Novel 2,5-disubstituted-1,3,4-oxadiazole derivatives as MAO-B inhibitors: Synthesis, biological evaluation and molecular modeling studies

Parkinson's Disease: Unravelling the Medicinal Perspectives and Recent Developments of Heterocyclic Monoamine Oxidase-B Inhibitors

Parkinson's disease is a neurodegenerative condition characterized by slow movement (bradykinesia), tremors, and muscle stiffness. These symptoms occur due to the degeneration of dopamine- producing neurons in the substantia nigra region of the brain, leading to reduced dopamine levels. The development of Parkinson's Disease (PD) involves a combination of genetic and environmental factors. PD is associated with abnormal regulation of the monoamine oxidase (MAO) enzyme. Monoamine oxidase inhibitors (MAOIs) are an important class of drugs used to treat PD and other neurological disorders. In the early stages of PD, monotherapy with MAO-B inhibitors has been shown to be both safe and effective. These inhibitors are also commonly used as adjuncts in long-term disease management, as they can improve both motor and non-motor symptoms, reduce "OFF" periods, and potentially slow disease progression. However, current MAO-B inhibitors come with side effects like dizziness, nausea, vomiting, light-headedness, and fainting. Therefore, accelerating the development of new MAO-B inhibitors with fewer side effects is crucial. This review explores natural compounds that may inhibit monoamine oxidase B (MAO-B), focusing on key findings from the past seven years. It highlights the most effective heterocyclic compounds against MAO-B, including thiazolyl hydrazone, pyridoxine-resveratrol, pyridazine, isoxazole, oxadiazole, benzothiazole, benzoxazole, coumarin, caffeine, pyrazoline, piperazine, piperidine, pyrrolidine, and morpholine derivatives. The review covers in vitro, in silico, and in vivo data, along with the structure- activity relationship of these compounds. These findings offer valuable insights for the development of more effective MAO-B inhibitors and advancements in Parkinson's disease research.

Development of novel aza-stilbenes as a new class of selective MAO-B inhibitors for the treatment of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by a progressive loss of nigrostriatal dopaminergic neurons. Inhibitors of monoamine oxidase B (MAO-B) have shown promise in alleviating motor symptoms and reducing oxidative stress associated with PD. In this study, we report the novel use of an azastilbene-based compound library for screening human (h)MAO-B, followed by optimization of initial hits to obtain compounds with low nanomolar inhibitory potencies (compound 9, IC50 = 42 nM) against hMAO-B. To ensure specificity and minimize false positives due to non-specific hydrophobic interactions, we performed comprehensive selectivity profiling against hMAO-A, butyrylcholinesterase (hBChE) and acetylcholinesterase (hAChE) - enzymes with hydrophobic active sites that are structurally distinct from hMAO-B. Docking analysis with Glide provided valuable insights into the binding interactions between the inhibitors and hMAO-B and also explained the selectivity against hMAO-A. In the cell-based model of Parkinson's disease, one of the compounds significantly reduced rotenone-induced accumulation of reactive oxygen species. In addition, these compounds showed a protective effect against acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced motor dysfunction in PD model mice and reduced MPTP-induced loss of striatal tyrosine hydroxylase-positive neurons in the substantia nigra. These results make azastilbene-based compounds a promising new class of hMAO-B inhibitors with potential therapeutic applications in Parkinson's disease and related neurodegenerative disorders.

Challenging the anticolorectal cancer capacity of quinoxaline-based scaffold via triazole ligation unveiled new efficient dual VEGFR-2/MAO-B inhibitors

Monoamine oxidases (MAOs) and vascular endothelial growth factor receptor-2 (VEGFR-2) are promoters of colorectal cancer (CRC) and central signaling nodes in epithelial-mesenchymal transition (EMT) induced by activating hypoxia-inducible factors (HIFs). Herein, a novel series of rationally designed triazole-tethered quinoxalines were synthesized and evaluated against HCT-116 CRC cells. The tailored scaffolds combine the pharmacophoric themes of both VEGFR-2 inhibitors and MAO inhibitors. All the synthesized derivatives were screened utilizing the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay for their possible cytotoxic effects on normal human colonocytes, then evaluated for their anticancer activities against HCT-116 cells overexpressing MAOs. The hit derivatives 11 and 14 exhibited IC50 = 18.04 and 7.850 µM, respectively, against HCT-116cells within their EC100 doses on normal human colonocytes. Wound healing assay revealed their efficient CRC antimetastatic activities recording HCT-116 cell migration inhibition exceeding 75 %. In vitro enzymatic assays demonstrated that both 11 and 14 efficiently inhibited VEGFR-2 (IC50 = 88.79 and 9.910 nM), MAO-A (IC50 = 0.763 and 629.1 nM) and MAO-B (IC50 = 0.488 and 209.6 nM) with observed MAO-B over MAO-A selectivity (SI = 1.546 and 3.001), respectively. Enzyme kinetics studies were performed for both compounds to identify their mode of MAO-B inhibition. Furthermore, qRT-PCR analysis showed that the hits efficiently downregulated HIF-1α in HCT-116cells by 3.420 and 16.96 folds relative to untreated cells. Docking studies simulated their possible binding modes within the active sites of VEGFR-2 and MAO-B to highlight their essential structural determinants of activities. Finally, they recorded in silico drug-like absorption, distribution, metabolism, excretion, and toxicity (ADMET) profiles as well as ligand efficiency metrics.

