Inhibition of monoamine oxidase by phthalide analogues

Potent, selective and reversible hMAO-B inhibition by benzalphthalides: Synthesis, enzymatic and cellular evaluations and virtual docking and predictive studies

Monoaminooxidases (MAOs) are important targets for drugs used in the treatment of neurological and psychiatric disorders and particularly on Parkinson's Disease (PD). Compounds containing a trans-stilbenoid skeleton have demonstrated good selective and reversible MAO-B inhibition. Here, twenty-two (Z)-3-benzylidenephthalides (benzalphthalides, BPHs) displaying a trans-stilbenoid skeleton have been synthesised and evaluated as inhibitors of the MAO-A and MAO-B isoforms. Some BPHs have selectively inhibited MAO-B, with IC50 values ranging from sub-nM to μM. The most potent compound with IC50 = 0.6 nM was the 3',4'-dichloro-BPH 16, which showed highly selective and reversible MAO-B inhibitory activity. Furthermore, the most selective BPHs displayed a significant protection against the apoptosis, and mitochondrial toxic effects induced by 6-hydroxydopamine (6OHDA) on SH-SY5Y cells, used as a cellular model of PD. The results of virtual binding studies on the most potent compounds docked in MAO-B and MAO-A were in agreement with the potencies and selectivity indexes found experimentally. Additionally, related to toxicity risks, drug-likeness and ADME properties, the predictions found for the most relevant BPHs in this research were within those ranges established for drug candidates.

Monoamine oxidase B inhibitors based on natural privileged scaffolds: A review of systematically structural modification

Monoamine oxidase is a flavin enzyme that catalyzes the oxidation of monoamine neurotransmitters in the brain. Various toxic by-products, aldehydes and hydrogen peroxide produced during the catalytic process, can cause oxidative stress and neuronal cell death. Overexpression of MAO-B and insufficient dopamine concentration are recognized as pathological factors in neurodegenerative diseases (NDs) including Parkinson's disease (PD) and Alzheimer's disease (AD). Therefore, the inhibition of MAO-B is an attractive target for the treatment of NDs. Despite significant efforts, few selective and reversible MAO-B inhibitors have been clinically approved. Natural products have emerged as valuable sources of lead compounds in drug discovery. Compounds such as chromone, coumarin, chalcone, caffeine, and aurone, present in natural structures, are considered as privileged scaffolds in the synthesis of MAO-B inhibitors. In this review, we summarized the structure-activity relationship (SAR) of MAO-B inhibitors based on the naturally privileged scaffolds over the past 20 years. Additionally, we proposed a balanced discussion on the advantages and limitations of natural scaffold-based MAO-B inhibitors with providing a future perspective in drug development.

Microbial Metabolites of 3-n-butylphthalide as Monoamine Oxidase A Inhibitors

Novel compounds with antidepressant activity via monoamine oxidase inhibition are being sought. Among these, derivatives of 3-n-butylphthalide, a neuroprotective lactone from Apiaceae plants, may be prominent candidates. This study aimed to obtain the oxidation products of 3-n-butylphthalide and screen them regarding their activity against the monoamine oxidase A (MAO-A) isoform. Such activity of these compounds has not been previously tested. To obtain the metabolites, we used fungi as biocatalysts because of their high oxidative capacity. Overall, 37 strains were used, among which Penicillium and Botrytis spp. were the most efficient, leading to the obtaining of three main products: 3-n-butyl-10-hydroxyphthalide, 3-n-butylphthalide-11-oic acid, and 3-n-butyl-11-hydroxyphthalide, with a total yield of 0.38-0.82 g per g of the substrate, depending on the biocatalyst used. The precursor-3-n-butylphthalide and abovementioned metabolites inhibited the MAO-A enzyme; the most active was the carboxylic acid derivative of the lactone with inhibitory constant (K_i) < 0.001 µmol/L. The in silico prediction of the drug-likeness of the metabolites matches the assumptions of Lipinski, Ghose, Veber, Egan, and Muegge. All the compounds are within the optimal range for the lipophilicity value, which is connected to adequate permeability and solubility.

