Synthesis, Biochemistry, and Computational Studies of Brominated Thienyl Chalcones: A New Class of Reversible MAO-B Inhibitors

Redefining Chalcone Synthesis: Aldol Adduct Elimination for the Rapid Access to Thienyl Chalcones

This paper introduces a unique and novel method for synthesizing thienyl chalcones using iron oxide nanoparticles (FeONPs) as a heterogeneous catalyst. It stands out as a rare example in the literature for the synthesis of these chalcones from 1,3-diketones and various aromatic aldehydes. The magnetic FeONPs employed as the catalyst bring several advantages, including their efficiency, affordability, and ecofriendly nature, making them an attractive choice for producing thiophene chalcones. One noteworthy aspect of this methodology is the utilization of mild reaction conditions, which greatly simplify the operational aspects of the reaction. Synthesized chalcones were confirmed through the application of various techniques, proton-NMR, 13C NMR, mass spectrometry, and single-crystal X-ray diffraction analysis. These analyses provide valuable insights into the chemical compositions and structural characteristics of the synthesized compounds. Significantly, this methodology is reported for the first time in the literature, indicating its novelty and contribution to the field of chalcone synthesis.

Probing the inhibition of MAO-B by chalcones: an integrated approach combining molecular docking, ADME analysis, MD simulation, and MM-PBSA calculations

CONTEXT

Monoamine oxidase B (MAO-B), an enzyme of significant relevance in the realm of neurodegenerative disorders, has garnered considerable attention as a potential target for therapeutic intervention. Natural compounds known as chalcones have shown potential as MAO-B inhibitors. In this particular study, we employed a multimodal computational method to evaluate the inhibitory effects of chalcones on MAO-B.

METHODS

Molecular docking methods were used to study and assess the complicated binding interactions that occur between chalcones and MAO-B. This extensive analysis provided a valuable and deep understanding of possible binding methods as well as the key residues implicated in the inhibition process. Furthermore, the ADME investigation gave valuable insights into the pharmacokinetic properties of chalcones. This allowed them to be assessed in terms of drug-like attributes. The use of MD simulations has benefited in the research of ligand-protein interactions' dynamic behaviour and temporal stability. MM-PBSA calculations were also done to estimate the binding free energies and acquire a better knowledge and understanding of the binding affinity between chalcones and MAO-B. Our thorough method gives a thorough knowledge of chalcones' potential as MAO-B inhibitors, which will be useful for future experimental validation and drug development efforts in the context of neurodegenerative illnesses.

Discerning of isatin-based monoamine oxidase (MAO) inhibitors for neurodegenerative disorders by exploiting 2D, 3D-QSAR modelling and molecular dynamics simulation

Almost a billion people worldwide suffer from neurological disorders, which pose public health challenges. An important enzyme that is well-known for many neurodegenerative illnesses is monoamine oxidase (MAO). Although several promising drugs for the treatment of MAO inhibition have recently been examined, it is still necessary to identify the precise structural requirements for robust efficacy. Atom-based, field-based, and GA-MLR (genetic algorithm multiple linear regression) models were created for this investigation. All of the models have strong statistical (R2 and Q2) foundations because of both internal and external validation. Our dataset's molecule has a higher docking score than safinamide, a well-known and co-crystallized MAO-B inhibitor, as we also noticed. Using the SwissSimilarity platform, we further inquired which of our docked molecules would be the best for screening. We chose ZINC000016952895 as the screen molecule with the best binding docking score (XP score = -13.3613). Finally, the 100 ns for the ZINC000016952895-MAO-B complex in our MD investigations is stable. For compounds that we hit, also anticipate ADME properties. Our research revealed that the successful compound ZINC000016952895 might pave the way for the future development of MAO inhibitors for the treatment of neurological disease.Communicated by Ramaswamy H. Sarma.

Isatin-tethered halogen-containing acylhydrazone derivatives as monoamine oxidase inhibitor with neuroprotective effect

Sixteen isatin-based hydrazone derivatives (IS1-IS16) were synthesized and assessed for their ability to inhibit monoamine oxidases (MAOs). All the molecules showed improved inhibitory MAO-B activity compared to MAO-A. Compound IS7 most potently inhibited MAO-B with an IC50 value of 0.082 μM, followed by IS13 and IS6 (IC50 = 0.104 and 0.124 μM, respectively). Compound IS15 most potently inhibited MAO-A with an IC50 value of 1.852 μM, followed by IS3 (IC50 = 2.385 μM). Compound IS6 had the highest selectivity index (SI) value of 263.80, followed by IS7 and IS13 (233.85 and 212.57, respectively). In the kinetic study, the Ki values of IS6, IS7, and IS13 for MAO-B were 0.068 ± 0.022, 0.044 ± 0.002, and 0.061 ± 0.001 μM, respectively, and that of IS15 for MAO-A was 1.004 ± 0.171 μM, and the compounds were reversible-type inhibitors. The lead compounds were central nervous system (CNS) permeable, as per parallel artificial membrane permeability assay (PAMPA) test results. The lead compounds were examined for their cytotoxicity and potential neuroprotective benefits in hazardous lipopolysaccharide (LPS)-exposed SH-SY5Y neuroblastoma cells. Pre-treatment with lead compounds enhanced anti-oxidant levels (SOD, CAT, GSH, and GPx) and decreased ROS and pro-inflammatory cytokine (IL-6, TNF-alpha, and NF-kB) production in LPS-intoxicated SH-SY5Y cells. To confirm the promising effects of the compound, molecular docking, dynamics, and MM-GBSA binding energy were used to examine the molecular basis of the IS7-MAO-B interaction. Our findings indicate that lead compounds are potential therapeutic agents to treat neurological illnesses, such as Parkinson's disease.

Development of a New Class of Monoamine Oxidase-B Inhibitors by Fine-Tuning the Halogens on the Acylhydrazones

A total of 14 acyl hydrazine derivatives (ACH1-ACH14) were developed and examined for their ability to block monoamine oxidase (MAO). Thirteen analogues showed stronger inhibition potency against MAO-B than MAO-A. With a half-maximum inhibitory concentration of 0.14 μM, ACH10 demonstrated the strongest inhibitory activity against MAO-B, followed by ACH14, ACH13, ACH8, and ACH3 (IC50 = 0.15, 0.18, 0.20, and 0.22 μM, respectively). Structure-activity relationships suggested that the inhibition effect on MAO-B resulted from the combination of halogen substituents of the A- and/or B-rings. This series concluded that when -F was substituted to the B-ring, MAO-B inhibitory activities were high, except for ACH6. In the inhibition kinetics study, the compounds ACH10 and ACH14 were identified as competitive inhibitors, with Ki values of 0.097 ± 0.0021 and 0.10 ± 0.038 μM, respectively. In a reversibility experiment using the dialysis methods, ACH10 and ACH14 showed effective recoveries of MAO-B inhibition as much as lazabemide, a reversible reference. These experiments proposed that ACH10 and ACH14 were efficient, reversible competitive MAO-B inhibitors. In addition, the lead molecules showed good blood-brain barrier permeation with the PAMPA method. The molecular docking and molecular dynamics simulation study confirmed that the hit compound ACH10 can form a stable protein-ligand complex by forming a hydrogen bond with the NH atom in the hydrazide group of the compound.