Therapeutic potential of 1,3,4-oxadiazoles as potential lead compounds for the treatment of Alzheimer's disease

Monoamine oxidase and cholinesterase enzymes are important targets for the treatment of several neurological diseases especially depression, Parkinson disease and Alzheimer's. Here, we report the synthesis and testing of new 1,3,4-oxadiazole derivatives as novel inhibitors of monoamine oxidase enzymes (MAO-A and MAO-B) and cholinesterase enzymes (acetyl and butyryl cholinesterase (AChE, BChE). Compounds 4c, 4d, 4e, 4g, 4j, 4k, 4m, 4n displayed promising inhibitory effects on MAO-A (IC₅₀: 0.11-3.46 μM), MAO-B (IC₅₀: 0.80-3.08 μM) and AChE (IC₅₀: 0.83-2.67 μM). Interestingly, compounds 4d, 4e and 4g are multitargeting MAO-A/B and AChE inhibitors. Also, Compound 4m displayed promising MAO-A inhibition with IC₅₀ of 0.11 μM and high selectivity (∼25-fold) over MAO-B and AChE enzymes. These newly synthesized analogues represent promising hits for the development of promising lead compounds for neurological disease treatment.

Design, Synthesis, and In Vitro and In Silico Approaches of Novel Indanone Derivatives as Multifunctional Anti-Alzheimer Agents

Alzheimer's disease (AD) is a neurological, progressive illness that typically affects the elderly and is clinically distinguished by memory and cognitive decline. Due to a number of factors, including the absence of a radical treatment, an increase in the patient population over time, the high cost of care and treatment, and a significant decline in patients' quality of life, the importance of this disease has increased. These factors have all prompted increased interest among researchers in this field. The chemical structure of the donepezil molecule, the most popular and effective treatment response for AD, served as the basis for the design and synthesis of 42 novel indan-1-one derivatives in this study. Using IR, ¹H, and ¹³C NMR as well as mass spectroscopic techniques, the compounds' structures were identified. Research on the compounds' antioxidant activities, cholinesterase (ChE) enzyme inhibition, monoamine oxidase (MAO) A and B inhibitory activities, β-amyloid plaque inhibition, and cytotoxicity impact was carried out. Inhibition of β-amyloid plaque aggregation; effective inhibition of AChE, BChE, and MAO-B enzymes; and significant antioxidant activity were all demonstrated by compounds D28-D30 and D37-D39. Because of their various actions, it was hypothesized that the related compounds may be useful in treating AD symptoms as well as providing palliative care.

Research progress on the synthesis and pharmacology of 1,3,4-oxadiazole and 1,2,4-oxadiazole derivatives: a mini review

Oxadiazole is a five-membered heterocyclic compound containing two nitrogen atoms and one oxygen atom. The 1,3,4-oxadiazole and 1,2,4-oxadiazole have favourable physical, chemical, and pharmacokinetic properties, which significantly increase their pharmacological activity via hydrogen bond interactions with biomacromolecules. In recent years, oxadiazole has been demonstrated to be the biologically active unit in a number of compounds. Oxadiazole derivatives exhibit antibacterial, anti-inflammatory, anti-tuberculous, anti-fungal, anti-diabetic and anticancer activities. In this paper, we report a series of compounds containing oxadiazole rings that have been published in the last three years only (2020-2022) as there was no report or their activities described in any article in 2019, which will be useful to scientists in research fields of organic synthesis, medicinal chemistry, and pharmacology.