Introduction of benzyloxy pharmacophore into aryl/heteroaryl chalcone motifs as a new class of monoamine oxidase B inhibitors

The inhibitory action of fifteen benzyloxy ortho/para-substituted chalcones (B1-B15) was evaluated against human monoamine oxidases (hMAOs). All the molecules inhibited hMAO-B isoform more potently than hMAO-A. Furthermore, the majority of the molecules showed strong inhibitory actions against hMAO-B at 10 μM level with residual activities of less than 50%. Compound B10 has an IC₅₀ value of 0.067 μM, making it the most potent inhibitor of hMAO-B, trailed by compound B15 (IC₅₀ = 0.12 μM). The thiophene substituent (B10) in the A-ring exhibited the strongest hMAO-B inhibition structurally, however, increased residue synthesis did not result in a rise in hMAO-B inhibition. In contrast, the benzyl group at the para position of the B-ring displayed more hMAO-B inhibition than the other positions. Compounds B10 and B15 had relatively high selectivity index (SI) values for hMAO-B (504.791 and 287.600, respectively). K_i values of B10 and B15 were 0.030 ± 0.001 and 0.033 ± 0.001 μM, respectively. The reversibility study showed that B10 and B15 were reversible inhibitors of hMAO-B. PAMPA assay manifested that the benzyloxy chalcones (B10 and B15) had a significant permeability and CNS bioavailability with Pe value higher than 4.0 × 10^-6 cm/s. Both compounds were stabilized in protein-ligand complexes by the π-π stacking, which enabled them to bind to the hMAO-B enzyme's active site incredibly effectively. The hMAO-B was stabilized by B10- and B15-hMAO-B complexes, with binding energies of - 74.57 and - 87.72 kcal/mol, respectively. Using a genetic algorithm and multiple linear regression, the QSAR model was created. Based on the best 2D and 3D descriptor-based QSAR model, the following statistics were displayed: R² = 0.9125, Q²_loo = 0.8347. These findings imply that B10 and B15 are effective, selective, and reversible hMAO-B inhibitors.

Discovery of 3, 6-disubstituted isobenzofuran-1(3H)-ones as novel inhibitors of monoamine oxidases

Monoamine oxidases A and B (MAO-A and MAO-B) play important roles in biogenic amine metabolism, oxidative stress, and chronic inflammation. Particularly, MAO-B selective inhibitors are promising therapeutic choices for the treatment of neurodegenerative diseases, such as Pakinson's disease and Alzheimer's disease. Herein, novel 3,6-disubstituted isobenzofuran-1(3H)-ones were designed, synthesized and evaluated in vitro as inhibitors of monoamine oxidases A and B. Structure-activity relationships were investigated, and all of the compounds with (R)-3-hydroxy pyrrolidine moiety on the 6-position displayed preferable inhibition toward the MAO-B isoform. Among them, compounds 6c with a 4'-fluorobenzyl ring and 6m bearing a 3',4'-difluorobenzyl ring on the 3-position were the most potent MAO-B inhibitors with IC₅₀ values of 0.35 μM and 0.32 μM, respectively. The binding mode of compound 6m in MAO-B was predicted by CDOCKER program, revealing that (R)-3-hydroxypyrrolidine moiety is a critical structural feature for this series of MAO-B inhibitors. Compound 6m could serve as a new template structure for developing potent and selective MAO-B inhibitors.

Exploration of the Detailed Structure-Activity Relationships of Isatin and Their Isomers As Monoamine Oxidase Inhibitors

Monoamine oxidase (MAO) is a protein with a key function in the catabolism of neuroamines in both central and peripheral parts of the body. MAO-A and -B are two isozymes of this enzyme which have emerged to be considered as a drug target for the treatment of neurodenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD). Isatin is an endogenous small fragment, reversible inhibitor for MAO enzymes and is more selective for MAO-B than -A. Isatin is responsible for increasing the dopamine level in the brain by the inhibition of an MAO enzyme. The very few selective and reversible inhibitors existing for MAO proteins and the intensity of neurological diseases in humanity have opened a new door for researchers. Isatin has a polypharmacological profile in medicinal chemistry, is a reversible inhibitor for both the MAOs, and shows high selectivity potent inhibition for MAO-B. In this review, we discuss isatins and their analogues phthalide and phthalimide with structure-activity relationships (SARs), and this comprehensive information accelerates the ideas for design and development of a new class of MAO inhibitors for neurodegenerative diseases.

Revealing the role of the benzyloxy pharmacophore in the design of a new class of monoamine oxidase-B inhibitors

The conceptual layout of monoamine oxidase (MAO) inhibitors has been modified to explore their potential biological application in the case of neurological disorders for the time being. The current review article is an effort to display the summation of innovative conceptual prospects of MAO inhibitors and their intriguing chemistry and bioactivity. Based on this scenario, we emphasize the pivotal role of the benzyloxy moiety attached to scaffolds like oxadiazolones, indolalkylamines, safinamide, caffeine, benzofurans, α-tetralones, β-nitrostyrene, benzoquinones, coumarins, indoles, chromones, and chromanone analogs, while acting as an MAO inhibitor.