Lead optimization study on indoline-2,3-dione derivatives as potential fatty acid amide hydrolase inhibitors

Based on the known isatin-based fatty acid amide hydrolase (FAAH) inhibitor BSS-7, we designed and synthesized two small sets (6-13 and 17-20) of N-1 and C-3 substituted isatin derivatives and evaluated them for their in vitro FAAH inhibition properties. The lead simplification by modification of bulky aryl moiety at N-1 with a flexible allyl group produced a nanomolar (IC50 = 6.7 nM, Ki = 5 nM) inhibitor 11 (Z)-3-((1H-benzo[d]imidazol-2-yl)imino)-1-allylindolin-2-one which exhibited a reversible and competitive FAAH inhibition with 1500 times more potency to BSS-7 (1.49 ± 0.03 µM). The lead compound 11 also showed a high blood-brain permeability and a significant antioxidant profile with no neurotoxicity. Docking results suggested that the inhibitor molecules occupied the active site of FAAH and offered optimal binding interactions. A molecular dynamics simulation study ascertained the stability of the lead inhibitor 11-FAAH complex. In silico ADMET profiling studies unveiled that compound 11 possesses good drug-like properties and merits further evaluation.Communicated by Ramaswamy H. Sarma.

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.

N-methylpiperazinyl and piperdinylalkyl-O-chalcone derivatives as potential polyfunctional agents against Alzheimer's disease: Design, synthesis and biological evaluation

The series of N-methylpiperazinyl and piperdinylalkyl-O-chalcone derivatives as potential polyfuctional agents against Alzheimer's disease that have been designed, synthesized and then evaluated biologically using in vitro assays for the inhibition of acetylcholinesterase (AChE) activity, AGEs, and free radical formation. The majority of synthesized compounds inhibited AChE & AGEs with additional free radical scavenging activities at nanomolar concentrations. Among these, compound 5k was found to have potent AChE inhibitory activity (IC50  = 11.6 nM), superior than the reference compound donepezil (15.68 nM) along with the good anti-AGEs and free radical formation effect. Its potency was justified by docking studies that revealed its dual binding characteristic with both catalytic active site and peripheral anionic site of AChE, simultaneously. Furthermore, the in vivo evaluation of 5k against streptozotocin (STZ)-induced dementia in rats also showed improvement of memory functions (Morris water maze test) in animals. Also, 5k inhibited STZ-inudced brain AChE activity and oxidative stress which further strengthen the observed in vitro effects. The stability of the ligand-protein complex was then analyzed using a simulation-based interaction protocol. The results revealed that these N-methylpiperazinyl and piperdinylalkyl-O-chalcone derivatives could be considered for potential polyfunctional anti-Alzheimer's molecules.

Recent Development of Novel Aminoethyl-Substituted Chalcones as Potential Drug Candidates for the Treatment of Alzheimer's Disease

No drug on the market, as a single entity, participates in different pathways involved in the pathology of Alzheimer's disease. The current study is aimed at the exploration of multifunctional chalcone derivatives which can act on multiple targets involved in Alzheimer's disease. A series of novel aminoethyl-substituted chalcones have been developed using in silico approaches (scaffold morphing, molecular docking, and ADME) and reported synthetic methods. The synthesized analogs were characterized and evaluated biologically using different in vitro assays against AChE, AGEs, and radical formation. Among all compounds, compound PS-10 was found to have potent AChE inhibitory activity (IC50 = 15.3 nM), even more than the standard drug (IC50 = 15.68 nM). Further, the in vivo evaluation of PS-10 against STZ-induced dementia in rats showed memory improvement (Morris Water Maze test) in rats. Also, PS-10 inhibited STZ-induced brain AChE activity and oxidative stress, further strengthening the observed in vitro effects. Further, the molecular dynamic simulation studies displayed the stability of the PS-10 and AChE complex. The novel aminoethyl-substituted chalcones might be considered potential multifunctional anti-Alzheimer's molecules.

Exploration of a new class of monoamine oxidase B inhibitors by assembling benzyloxy pharmacophore on halogenated chalcones

Eight derivatives of benzyloxy-derived halogenated chalcones (BB1-BB8) were synthesized and tested for their ability to inhibit monoamine oxidases (MAOs). MAO-A was less efficiently inhibited by all compounds than MAO-B. Additionally, the majority of the compounds displayed significant MAO-B inhibitory activities at 1 μM with residual activities of less than 50%. With an IC50 value of 0.062 μM, compound BB4 was the most effective in inhibiting MAO-B, followed by compound BB2 (IC50  = 0.093 μM). The lead molecules showed good activity than the reference MAO-B inhibitors (Lazabemide IC50  = 0.11 μM and Pargyline Pargyline IC50  = 0.14). The high selectivity index (SI) values for MAO-B were observed in compounds BB2 and BB4 (430.108 and 645.161, respectively). Kinetics and reversibility experiments revealed that BB2 and BB4 were reversible competitive MAO-B inhibitors with Ki values of 0.030 ± 0.014 and 0.011 ± 0.005 μM, respectively. Swiss target prediction confirmed the high probability in the targets of MAO-B for both compounds. Hypothetical binding mode revealed that the BB2 or BB4 is similarly oriented to the binding cavity of MAO-B. Based on the modelling results, BB4 showed a stable confirmation during the dynamic simulation. From these results, it was concluded that BB2 and BB4 were potent selective reversible MAO-B inhibitors and they can be considered drug candidates for treating related neurodegenerative diseases such as Parkinson's disease.

Structure-Based Design of Novel MAO-B Inhibitors: A Review

With the significant growth of patients suffering from neurodegenerative diseases (NDs), novel classes of compounds targeting monoamine oxidase type B (MAO-B) are promptly emerging as distinguished structures for the treatment of the latter. As a promising function of computer-aided drug design (CADD), structure-based virtual screening (SBVS) is being heavily applied in processes of drug discovery and development. The utilization of molecular docking, as a helping tool for SBVS, is providing essential data about the poses and the occurring interactions between ligands and target molecules. The current work presents a brief discussion of the role of MAOs in the treatment of NDs, insight into the advantages and drawbacks of docking simulations and docking software, and a look into the active sites of MAO-A and MAO-B and their main characteristics. Thereafter, we report new chemical classes of MAO-B inhibitors and the essential fragments required for stable interactions focusing mainly on papers published in the last five years. The reviewed cases are separated into several chemically distinct groups. Moreover, a modest table for rapid revision of the revised works including the structures of the reported inhibitors together with the utilized docking software and the PDB codes of the crystal targets applied in each study is provided. Our work could be beneficial for further investigations in the search for novel, effective, and selective MAO-B inhibitors.

Chalcone: A Promising Bioactive Scaffold in Medicinal Chemistry

Chalcones are a class of privileged scaffolds with high medicinal significance due to the presence of an α,β-unsaturated ketone functionality. Numerous functional modifications of chalcones have been reported, along with their pharmacological behavior. The present review aims to summarize the structures from natural sources, synthesis methods, biological characteristics against infectious and non-infectious diseases, and uses of chalcones over the past decade, and their structure–activity relationship studies are detailed in depth. This critical review provides guidelines for the future design and synthesis of various chalcones. In addition, this could be highly supportive for medicinal chemists to develop more promising candidates for various infectious and non-infectious diseases.