Synthesis of novel thiosemicarbazone derivatives and investigation of their dual AChE and MAO-B inhibitor effects

In this study, 15 thiosemicarbazone derivatives were synthesized. Analysis of the obtained compounds was performed by means of ¹ H-NMR, ¹³ C-NMR and high resolution mass spectroscopy (HRMS) spectroscopic methods. The inhibition effect of the obtained compounds on cholinesterase and monoaminoxidase (MAO) enzymes were investigated with in vitro methods. None of the compounds showed significant activity on the butyrylcholinesterase enzyme. On the other hand, compounds 3b, 3c, 3e, 3k, 3l, 3m, 3n and 3o displayed significant activity on acetylcholinesterase (AChE) while compounds 3f, 3i, 3k, 3l, 3m, 3n, 3o also showed remarkable effects on monoamine oxidase-B (MAO-B) enzymes. For the selected compounds, docking studies were performed and the enzyme active site and binding modes were determined. It was revealed that the strongest interaction with AChE and MAO-B enzyme active sites was observed with the compound 3k. Another important factor in the treatment of diseases affecting the central nervous system such as Alzheimer's is the ability of the compounds to cross the blood-brain barrier (BBB). Additionally, the agents planned for the treatment of these diseases must also pass the blood-brain barrier. Therefore, in silico BBB penetration properties of active compounds were investigated.

Synthesis of novel benzothiazole derivatives and investigation of their enzyme inhibitory effects against Alzheimer's disease

The use of dual acetylcholinesterase (AChE)-monoamine oxidase B (MAO-B) inhibitors is a new approach in the treatment of Alzheimer disease (AD). In this work, 14 new benzothiazoles (4a-4n) were designed and synthesized. In biological activity studies, the AChE, butyrylcholinesterase (BChE), MAO-A and MAO-B inhibitory potentials of all compounds were evaluated using the in vitro fluorometric method. Additionally, amyloid beta (Aβ)-aggregation inhibitory effects of active compounds were evaluated by means of an in vitro kit-based method. The biological evaluation showed that compounds 4a, 4d, 4f, 4h, 4k and 4m displayed significant activity against AChE and MAO-B enzymes. Compound 4f displayed inhibitory activity against AChE and MAO-B enzyme with IC50 values of 23.4 ± 1.1 nM and 40.3 ± 1.7 nM, respectively. It has been revealed that compound 4f may have the potential to inhibit AChE and MAO-B enzymes, as well as the ability to prevent the formation of beta amyloid plaques accumulated in the brains of patients suffering from AD. In silico studies also support the obtained biological activity findings. Compound 4f provided strong interactions with the active site of both enzymes. In particular, the interaction of compound 4f with flavin adenine dinucleotide (FAD) in the MAO-B enzyme active site is a promising and exciting finding.

Synthesis of new derivatives containing pyridine, investigation of MAO inhibitory activities and molecular docking studies

In this study, novel pyridine-containing thiazolyl hydrazone derivatives were synthesized. Structure determinations of the compounds were performed using ¹H NMR, ¹³C NMR and HRMS techniques. The biological activities of the compounds were evaluated against MAO enzymes by in vitro fluorometric method. As a result of activity studies, compound 3a showed selective inhibitory activity against MAO-B enzyme with IC₅₀ = 0.088 + 0.003 µM. The selectivity index of this compound is greater than 1136. Molecular docking studies were carried out using 2V5Z crystal. It has been observed that docking studies and activity studies are in harmony.

Novel imidazole derivatives as potential aromatase and monoamine oxidase-B inhibitors against breast cancer

The activity of the synthesized compounds against breast cancer was investigated. Molecular docking studies were performed against aromatase, MAO-B, and Caspase-3 enzymes.

Neuroprotective evaluation of novel substituted 1,3,4-oxadiazole and aroylhydrazone derivatives

The paper reports on the facile and convenient synthesis of a series of novel 2,5-substituted 1,3,4-oxadiazoles 3a-f and that of aroylhydrazone-based molecular hybrids 5a-g from readily available starting materials. The structure of the compounds was confirmed by IR, ¹H-NMR, ¹³C-NMR and HRESI-MS spectral data. The toxicological potential of the compounds was evaluated by monitoring the synaptosomal viability and the levels of reduced glutathione in rat brain synaptosomes, isolated by Percoll gradient. The neuroprotective effects were assessed in vitro in a model of 6-hydroxydopamine-induced neurotoxicity. Administered alone, at a concentration of 40 µM, most of the 1,3,4-oxadiazole derivatives and all of the hydrazone derivatives exhibited weak statistically significant neurotoxic effects, compared to the control. Two of the compounds from the novel oxadiazoles 3a and 3d did not have any toxicity. In a model of 6-OHDA-induced oxidative stress, again 3a and 3d and all aroylhydrazone derivatives 5a-g revealed statistically significant neuroprotective effect by preserving the synaptosomal viability and the level of reduced glutathione, against the toxic agent. Some of the compounds may have neuroprotective effects due to possible stabilization of the synaptosomal membrane and/or because of the preserved reduced glutathione. Additionally, all the compounds display a good predicted ADME profile.

