Deep eutectic solvent mediated synthesis of 3,4-dihydropyrimidin-2(1H)-ones and evaluation of biological activities targeting neurodegenerative disorders

Substitution of hazardous and often harmful organic solvents with "green" and "sustainable" alternative reaction media is always desirous. Ionic liquids (IL) have emerged as valuable and versatile liquids that can replace most organic solvents in a variety of syntheses. However, recently new types of low melting mixtures termed as Deep Eutectic Solvents (DES) have been utilized in organic syntheses. DES are non-volatile in nature, have sufficient thermal stability, and also have the ability to be recycled and reused. Hence DES have been used as alternative reaction media to perform different organic reactions. The availability of green, inexpensive and easy to handle alternative solvents for organic synthesis is still scarce, hence our interest in DES mediated syntheses. Herein we have investigated Biginelli reaction in different DES for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones. Monoamine oxidases and cholinesterases are important drug targets for the treatment of various neurological disorders such as Alzheimer's disease, Parkinson's disease, depression and anxiety. The compounds synthesized herein were evaluated for their inhibitory potential against these enzymes. Some of the compounds were found to be highly potent and selective inhibitors. Compounds 1 h and 1c were the most active monoamine oxidase A (MAO A) (IC₅₀ = 0.31 ± 0.11 µM) and monoamine oxidase B (MAO B) (IC₅₀ = 0.34 ± 0.04 µM) inhibitors respectively. All compounds were selective AChE inhibitors and did not inhibit BChE (<29% inhibition). Compound 1 k (IC₅₀ = 0.13 ± 0.09 µM) was the most active AChE inhibitor.

Biphenylpiperazine Based MAO Inhibitors: Synthesis, Biological Evaluation, Reversibility and Molecular Modeling Studies

In this study, 21 new 1,4-biphenylpiperazine derivatives were designed, synthesized and evaluated as monoamine oxidase (MAO) inhibitors by in vitro fluorometric method. All these compounds exhibited inhibitory activity against hMAO enzymes, 17 analogues of them showed selectivity towards hMAO-B over hMAO-A enzyme. Compound 20 exhibited the best activity and selectivity towards hMAO-B with IC₅₀ value of 53 nM and selectivity index of 1122 folds over MAO-A, compared to the reference drugs rasagiline (IC₅₀ = 66 nM) and selegiline (IC₅₀ = 40 nM). Kinetic study and reversibility test of the most potent compound (20) revealed that it is reversible and mixed competitive inhibitor (K_i value is 17 nM for the inhibition of hMAO-B). Compound 20 was evaluated against normal NIH/3T3 mouse embryonic fibroblast cell lines and it was found that it is non-cytotoxic at its effective concentration against hMAO-B. Moreover, compound 20 and the most potent compounds have acceptable ADME properties and good pharmacokinetics profiles. Molecular docking simulations were performed for explanation and elucidation for the biological activity of compounds 19 and 20. Accordingly, 1,4- biphenylpiperazine derivatives can be considered as a promising lead to produce more potent and safer MAO inhibitors for management of various neurological disorders.

Curcumin-Coumarin Hybrid Analogues as Multitarget Agents in Neurodegenerative Disorders

Neurodegenerative diseases have a complex nature which highlights the need for multitarget ligands to address the complementary pathways involved in these diseases. Over the last decade, many innovative curcumin-based compounds have been designed and synthesized, searching for new derivatives having anti-amyloidogenic, inhibitory of tau formation, as well as anti-neuroinflammation, antioxidative, and AChE inhibitory activities. Regarding our experience studying 3-substituted coumarins with interesting properties for neurodegenerative diseases, our aim was to synthesize a new series of curcumin–coumarin hybrid analogues and evaluate their activity. Most of the 3-(7-phenyl-3,5-dioxohepta-1,6-dien-1-yl)coumarin derivatives 11–18 resulted in moderated inhibitors of hMAO isoforms and AChE and BuChE activity. Some of them are also capable of scavenger the free radical DPPH. Furthermore, compounds 14 and 16 showed neuroprotective activity against H₂O₂ in SH-SY5Y cell line. Nanoparticles formulation of these derivatives improved this property increasing the neuroprotective activity to the nanomolar range. Results suggest that by modulating the substitution pattern on both coumarin moiety and phenyl ring, ChE and MAO-targeted derivatives or derivatives with activity in cell-based phenotypic assays can be obtained.

Design, synthesis and evaluation of cinnamic acid hybrids as multi-target-directed agents for the treatment of Alzheimer's disease

Herein, combining 1,2,3,4-tetrahydroisoquinoline and benzylpiperidine groups into cinnamic acid derivatives, a series of novel cinnamic acid hybrids was rationally designed, synthesized and evaluated by the multi-target-directed ligands (MTDLs) strategy. Hybrid 4e was the most promising one among these hybrids with a reversible huBuChE inhibitor (IC₅₀ = 2.5 μM) and good MAO-B inhibition activity (IC₅₀ = 1.3 μM) and antioxidant potency (ORAC = 0.4 eq). Moreover, compound 4e significantly inhibited self-mediated Aβ_1-42 aggregation (65.2% inhibition rate). Compound 4e exhibited remarkable anti-inflammatory propery and neuroprotective effect. Furthermore, compound 4e displayed favourable blood-brain barrier penetration via parallel artificial membrane permeation assay (PAMPA). The obtained results also revealed that compound 4e significantly improved dyskinesia recovery rate and response efficiency on AD model zebrafish. Further, 4e did not show obvious acute toxicity at dose up to 1500 mg/kg in vivo and improved scopolamine-induced memory impairment. Importantly, compound 4e showed good stability in both artificial gastric fluid and artificial intestinal fluid. Therefore, compound 4e presented a promising multi-targeted active molecule for treating AD.