Synthesis and evaluation of carbamate derivatives as fatty acid amide hydrolase and monoacylglycerol lipase inhibitors

Fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) are the primary catabolic enzymes for endocannabinoids, anandamide (AEA), and 2-arachidonoyl glycerol. Numerous studies have shown that FAAH and MAGL play an important role in modulating various central nervous system activities; hence, the development of small molecule FAAH/MAGL inhibitors is an active area of research. Several small molecules possessing the carbamate scaffold are documented as potential FAAH/MAGL inhibitors. Here, we designed and synthesized a series of open chain and cyclic carbamates and evaluated their dual FAAH-MAGL inhibition properties. Phenyl [4-(piperidin-1-ylmethyl)phenyl]carbamate (2e) emerged as the most potent MAGL inhibitor (IC₅₀  = 19 nM), benzyl (1H-benzo[d]imidazol-2-yl)carbamate (3h) was the most potent FAAH inhibitor (IC₅₀  = 55 nM), and phenyl (6-fluorobenzo[d]thiazol-2-yl)carbamate (2i) egressed as a nonselective dual FAAH-MAGL inhibitor (FAAH: 82 nM, MAGL: 72 nM). The enzyme kinetics experiments revealed that the compounds inhibit FAAH/MAGL in a covalent-reversible manner, with a mixed binding mode of action. Moreover, the lead compounds were found suitable for blood-brain permeation in the parallel artificial membrane permeation assay. Furthermore, docking simulation experiments suggested that the potency of the lead compounds was governed by hydrogen bonds and hydrophobic interactions with the enzyme active sites. In silico drug-likeness and ADMETox prediction studies provided useful information on the compounds' oral absorption, metabolism, and toxicity profiles. In summary, this study afforded potent multifunctional carbamates with appreciable pharmacokinetic profiles meriting further investigation.

Synthesis and evaluation of dual fatty acid amide hydrolase-monoacylglycerol lipase inhibition and antinociceptive activities of 4-methylsulfonylaniline-derived semicarbazones

Fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) are promising targets for neuropathic pain and other CNS disorders. Based on our previous lead compound SIH 3, we designed and synthesized a series of 4-methylsulfonylphenyl semicarbazones and evaluated for FAAH and MAGL inhibition properties. Most of the compounds showed potency towards both enzymes with leading FAAH selectivity. Compound (Z)-2-(2,6-dichlorobenzylidene)-N-(4-(methylsulfonyl)phenyl)hydrazine-1-carboxamide emerged as the lead inhibitor against both FAAH (IC₅₀ = 11 nM) and MAGL (IC₅₀ = 36 nM). The lead inhibitor inhibited FAAH by non-competitive mode, but showed a mixed-type inhibition against MAGL. Molecular docking study unveiled that the docked ligands bind favorably to the active sites of FAAH and MAGL. The lead inhibitor interacted with FAAH and MAGL via π-π stacking via phenyl ring and hydrogen bonding through sulfonyl oxygen atoms or amide NH. Moreover, the stability of docked complexes was rationalized by molecular simulation studies. PAMPA assay revealed that the lead compound is suitable for blood-brain penetration. The lead compound showed better cell viability in lipopolysaccharide-induced neurotoxicity assay in SH-SY5Y cell lines. Further, in-vivo experiments unveiled that dual inhibitor was safe up to 2000 mg/kg with no hepatotoxicity. The dual FAAH-MAGL inhibitor produced significant anti-nociceptive effect in the CCI model of neuropathic pain without altering locomotion activity. Lastly, the lead compound exhibited promising ex-vivo FAAH/MAGL inhibition activity at the dose of 10 mg/kg and 20 mg/kg. Thus, these findings suggest that the semicarbazone-based lead compound can be a potential template for the development of agents for neuropathic pain.

Ameliorative effect of ethoxylated chalcone-based MAO-B inhibitor on behavioural predictors of haloperidol-induced Parkinsonism in mice: evidence of its antioxidative role against Parkinson's diseases

Parkinson's disease is a progressive neurodegenerative disorder that affects mostly elderly people above the age of 60. Previously, we have reported that the ethoxylated chalcone derivative (E)-1-(4-ethoxyphenyl)-3-(fluorophenyl)prop-2-en-1-one (E7) showed potent, reversible, and competitive MAO-B inhibition with an IC₅₀ value of 0.053 μm. The present study aims to investigate the anti-Parkinson activity of compound E7 in a haloperidol-induced animal model of mice. The disease was induced with haloperidol (1 mg/kg, intraperitoneal route) once daily for 21 days. E7 was given at dose levels of 10, 20, and 30 mg/kg/day for 21 days, consecutively. Behavioural tests were carried out during and at the end of the study. Biochemical analyses such as oxidative stress biomarkers and neurotransmitters were quantified on the brain homogenate at the end of the study. Behavioural results showed that there is a marked improvement in locomotor activity and motor coordination in the treatment group. Oxidative stress biomarkers such as SOD, CAT, and GSH levels were increased dose-dependently with a maximum at 30 mg/kg, whereas the dose-dependent decrease (30 mg/kg) in the MDA and nitrite levels were observed in the treatment groups. Levels of neurotransmitters, such as dopamine, serotonin, and noradrenaline, were increased in the treatment groups while dopamine and noradrenaline levels were more than in the standard treated group. MAO-B level was also decreased dose dependently in the treatment group in comparison with the control group. Based on the findings, it was concluded that the E7 compound exhibited anti-Parkinson activity which was more evident at 30 mg/kg oral dose as evaluated by the haloperidol-induced animal model of mice.

Halogenated Coumarin-Chalcones as Multifunctional Monoamine Oxidase-B and Butyrylcholinesterase Inhibitors

A series of halogenated coumarin-chalcones were synthesized, characterized, and their inhibitory activities against monoamine oxidases (MAOs), acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and β-site amyloid precursor protein cleaving enzyme 1 (BACE-1) were evaluated. Compound CC2 most potently inhibited MAO-B with an IC₅₀ value of 0.51 μM, followed by CC1 (IC₅₀ = 0.69 μM), with a selectivity index (SI) of >78.4 and >58.0, respectively, over MAO-A. However, none of the compounds effectively inhibited MAO-A, AChE, and BChE, except for CC2 and CC3 inhibiting BChE with IC₅₀ values of 7.00 (SI > 5.73 over AChE) and 11.8 μM, respectively. CC1 and CC2 were found to be reversible and competitive inhibitors of MAO-B, with K _i values of 0.50 ± 0.06 and 0.53 ± 0.04 μM, respectively, and CC2 was also a reversible and competitive inhibitor of BChE, with a K _i value of 2.84 ± 0.09 μM. The parallel artificial membrane permeability assay (PAMPA) method showed that lead candidates can cross the blood-brain barrier (BBB). The in vitro toxicity analysis on the Vero cell line (Normal African green monkey kidney epithelial cells) by MTT confirmed that both CC1 and CC2 were nontoxic up to 100 μg/mL, which is almost equivalent to 100 times of their effective concentration used in biological studies. In addition, CC1 and CC2 attenuated H₂O₂-induced cellular damage via their reactive oxygen species (ROS) scavenging effect. These results suggest that CC1 and CC2 are selective and competitive inhibitors of MAO-B, and that CC2 is a selective and competitive inhibitor of BChE. Molecular docking studies of lead compounds provided the possible type of interactions in the targeted enzymes. Based on the findings, both compounds, CC1 and CC2, can be considered plausible drug candidates against neurodegenerative disorders.