Design, synthesis, biological activity, molecular docking, and molecular dynamics of novel benzimidazole derivatives as potential AChE/MAO-B dual inhibitors

To develop new acetylcholinesterase (AChE)-monoamine oxidase-B (MAO-B) dual inhibitors against Alzheimer's disease, the benzimidazole ring, which has a propargyl side chain with previously proven selective MAO-B inhibitory activity, was used as the main structure. Moreover, like donepezil, it was thought that the enzyme AChE would provide π-π interactions with the peripheral anionic side in this structure. Piperazine derivatives were chosen for the cationic active site. The synthesis of the compounds was carried out in five steps. The structures of the compounds were determined using ¹ H-NMR (nuclear magnetic resonance), ¹³ C-NMR, and high-resolution mass spectrometry spectroscopic methods. First, the in vitro AChE, butyrylcholinesterase (BChE), MAO-A, and MAO-B inhibitory potentials of the obtained compounds were investigated. As a result of activity tests, compounds 5b, 5e, 5g, and 5h showed inhibitory activity against AChE; compounds 5e and 5g showed inhibitory activity against MAO-B. None of the compounds showed inhibitory activity against BChE or MAO-A. Compounds 5e and 5g showed dual inhibition. Among these compounds, compound 5g had inhibition potential similar to that of donepezil and selegiline. For compound 5g, further kinetic studies and Aβ-plaque inhibitory potentials were investigated using in vitro methods. Molecular docking studies were performed using both AChE and hMAO-B crystals to elucidate the compound's interactions with the enzyme active site. The binding modes of the compound on AChE were fully elucidated by molecular dynamics studies.

Novel Thiosemicarbazone Derivatives: In Vitro and In Silico Evaluation as Potential MAO-B Inhibitors

MAO-B inhibitors are frequently used in the treatment of neurodegenerative diseases such as Parkinson’s and Alzheimer’s. Due to the limited number of compounds available in this field, there is a need to develop new compounds. In the recent works, it was shown that various thiosemicarbazone derivatives show hMAO inhibitory activity in the range of micromolar concentration. It is thought that benzofuran and benzothiophene structures may mimic structures such as indane and indanone, which are frequently found in the structures of such inhibitors. Based on this view, new benzofuran/benzothiophene and thiosemicarbazone hybrid compounds were synthesized, characterized and screened for their hMAO-A and hMAO-B inhibitory activity by an in vitro fluorometric method. The compounds including methoxyethyl substituent (2b and 2h) were found to be the most effective agents in the series against MAO-B enzyme with the IC₅₀ value of 0.042 ± 0.002 µM and 0.056 ± 0.002 µM, respectively. The mechanism of hMAO-B inhibition of compounds 2b and 2h was investigated by Lineweaver–Burk graphics. Compounds 2b and 2h were reversible and non-competitive inhibitors with similar inhibition features as the substrates. The K_i values of compounds 2b and 2h were calculated as 0.035 µM and 0.046 µM, respectively, with the help of secondary plots. The docking study of compound 2b and 2h revealed that there is a strong interaction between the active sites of hMAO-B and analyzed compound.

Novel thiazolyl-hydrazone derivatives including piperazine ring: synthesis, in vitro evaluation, and molecular docking as selective MAO-A inhibitor

MAO-A inhibitors are used in the treatment of depression. There are many studies showing that the thiazolyl-hydrazone structure is a pharmacophore structure for the MAO enzyme. In previous studies by our team, activity studies were carried out with thiazolyl-hydrazone derivatives containing pyrrolidine, morpholine, and piperazine. All of them were displayed MAO-A selective inhibition profile. Additionally, derivatives containing piperazine ring were most active. For this purpose, thiazolyl-hydrazone derivatives containing piperazine were synthesized, but this time an active group, formyl group, was added to the piperazine ring as a substituent. Based on this view, new thiazolyl-hydrazone compounds were synthesized, characterized, and screened for their hMAO-A and hMAO-B inhibitory activity by an in vitro fluorometric method. The structure of the compound was tried to be fully elucidated using 2D NMR technique. The compound including 2,4-dimethyl substituent (3i) were found to be the most effective agents in the series against MAO-A enzyme with the IC₅₀ value of 0.080 ± 0.003 µM. The docking study of compound 3i revealed that there is a strong interaction between the active sites of hMAO-A and analyzed compound.