Design and synthesis of novel 3,4-dihydrocoumarins as potent and selective monoamine oxidase-B inhibitors with the neuroprotection against Parkinson's disease

The monoamine oxidase-B (MAO-B) inhibitors with neuroprotective effects are better for Parkinson's disease (PD) treatment, due to the complicated pathogenesis of PD. To develop new hMAO-B inhibitors with neuroprotection, a novel series of 3,4-dihydrocoumarins was designed as selective and reversible hMAO-B inhibitors to treat PD. Most compounds showed potent and selective inhibition for hMAO-B over hMAO-A with IC₅₀ values ranging from nanomolar to sub-nanomolar. Among them, compound 4d was the most potent hMAO-B inhibitor (IC₅₀ = 0.37 nM) being about 20783-fold more active than iproniazid, and exhibited the highest selectivity for hMAO-B (SI > 270,270). Kinetic studies revealed that compound 4d was a reversible and competitive inhibitor of hMAO-B. Neuroprotective studies indicated that compound 4d could protect PC12 cells from the damage induced by 6-OHDA and rotenone. Besides, compound 4d did not exhibit acute toxicity at a dose up to 2500 mg/kg (po), and could cross the BBB in parallel artificial membrane permeability assay. More importantly, compound 4d was able to significantly prevent the motor deficits in the MPTP-induced PD model. These results indicate that compound 4d is an effective and promising candidate against PD.

Discovery of monoamine oxidase inhibitors by medicinal chemistry approaches

Neuropsychiatric disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD) and depression, have seriously inconvenienced the lives of patients. Growing evidence indicates that these diseases are closely related to the monoamine oxidase (MAO) enzyme, making it an attractive target for the exploitation of potent MAO inhibitors (MAOIs) with high selectivity and low side effects. Although various MAOIs have been discovered, the discovery of an ideal MAOI is not an easy task. In this review, we discuss the currently available rational design strategies for obtaining ideal MAOIs, including ligand-based and receptor-based design strategies, and these strategies were further illustrated with the aid of specific examples from the recent literature. To better understanding the biological activity of MAO, we also highlight the binding modes of typical inhibitors against MAO. Besides, advanced strategies for finding upcoming potent MAOIs were prospected.

Propargylamine as functional moiety in the design of multifunctional drugs for neurodegenerative disorders: MAO inhibition and beyond

Much progress has been made in designing analogues that can potentially confer neuroprotection against debilitating neurodegenerative disorders, yet the multifactorial pathogenesis of this cluster of diseases remains a stumbling block for the successful design of an 'ultimate' drug. However, with the growing popularity of the "one drug, multiple targets" paradigm, many researchers have successfully synthesized and evaluated drug-like molecules incorporating a propargylamine function that shows potential to serve as multifunctional drugs or multitarget-directed ligands. It is the aim of this review to highlight the reported activities of these propargylamine derivatives and their prospect to serve as drug candidates for the treatment of neurodegenerative disorders.

Recent developments on the structure–activity relationship studies of MAO inhibitors and their role in different neurological disorders

Development of MAO inhibitors as effective drug candidates for the management and/or treatment of different neurological disorders.

New Frontiers in Selective Human MAO-B Inhibitors

Accumulating evidence shows a relationship between the human MAO-B (hMAO-B) enzyme and neuropsychiatric/degenerative disorder, personality traits, type II alcoholism, borderline personality disorders, aggressiveness and violence in crime, obsessive-compulsive disorder, depression, suicide, schizophrenia, anorexia nervosa, migraine, dementia, and PD. Thus, MAO-B represents an attractive target for the treatment of a number of human diseases. The discovery, development, and therapeutic use of drugs that inhibit MAO-B are major challenges for future therapy. Various compounds and drugs that selectively target this isoform have been discovered recently. These agents are synthetic compounds or natural products and their analogues, including chalcones, pyrazoles, chromones, coumarins, xanthines, isatin derivatives, thiazolidindiones, (thiazol-2-yl)hydrazones, and analogues of marketed drugs. Despite considerable efforts in understanding the binding interaction with specific substrates or inhibitors, structural information available for the rational design of new hMAO-B inhibitors remains unsatisfactory. Therefore, the quest for novel, potent, and selective hMAO-B inhibitors remains of high interest.

Bioactive benzofuran derivatives: An insight on lead developments, radioligands and advances of the last decade

Benzofuran core is a highly versatile, presents in many important natural products and natural drugs. Many benzofuran containing synthetic drugs and clinical candidates have been derived from natural products. The present review will provide an insight on lead design-developments of the decade, clinical candidates and PET tracer radio-ligands containing benzofuran core along with brief target biology. Brief of the all approved drugs containing benzofuran core also have been enclosed. Main therapeutic areas covered are Cancer, Neurological disorders including anti-psychotic agent and diabetes.

Acetophenone derivatives: novel and potent small molecule inhibitors of monoamine oxidase B

Compounds 1j and 2e were both potent and selective MAO-B inhibitors.