Discovery of Isatin-Based Carbohydrazones as Potential Dual Inhibitors of Fatty Acid Amide Hydrolase and Monoacylglycerol Lipase

Using ligand-based design strategy, a set of isatin-3-carbohydrazones was designed, synthesized and evaluated for dual fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) inhibition properties. Compound 5-chloro-N'-(5-chloro-2-oxoindolin-3-ylidene)-2-hydroxybenzohydrazide (13 b) emerged as a potent MAGL inhibitor with nanomolar activity (IC₅₀ =3.33 nM), while compound 5-chloro-N'-(1-(4-fluorobenzyl)-2-oxoindolin-3-ylidene)-2-hydroxybenzohydrazide (13 j) was the most potent selective FAAH inhibitor (IC₅₀ =37 nM). Compound 5-chloro-N'-(6-chloro-2-oxoindolin-3-ylidene)-2-hydroxybenzohydrazide (13 c) showed dual FAAH-MAGL inhibitory activity with an IC₅₀ of 31 and 29 nM respectively. Enzyme kinetics studies revealed that the isatin-based carbohydrazones are reversible inhibitors for both FAAH and MAGL. Further, blood-brain permeability assay confirmed that the lead compounds (13 b, 13 c, 13 g, 13 m and 13 q) are suitable as CNS candidates. Molecular dynamics simulation studies revealed the putative binding modes and key interactions of lead inhibitors within the enzyme active sites. The lead dual FAAH-MAGL inhibitor 13 c showed significant antioxidant activity and neuroprotection in the cell-based cytotoxicity assay. In summary, the study yielded three potent FAAH/MAGL inhibitor compounds (13 b, 13 c and 13 j) with acceptable pharmacokinetic profile and thus can be considered as promising candidates for treating neurological and mood disorders.

Privileged Pharmacophore of FDA Approved Drugs in Combination with Chalcone Framework: A New Hope for Alzheimer's Treatment

Multi-functional design of ligands emerged as a new drug design paradigm of Alzheimer's disease (AD). Given the complexity of AD, the molecules showing dual inhibition of monoamine oxidase (MAO) and acetylcholinesterase (AChE) with neuroprotective properties could prevent the progressive neural degeneration effectively. Numerous studies documented that chalcone is a privileged structural framework for the inhibition of both MAO and AChE. The recent studies suggested that the development of chalcone candidates endowed with pharmacophores of FDA approved drugs may become an active molecules in the field of current AD research. The current perspective described the recent updates of chalcone moiety linked with the pharmacophores of flurbiprofen and rivastigmine hybrids as selective ChE/MAO-B inhibitors for the prophylactic agents for AD.

A Comprehensive Review of Monoamine Oxidase-A Inhibitors in their Syntheses and Potencies

BACKGROUND

Monoamine oxidases (MAOs) play a crucial role during the development of various neurodegenerative disorders. There are two MAO isozymes, MAO-A and MAO-B. MAO-A is a flavoenzyme, which binds to the outer mitochondrial membrane and catalyzes the oxidative transformations of neurotransmitters like serotonin, norepinephrine, and dopamine.

MATERIALS AND METHODS

Focus on synthetic studies has culminated in the preparation of many MAOA inhibitors, and advancements in combinatorial and parallel synthesis have accelerated the developments of synthetic schemes. Here, we provided an overview of the synthetic protocols employed to prepare different classes of MAO-A inhibitors. We classified these inhibitors according to their molecular scaffolds and the synthetic methods used.

RESULTS

Various synthetic and natural derivatives from a different class of MAO-A inhibitors were reported.

CONCLUSION

The review provides a valuable tool for the development of a new class of various selective MAO-A inhibitors for the treatment of depression and other anxiety disorders.

Morpholine-based chalcones as dual-acting monoamine oxidase-B and acetylcholinesterase inhibitors: synthesis and biochemical investigations

Nine compounds (MO1–MO9) containing the morpholine moiety were assessed for their inhibitory activities against monoamine oxidases (MAOs) and acetylcholinesterase (AChE). Most of the compounds potently inhibited MAO-B; MO1 most potently inhibited with an IC₅₀ value of 0.030 µM, followed by MO7 (0.25 µM). MO5 most potently inhibited AChE (IC₅₀ = 6.1 µM), followed by MO9 (IC₅₀ = 12.01 µM) and MO7 most potently inhibited MAO-A (IC₅₀ = 7.1 µM). MO1 was a reversible mixed-type inhibitor of MAO-B (K_i = 0.018 µM); MO5 reversibly competitively inhibited AChE (K_i = 2.52 µM); and MO9 reversibly noncompetitively inhibited AChE (K_i = 7.04 µM). MO1, MO5 and MO9 crossed the blood–brain barrier, and were non-toxic to normal VERO cells. These results show that MO1 is a selective inhibitor of MAO-B and that MO5 is a dual-acting inhibitor of AChE and MAO-B, and that both should be considered candidates for the treatment of Alzheimer’s disease.

Trimethoxylated Halogenated Chalcones as Dual Inhibitors of MAO-B and BACE-1 for the Treatment of Neurodegenerative Disorders

Six halogenated trimethoxy chalcone derivatives (CH1-CH6) were synthesized and spectrally characterized. The compounds were further evaluated for their inhibitory potential against monoamine oxidases (MAOs) and β-secretase (BACE-1). Six compounds inhibited MAO-B more effectively than MAO-A, and the 2',3',4'-methoxy moiety in CH4-CH6 was more effective for MAO-B inhibition than the 2',4',6'-methoxy moiety in CH1-CH3. Compound CH5 most potently inhibited MAO-B, with an IC₅₀ value of 0.46 µM, followed by CH4 (IC₅₀ = 0.84 µM). In 2',3',4'-methoxy derivatives (CH4-CH6), the order of inhibition was -Br in CH5 > -Cl in CH4 > -F in CH6 at the para-position in ring B of chalcone. CH4 and CH5 were selective for MAO-B, with selectivity index (SI) values of 15.1 and 31.3, respectively, over MAO-A. CH4 and CH5 moderately inhibited BACE-1 with IC₅₀ values of 13.6 and 19.8 µM, respectively. When CH4 and CH5 were assessed for their cell viability studies on the normal African Green Monkey kidney cell line (VERO) using MTT assays, it was noted that both compounds were found to be safe, and only a slightly toxic effect was observed in concentrations above 200 µg/mL. CH4 and CH5 decreased reactive oxygen species (ROS) levels of VERO cells treated with H₂O₂, indicating both compounds retained protective effects on the cells by antioxidant activities. All compounds showed high blood brain barrier permeabilities analyzed by a parallel artificial membrane permeability assay (PAMPA). Molecular docking and ADME prediction of the lead compounds provided more insights into the rationale behind the binding and the CNS drug likeness. From non-test mutagenicity and cardiotoxicity studies, CH4 and CH5 were non-mutagenic and non-/weak-cardiotoxic. These results suggest that CH4 and CH5 could be considered candidates for the cure of neurological dysfunctions.

