidate for the prevention of oxidative stress-mediated neurodegenerative disorders.

Monoamine Oxidase Inhibitory Activity: Methyl- versus Chlorochalcone Derivatives

Numerous studies have shown that chalcones are promising scaffolds for the development of new monoamine oxidase-B (MAO-B) inhibitors. As a continuation of our ongoing research into the development of reversible human MAO-B (hMAO-B) inhibitors, two series of twenty chalcones containing electron-donating and electron-withdrawing substituents were synthesized. All compounds were found to be competitive, selective, and reversible inhibitors of hMAO-B except (2E)-1-(4-methylphenyl)-3-(4-nitrophenyl)prop-2-en-1-one (P7) and (2E)-1-(4-chlorophenyl)-3-(4-nitrophenyl)prop-2-en-1-one (P17), which were found to be selective inhibitors of hMAO-A. The most potent hMAO-B inhibitor, (2E)-1-(4-chlorophenyl)-3-(4-ethylphenyl)prop-2-en-1-one (P16), showed a K_i value of 0.11±0.01 μm. Molecular docking simulations were carried out to identify the hypothetical binding mode for the most potent compounds in the active sites of hMAO-A and B. The ability of the compounds to cross the blood-brain barrier was assessed by parallel artificial membrane permeability assay (PAMPA). Additionally, the most potent hMAO-B inhibitor P16 showed no toxicity in cultured hepatic cells at concentrations of 5 and 25 μm.