New Aspects of Monoamine Oxidase B Inhibitors: The Key Role of Halogens to Open the Golden Door

A large plethora of drugs and promising lead compounds contain halogens in their structures. The introduction of such moieties strongly modulates their physical-chemical features as well as pharmacokinetic and pharmacodynamic profile. The most important outcome was shown to be the ability of these halogens to favourably influence the drug-target interaction and energetic stability within the active site by the establishment of halogen bonds. This review attempted to demonstrate the key role exerted by these versatile moieties when correctly located in an organic scaffold to display Monoamine Oxidase (MAO) inhibition and selectivity towards the B isoform of this important enzyme. Human MAOs are well-recognized as therapeutic targets for mood disorders and neurodegenerative diseases and medicinal chemists were prompted to discover the structural requirements crucial to discriminate the slight differences between the active sits of the two isoforms (MAO-A and MAOB). The analysis of the structure-activity relationships of the most important scaffolds (hydrazothiazoles, coumarins, chromones, chalcones, pyrazolines) and the impact of halogen (F, Cl, Br and I) insertion on this biological activity and isozyme selectivity have been reported being a source of inspiration for the medicinal chemists.

(Hetero-)(arylidene)arylhydrazides as Multitarget-Directed Monoamine Oxidase Inhibitors

Fourteen (hetero-)(arylidene)arylhydrazide derivatives (ABH1-ABH14) were synthesized, and their inhibitory activities against monoamine oxidases (MAOs) and acetylcholinesterase (AChE) were evaluated. Compound ABH5 most potently inhibited MAO-B with an IC₅₀ value of 0.025 ± 0.0019 μM; ABH2 and ABH3 exhibited high IC₅₀ values as well. Most of the compounds weakly inhibited MAO-A, except ABH5 (IC₅₀ = 3.31 ± 0.41 μM). Among the active compounds, ABH2 showed the highest selectivity index (SI) of 174 for MAO-B, followed by ABH5 (SI = 132). ABH3 and ABH5 effectively inhibited AChE with IC₅₀ values of 15.7 ± 6.52 and 16.5 ± 7.29 μM, respectively, whereas the other compounds were weak inhibitors of AChE. ABH5 was shown to be a reversible competitive inhibitor for MAO-A and MAO-B with K_i values of 0.96 ± 0.19 and 0.024 ± 0.0077 μM, respectively, suggesting that this molecule can be considered as an interesting candidate for further development as a multitarget inhibitor relating to neurodegenerative disorders.

Selected 1,3-Benzodioxine-Containing Chalcones as Multipotent Oxidase and Acetylcholinesterase Inhibitors

Chalcones are considered effective templates for the development of monoamine oxidase (MAO) and cholinesterase (ChE) inhibitors. The present work describes the syntheses of selected 1,3-benzodioxine-containing chalcones (CD3, CD8 and CD10), and their inhibitory activities against MAO-A, MAO-B, acetylcholinesterase (AChE), and butyrylcholinesterase (BChE). Compound CD8 most potently inhibited MAO-B with an IC₅₀ value of 0.026 μM, followed by CD10 and CD3 (1.54 and 1.68 μM, respectively). CD8 potently and non-selectively inhibited MAO-A (IC₅₀ value of 0.023 μM). On the other hand, CD10 and CD8 inhibited AChE with IC₅₀ values of 5.40 and 9.57 μM, respectively. Kinetics and reversibility experiments showed that all synthesized molecules were competitive and reversible inhibitors, and the K_i values of CD8 for MAO-A and MAO-B were 0.018 and 0.0019 μM, respectively. By in vitro and in silico analyses, all compounds were found to have high passive human gastrointestinal absorptions, blood-brain barrier permeabilities, and non-toxicities. Molecular docking simulations revealed that docking affinity of each compound for MAO-B was higher than that for MAO-A. The results indicate that CD8 is a potent non-selective MAO inhibitor, and CD10 is an effective selective MAO-B inhibitor, and both possess AChE inhibitory activity. Therefore, we suggest that CD8 and CD10 be considered potential dual-targeting inhibitors of MAO and AChE for the treatment of various neurodegenerative disorders.

Ethyl Acetohydroxamate Incorporated Chalcones: Unveiling a Novel Class of Chalcones for Multitarget Monoamine Oxidase-B Inhibitors Against Alzheimer's Disease

BACKGROUND

Chalcones are considered as the selective scaffold for the inhibition of MAO-B.

OBJECTIVES

A previously synthesized ethyl acetohydroxamate-chalcones (L1-L22) were studied for their inhibitory activities against human recombinant monoamine oxidase A and B (hMAO-A and hMAO-B, respectively) and acetylcholinesterase (AChE) as multi-target directed ligands for the treatment of Alzheimer's Disease (AD).

METHODS

Enzyme inhibition studies of MAO-A, MAO-B and AChE is carried out. Computational studies such as Molecular docking, Molecular Mechanics/Generalized Born Surface Area calculations, ADMET prediction, and protein target prediction are also performed.

RESULTS

Among the screened compounds, compound L3 has most potent hMAO-B inhibition with an IC50 value of 0.028 ± 0.0016 µM, and other compounds, L1, L2, L4, L8, L12, and L21 showed significant potent hMAO-B inhibition with IC50 values of 0.051 ± 0.0014, 0.086 ± 0.0035, 0.036 ± 0.0011, 0.096 ± 0.0061, 0.083 ± 0.0016, and 0.038 ± 0.0021 µM, respectively. On the other hand, among the tested compounds, compound L13 showed highest hMAO-A inhibition with an IC50 value of 0.51± 0.051 µM and L9 has a significant value of 1.85 ± 0.045 µM. However, the compounds L3 and L4 only showed high selectivities for hMAO-B with Selectivity Index (SI) values of 621.4 and 416.7, respectively. Among the substituents in ring A of ethyl acetohydroxamate-chalcones (L1-L9), F atom at p-position (L3) showed highest inhibitory effect against hMAO-B. This result supports the uniqness and bizarre behavior of fluorine. Moreover, chalcones L3, L4, L9, L11, and L12 showed potential AChE inhibitory effect with IC50 values of 0.67, 0.85, 0.39, 0.30, and 0.45 µM, respectively. Inhibitions of hMAO-B by L3 or L4 were recovered to the level of the reversible reference (lazabemide), and were competitive with Ki values of 0.0030 ± 0.0002 and 0.0046 ± 0.0005 µM, respectively. Inhibitions of AChE by L3 and L11 were of the competitive and mixed types with Ki values of 0.30 ± 0.044 and 0.14 ± 0.0054 µM, respectively.

CONCLUSION

The studies indicated that L3 and L4 are considered to be promising multitarget drug molecules with potent, selective, and reversible competitive inhibitors of hMAO-B and with highly potent AChE inhibitory effect.

Perspective Design of Chalcones for the Management of CNS Disorders: A Mini-Review

The development of chalcone-based compounds for CNS disorders has been explored by many research groups. Chalcones are being considered as a potent organic scaffold with widespread applications in the field of drug discovery and medicinal chemistry. The planar or semi-planar geometry of chalcones with various functionalities impinged on the terminal aromatic systems renders the molecule its bio-activity including anti-cancer, anti-malarial, anti-microbial, anti-fungal, antileishmanial, anti-viral, anti-diabetic, anti-hypertensive properties, etc. Moreover, cutting-edge research has been executed in the domain of Central Nervous System (CNS) based scheme, further, their identification and classifications also remain of high interest in the field of medicinal chemistry but the specific reviews are limited. Hence, the present review highlights the significance of chalcones toward their CNS activities (up to 2019), which include anti-depressant activity, anxiolytic activity, activity with GABA receptors, acetylcholinesterase (AChE) and butyryl cholinesterase (BChE) inhibitions, activity as adenosine receptor antagonists anti-Alzheimer's agents, β-amyloid plaques imaging agents, monoamine oxidase inhibition. To our knowledge, this is the first review exclusively for CNS activity profile of chalcones.

Exploring the Therapeutic Potentials of Highly Selective Oxygenated Chalcone Based MAO-B Inhibitors in a Haloperidol-Induced Murine Model of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder of dopaminergic, noradrenergic, and serotonergic systems, in which dopamine, noradrenaline, and serotonin levels are depleted and lead to the development of motor and non-motor symptoms such as tremor, bradykinesia, weight changes, fatigue, depression, and visual hallucinations. Therapeutic strategies place much focus on dopamine replacement and the inhibition of dopamine metabolism. The present study was based on the known abilities of chalcones to act as molecular scaffolds that selectively inhibit MAO-B with the added advantage of binding reversibly. Recently, we synthesized a series of 26 chalcone compounds, amongst which (2E)-1-(2H-1,3-benzodioxol-5-yl)-3-(4-fluorophenyl)prop-2-en-1-one (O10) and (2E)-1-(2,3-dihydro-1,4-benzodioxin-6-yl)-3-(4-fluorophenyl)prop-2-en-1-one (O23) most inhibited MAO-B. Hence, the present study was performed to explore the molecular mechanisms responsible for the neuroprotective effect of O10 and O23 at varying doses such as 10, 20, and 30 mg/kg each in a haloperidol-induced murine model of PD. Both compounds were effective (though O23 was the more effective) at ameliorating extrapyramidal and non-motor symptoms in the model and improved locomotory and exploratory behaviors, reduced oxidative stress markers, and enhanced antioxidant marker and neurotransmitter levels. Furthermore, histopathological studies showed O10 and O23 both reduced neurofibrillary tangles and plaques to almost normal control levels.

Revealing the role of fluorine pharmacophore in chalcone scaffold for shifting the MAO-B selectivity: investigation of a detailed molecular dynamics and quantum chemical study

The development of highly selective monoamine oxidase-B (MAO-B) inhibitors has great therapeutic benefit in treatment of various neurodegenerative disorders. Recent study documented that shifting of fluorine atom from para to ortho position on the phenyl B ring of heteroaryl chalcones shown a remarkable shift in the selectivity and potency between MAO-A and MAO-B isoforms. Despite the large plethora of the design of new selective MAO-B inhibitors, the current paper illustrates the role and orientation of fluorine atom with remarkable MAO-B selectivity of three compounds (O23, O24 and O25), which differ from all other substituents encountered in the chalcone scaffolds is recently reported by our group. Conformational analyses of differential inhibitory effects of O23, O24 and O25 on MAO-A and MAO-B, differential analyses of complementary interactions at MAO-A/-B active sites and differential analysis of affinity binding and per-residue energy contributions are calculated by molecular dynamics study. Density functional theory based electronic structure calculations were employed with special emphasis to electrostatic potential and frontier molecular orbitals. Results of the current study can be used for lead modification and a new insight for the development of novel fluorinated chalcones for the treatment of various neurodegenerative disorders. Communicated by Ramaswamy H. Sarma.

Chalcones: Unearthing their therapeutic possibility as monoamine oxidase B inhibitors

In the last years the continuous efforts in the development of novel and effective inhibitors of human monoamine oxidases (hMAOs) promoted the discovery of new agents able to effectively and selectively bound one of the two isoforms (hMAO-A and hMAO-B). However, the parent chalcone scaffold still covers an important role in hMAOs inhibition. In the present work, we focused our attention on the researches performed in the last five years, involving chalcones or compounds that can be correlated to them. We classified the chalcones into different groups depending on their structural characteristics or common molecular properties. In this regard, we also considered chalcones based on heterocycles and compounds endowed with scaffolds containing a masked chalcone motif. When structural attributes could not be used, we took advantage of enzymatic activity to arrange compounds in a group. We followed this approach for the multitarget agents. Finally, we also analysed the naturally occurring chalcones. All the sections were discussed exhaustively and the structure-activity relationship (SAR) analyses were sustained by means of detailed images describing the effects related to the substituents or structural changes.

A New Potent and Selective Monoamine Oxidase-B Inhibitor with Extended Conjugation in a Chalcone Framework: 1-[4-(Morpholin-4-yl)phenyl]-5-phenylpenta-2,4-dien-1-one

The general blueprint for the design of monoamine oxidase-B (MAO-B) inhibitors has been based on two phenyl or heteronuclei linked via a spacer of appropriate length. In this study, 1-[4-(morpholin-4-yl)phenyl]-5-phenylpenta-2,4-dien-1-one (MO10) was prepared by the condensation of 4'-morpholinoacetophenone and cinnamaldehyde in basic alcoholic medium. MO10 was assessed for inhibitory activity against two human MAO isoforms, MAO-A and MAO-B. Interestingly, MO10 showed a remarkable inhibition against MAO-B with an IC₅₀ value of 0.044 μM along with a selectivity index of 366.13. The IC₅₀ value was better than that of lazabemide (IC₅₀ value of 0.063 μM), which was used as a reference. Kinetics studies revealed that MO10 acted as a competitive inhibitor of MAO-B, with a K_i value of 0.0080 μM. The observation of recovery of MAO-B inhibition, compared to reference levels showed MO10 to be a reversible inhibitor. MTT assays showed that MO10 was nontoxic to normal VERO cells with an IC₅₀ value of 195.44 μg/mL. SwissADME predicted that MO10 provided advantageous pharmacokinetics profiles for developing agents acting on the central nervous system, that is, high passive human gastrointestinal absorption and blood-brain barrier permeability. Molecular docking simulations showed that MO10 properly entered the aromatic cage formed by Y435, Y398, and FAD of the active site of MAO-B. On the basis of these results, MO10 can be considered a promising starting compound in development of agents for the treatment of various neurodegenerative disorders.

Novel Class of Chalcone Oxime Ethers as Potent Monoamine Oxidase-B and Acetylcholinesterase Inhibitors

Previously synthesized novel chalcone oxime ethers (COEs) were evaluated for inhibitory activities against monoamine oxidases (MAOs) and acetylcholinesterase (AChE). Twenty-two of the 24 COEs synthesized, except COE-17 and COE-24, had potent and/or significant selective inhibitory effects on MAO-B. COE-6 potently inhibited MAO-B with an IC₅₀ value of 0.018 µM, which was 105, 2.3, and 1.1 times more potent than clorgyline, lazabemide, and pargyline (reference drugs), respectively. COE-7, and COE-22 were also active against MAO-B, both had an IC₅₀ value of 0.028 µM, which was 67 and 1.5 times lower than those of clorgyline and lazabemide, respectively. Most of the COEs exhibited weak inhibitory effects on MAO-A and AChE. COE-13 most potently inhibited MAO-A (IC₅₀ = 0.88 µM) and also significantly inhibited MAO-B (IC₅₀ = 0.13 µM), and it could be considered as a potential nonselective MAO inhibitor. COE-19 and COE-22 inhibited AChE with IC₅₀ values of 5.35 and 4.39 µM, respectively. The selectivity index (SI) of COE-22 for MAO-B was higher than that of COE-6 (SI = 778.6 vs. 222.2), but the IC₅₀ value (0.028 µM) was slightly lower than that of COE-6 (0.018 µM). In reversibility experiments, inhibitions of MAO-B by COE-6 and COE-22 were recovered to the levels of reference reversible inhibitors and both competitively inhibited MAO-B, with K_i values of 0.0075 and 0.010 µM, respectively. Our results show that COE-6 and COE-22 are potent, selective MAO-B inhibitors, and COE-22 is a candidate of dual-targeting molecule for MAO-B and AChE.

Design of enamides as new selective monoamine oxidase-B inhibitors

OBJECTIVES

To develop of new class of selective and reversible MAO-B inhibitors from enamides.

METHODS

Syntheses of the titled derivatives (AD1-AD11) were achieved by reacting cinnamoyl chloride and various primary and secondary amines in basic medium. All eleven compounds were investigated for in vitro inhibitory activities against recombinant human MAO-A and MAO-B. The reversibilities of lead compound inhibitions were analysed by dialysis. MTT assays of lead compounds were performed using normal VERO cell lines.

KEY FINDINGS

Compounds AD3 and AD9 exhibited the greatest inhibitory activity against MAO-B with IC₅₀ values of 0.11 and 0.10 µm, respectively, and were followed by AD2 and AD1 (0.51 and 0.71 µm, respectively). Most of the compounds weakly inhibited MAO-A, with the exceptions AD9 and AD7, which had IC₅₀ values of 4.21 and 5.95 µm, respectively. AD3 had the highest selectivity index (SI) value for MAO-B (>363.6) and was followed by AD9 (SI 42.1). AD3 and AD9 were found to be competitive inhibitors of MAO-B with K_i values of 0.044 ± 0.0036 and 0.039 ± 0.0047 µm, respectively. Reversibility experiments showed AD3 and AD9 were reversible inhibitors of MAO-B; dialysis restored the activity of MAO-B to the reference level. MTT assays revealed AD3 and AD9 were non-toxic to normal VERO cell lines with IC₅₀ values of 153.96 and 194.04 µg/ml, respectively. Computational studies provided hypothetical binding modes for AD3 and AD9 in the binding cavities of MAO-A and MAO-B.

CONCLUSIONS

These results encourage further studies on the enamide scaffold as potential drug candidates for the treatment of Alzheimer's and Parkinson's diseases.

An Environment-friendly Synthesis of Piperonal Chalcones and Their Cytotoxic and Antioxidant Evaluation

Background:

Grindstone technique has been widely used as an efficient, consistent, more environmentally benign, solvent-free protocol for the preparation of many compounds with higher atom economy.

Methods:

A series of fourteen piperonal chalcone compounds were synthesized by this method and characterized by physical and spectral data (FT-IR, 1H NMR, Mass and elemental analysis). All chalcones were evaluated for their cytotoxic action against the cancer cell lines, MCF-7 and HepG2. One 2-pyridyl-substituted compound 14 with IC50 values 17.4±0.2 towards MCF-7 and 15.4±0.6µmol L-1 towards HepG2 cells.

Results:

The results demonstrated that the cytotoxic activity of 2-pyridyl-substituted compound shown higher activity as compared with the standard cisplatin towards HepG2 cells.

Conclusion:

Compound 14 showed good antioxidant activities in the DPPH test and H2O2 assay (IC50 = 17.23± 33/µg/mL and 20.17± 0.33µg/mL) when compared with the standard ascorbic acid (IC50=µg/mL 18.26 ± 0.22and 21.66± 1.06 µg/mL).

Chemoselective and metal-free reduction of α,β-unsaturated ketones by in situ produced benzeneselenol from O-(tert-butyl) Se-phenyl selenocarbonate

The carbon–carbon double bond of arylidene acetones and chalcones can be selectively reduced with benzeneselenol generated in situ by reacting O-(tert-butyl) Se-phenyl selenocarbonate with hydrochloric acid in ethanol. This mild, metal-free and experimentally simple reduction procedure displays considerable functional-group compatibility, products are obtained in good to excellent yields, and the use of toxic Se/CO mixture and NaSeH, or the smelly and air-sensitive benzeneselenol, is avoided.

The carbon–carbon double bond of arylidene acetones and chalcones can be selectively reduced with benzeneselenol generated in situ by reacting O-(tert-butyl) Se-phenyl selenocarbonate with hydrochloric acid in ethanol.

Excited States versus Reaction Intermediates as Active Species in Photoinduced Redox Reactions of Cyrhetrenyl and Ferrocenyl Chalcones: A 351 nm Flash Photolysis Study

The photoinduced redox reactions of two organometallic chalcones: trans, E, (η⁵-C₅H₄C(O)CH═CH-4-benzo-15-crown-5)Re(CO)₃, 1, and trans, E, (η⁵-C₅H₄C(O)CH═CH-4-benzo-15-crown-5)Fe(η⁵-C₅H₄C(O)CH═CH-4-benzo-15-crown-5), 2, were investigated in fluid solution using the flash photolysis technique. For a better understanding of the photoinduced redox processes of these organometallic chalcones, an electron donor, triethylamine (TEA), and an electron acceptor, methylviologen dichloride (MVCl₂), were chosen. Two parallel reaction paths for the decay of the intermediate 1-I, that is, the anion radical of 1, were observed in the presence of TEA. One generates a radical anion, while the other reaction path produces the Z isomer. Instead, the photoinduced reaction of 2 with TEA in MeOH generates an intense absorption band at λ_max = 660 nm, which is attributed to a 2-I·MeOH adduct. The oxidative process between 1-I and MV²⁺ in CH₃CN generates transient spectra consistent with the formation of the radical cation MV^•+. In contrast, the photoinduced reaction between 2 and MV²⁺ showed that the generation of MV^•+ occurs through a complex mechanism. MV^•+ is formed in two steps where the first one is the formation of an adduct between the long-lived metal-to-ligand charge transfer (MLCT)_{Fe→Chalcone} excited state and MV²⁺. These results have shown that intermediates 1-I and 2-I can function as photo-oxidants and photoreductants better than the chalcone short-lived excited states.

Design, synthesis and biological evaluation of oxygenated chalcones as potent and selective MAO-B inhibitors

The present study documents the synthesis of oxygenated chalcone (O1-O26) derivatives and their abilities to inhibit monoamine oxidases. All 26 derivatives examined showed potent inhibitory activity against MAO-B. Compound O23 showed the greatest inhibitory activity against MAO-B with an IC₅₀ value of 0.0021 µM, followed by compounds O10 and O17 (IC₅₀ = 0.0030 and 0.0034 µM, respectively). In addition, most of the derivatives potently inhibited MAO-A and O6 was the most potent inhibitor with an IC₅₀ value of 0.029 µM, followed by O3, O4, O9, and O2 (IC₅₀ = 0.035, 0.053, 0.072, and 0.082 µM, respectively). O23 had a high selectivity index (SI) value for MAO-B of 138.1, and O20 (IC₅₀ value for MAO-B = 0.010 µM) had an extremely high SI of >4000. In dialysis experiments, inhibitions of MAO-A and MAO-B by O6 and O23, respectively, were recovered to their respective reversible reference levels, demonstrating both are reversible inhibitors. Kinetic studies revealed that O6 and O23 competitively inhibited MAO-A and MAO-B, respectively, with respective K_i values of 0.016 ± 0.0007 and 0.00050 ± 0.00003 µM. Lead compound are also non-toxic at 200 µg/mL in normal rat spleen cells. Molecular docking simulations and subsequent Molecular Mechanics/Generalized Born Surface Area calculations provided a rationale that explained experimental data.

Emerging therapeutic potentials of dual-acting MAO and AChE inhibitors in Alzheimer's and Parkinson's diseases

No drug has been approved to prevent neuronal cell loss in patients suffering from Parkinson's disease (PD) or Alzheimer's disease (AD); despite increased comprehension of the underlying molecular causes, therapies target cognitive functional improvement and motor fluctuation control. Drug design strategies that adopt the "one protein, one target" philosophy fail to address the multifactorial aetiologies of neurodegenerative disorders such as AD and PD optimally. On the contrary, restoring neurotransmitter levels by combined combinatorial inhibition of cholinesterases, monoamine oxidases, and adenosine A_2A A receptors, in conjunction with strategies to counter oxidative stress and beta-amyloid plaque accumulation, would constitute a therapeutically robust, multitarget approach. This extensive review delineates the therapeutic advantages of combining dual-acting molecules that inhibit monoamine oxidases and cholinesterases and/or adenosine A_2A A receptors, and describes the structure-activity relationships of compound classes that include, but are not limited to, alkaloids, coumarins, chalcones, donepezil-propargylamine conjugates, homoisoflavonoids, resveratrol analogs, hydrazones, and pyrazolines. In the wake of recent advances in network biology, in silico approaches, and omics, this review emphasizes the need to consider conceptually informed research strategies for drug discovery, in the context of the mounting burden posed by chronic neurodegenerative diseases with complex aetiologies and pathophysiologies involving multiple signalling pathways and numerous drug targets.

Potent and highly selective dual-targeting monoamine oxidase-B inhibitors: Fluorinated chalcones of morpholine versus imidazole

Two series of fluorinated chalcones containing morpholine and imidazole-based compounds (f1-f8) were synthesized and evaluated for recombinant human monoamine oxidase (MAO)-A and -B as well as acetylcholinesterase inhibitory activities. Our results indicate that morpholine containing chalcones are highly selective MAO-B inhibitors having reversibility properties. All the imidazole-based fluorinated chalcones showed weak MAO inhibitions in both isoforms. Among the tested compounds, (2E)-3-(3-fluorophenyl)-1-[4-(morpholin-4-yl)phenyl]prop-2-en-1-one (f2) showed potent inhibitory activity for recombinant human MAO-B (IC₅₀  = 0.087 μM) with a high selectivity index (SI) of 517.2. In the recovery experiments using dialysis, the residual activity of MAO-B inhibited by f2 was close to that with the reversible reference inhibitor. Inhibition assays revealed that the K_i values of f1 and f2 for MAO-B were 0.027 and 0.020 μM, respectively, with competitive patterns. All the morpholine-based compounds (f1-f4) showed moderate inhibition toward acetylcholinesterase with IC₅₀ values ranging between 24 and 54 μM. All morpholine-containing compounds exhibit good blood-brain barrier permeation in the PAMPA method. The rational approach regarding the highly selective MAO-B inhibitor f2 was further ascertained by induced fit docking and molecular dynamics simulation studies.

Cholinesterase Inhibitory Activities of Selected Halogenated Thiophene Chalcones

BACKGROUND

Dual-acting human monoamine oxidase B (hMAO-B) and cholinesterase (ChE) inhibitors are more effective than the classic one-drug one-target therapy for Alzheimer's disease (AD).

METHODS

The ChE inhibitory ability of some halogenated thiophene chalcone-based molecules known to be selective hMAO-B inhibitors was evaluated.

RESULTS

Based on the IC50 values, the selected compounds were found to moderately inhibit ChE, with IC50 values in the range of 14-70 µM. Among the synthesised molecules, T8 and T6 showed the most potent inhibitory activity against AChE and BChE, respectively.

CONCLUSION

Taken together, the data revealed that T8 could be further optimized to enhance its AChE inhibitory activity.

Selected aryl thiosemicarbazones as a new class of multi-targeted monoamine oxidase inhibitors

A series of 13 phenyl substituted thiosemicarbazones (SB1-SB13) were synthesized and evaluated for their inhibitory potential towards human recombinant monoamine oxidase A and B (MAO-A and MAO-B, respectively) and acetylcholinesterase. The solid state structure of SB4 was ascertained by the single X-ray diffraction technique. Compounds SB5 and SB11 were potent for MAO-A (IC₅₀ 1.82 ± 0.14) and MAO-B (IC₅₀ 0.27 ± 0.015 μM), respectively. Furthermore, SB11 showed a high selectivity index (SI > 37.0) for MAO-B. The effects of fluorine orientation revealed that SB11 (m-fluorine) showed 28.2 times higher inhibitory activity than SB12 (o-fluorine) against MAO-B. Furthermore, inhibitions by SB5 and SB11 against MAO-A and MAO-B, respectively, were recovered to near reference levels in reversibility experiments. Both SB5 and SB11 showed competitive inhibition modes, with K _i values of 0.97 ± 0.042 and 0.12 ± 0.006 μM, respectively. These results indicate that SB5 and SB11 are selective, reversible and competitive inhibitors of MAO-A and MAO-B, respectively. Compounds SB5, SB7 and SB11 showed moderate inhibition against acetylcholinesterase with IC₅₀ values of 35.35 ± 0.47, 15.61 ± 0.057 and 26.61 ± 0.338 μM, respectively. Blood-brain barrier (BBB) permeation was studied using the parallel artificial membrane permeation assay (PAMPA) method. Molecular docking studies were carried out using AutoDock 4.2.

Imidazole bearing chalcones as a new class of monoamine oxidase inhibitors

In the present study, series of eleven (2E)-1-[4-(1H-imidazol-1-yl)substituted phenyl]-3-phenylprop-2-en-1-one (IM1-IM11) derivatives were synthesized and evaluated as inhibitors of recombinant human monoamine oxidase (MAO) A and B. The results indicate that (2E)-3-[4-(dimethylamino) phenyl]-1-[4-(1H-imidazol-1-yl) phenyl] prop-2-en-1-one (IM5) is a nonselective and reversible competitive inhibitor of MAO-A and MAO-B with IC₅₀ values of 0.30 ± 0.010 and 0.40 ± 0.017 μM, respectively ; those of (2E)-1-[4-(1H-imidazol-1-yl) phenyl]-3-(4-methylphenyl) prop-2-en-1-one (IM4) were 1.06 ± 0.090 and 0.32 ± 0.021 μM, respectively. Kinetic studies document that both IM5 and IM4 are competitive inhibitors of MAO-A and MAO-B with Ki value of 0.11 ± 0.0085 and 0.085 ± 0.0064 μM, respectively. Molecular docking studies of lead compounds further explained the binding modes in the inhibitor binding cavity of both MAO-A and MAO-B.