4-Oxoquinolines and monoamine oxidase: When tautomerism matters

4-Oxoquinoline derivatives have been often used in drug discovery programs due to their pharmacological properties. Inspired on chromone and 4-oxoquinoline chemical structure similarity, a small series of quinoline-based compounds was obtained and screened, for the first time, toward human monoamine oxidases isoforms. The data showed the N-(3,4-dichlorophenyl)-1-methyl-4-oxo-1,4-dihydroquinoline-3-carboxamide 10 was the most potent and selective MAO-B inhibitor (IC₅₀ = 5.30 ± 0.74 nM and SI: ≥1887). The data analysis showed that prototropic tautomerism markedly influences the biological activity. The unequivocal characterisation of the quinoline tautomers was performed to understand the attained data. To our knowledge, there have been no prior reports on the characterisation of quinolone tautomers by 2D NMR techniques, namely by ¹H-¹⁵N HSQC and ¹H-¹⁵N HMBC, which are proposed as expedite tools for medicinal chemistry campaigns. Computational studies on enzyme-ligand complexes, obtained after MM-GBSA calculations and molecular dynamics simulations, supported the experimental data.

Synthesis and in vitro study of nitro- and methoxy-2-phenylbenzofurans as human monoamine oxidase inhibitors

A new series of 2-phenylbenzofuran derivatives were designed and synthesized to determine relevant structural features for the MAO inhibitory activity and selectivity. Methoxy substituents were introduced in the 2-phenyl ring, whereas the benzofuran moiety was not substituted or substituted at the positions 5 or 7 with a nitro group. Substitution patterns on both the phenyl ring and the benzofuran moiety determine the affinity for MAO-A or MAO-B. The 2-(3-methoxyphenyl)-5-nitrobenzofuran 9 was the most potent MAO-B inhibitor (IC₅₀ = 0.024 µM) identified in this series, whereas 7-nitro-2-phenylbenzofuran 7 was the most potent MAO-A inhibitor (IC₅₀ = 0.168 µM), both acting as reversible inhibitors. The number and position of the methoxyl groups on the 2-phenyl ring, have an important influence on the inhibitory activity. Molecular docking studies confirmed the experimental results and highlighted the importance of key residues in enzyme inhibition.

How to Separate Kinase Inhibition from Undesired Monoamine Oxidase A Inhibition-The Development of the DYRK1A Inhibitor AnnH75 from the Alkaloid Harmine

The β-carboline alkaloid harmine is a potent DYRK1A inhibitor, but suffers from undesired potent inhibition of MAO-A, which strongly limits its application. We synthesized more than 60 analogues of harmine, either by direct modification of the alkaloid or by de novo synthesis of β-carboline and related scaffolds aimed at learning about structure-activity relationships for inhibition of both DYRK1A and MAO-A, with the ultimate goal of separating desired DYRK1A inhibition from undesired MAO-A inhibition. Based on evidence from published crystal structures of harmine bound to each of these enzymes, we performed systematic structure modifications of harmine yielding DYRK1A-selective inhibitors characterized by small polar substituents at N-9 (which preserve DYRK1A inhibition and eliminate MAO-A inhibition) and beneficial residues at C-1 (methyl or chlorine). The top compound AnnH75 remains a potent DYRK1A inhibitor, and it is devoid of MAO-A inhibition. Its binding mode to DYRK1A was elucidated by crystal structure analysis, and docking experiments provided additional insights for this attractive series of DYRK1A and MAO-A inhibitors.

Design, Synthesis, and Biological Evaluation of Pyridazinones Containing the (2-Fluorophenyl) Piperazine Moiety as Selective MAO-B Inhibitors

Twelve pyridazinones (T1–T12) containing the (2-fluorophenyl) piperazine moiety were designed, synthesized, and evaluated for monoamine oxidase (MAO) -A and -B inhibitory activities. T6 was found to be the most potent MAO-B inhibitor with an IC₅₀ value of 0.013 µM, followed by T3 (IC₅₀ = 0.039 µM). Inhibitory potency for MAO-B was more enhanced by meta bromo substitution (T6) than by para bromo substitution (T7). For para substitution, inhibitory potencies for MAO-B were as follows: -Cl (T3) > -N(CH₃)₂ (T12) > -OCH₃ (T9) > Br (T7) > F (T5) > -CH₃ (T11) > -H (T1). T6 and T3 efficiently inhibited MAO-A with IC₅₀ values of 1.57 and 4.19 µM and had the highest selectivity indices (SIs) for MAO-B (120.8 and 107.4, respectively). T3 and T6 were found to be reversible and competitive inhibitors of MAO-B with K_i values of 0.014 and 0.0071, respectively. Moreover, T6 was less toxic to healthy fibroblast cells (L929) than T3. Molecular docking simulations with MAO binding sites returned higher docking scores for T6 and T3 with MAO-B than with MAO-A. These results suggest that T3 and T6 are selective, reversible, and competitive inhibitors of MAO-B and should be considered lead candidates for the treatment of neurodegenerative disorders like Alzheimer’s disease.

Highly efficient synthesis and monoamine oxidase B inhibitory profile of demethyleneberberine, columbamine and palmatine

The biosynthesis of berberine alkaloids is thought to begin with the demethylation of berberine followed by methylation reactions to generate other type berberine alkaloids. This seemingly expeditious way to access berberine alkaloids has been stagnated for over half a century due to certain vexing synthetic problems, such as low isolated yield, complex operations and toxic reagents. We further investigated this bioinspired semi-synthesis strategy and significantly improved the synthetic efficacy, by providing a practical synthetic process for demethyleneberberine (DMB), columbamine and palmatine. Furthermore, we found that DMB (IC₅₀, 9.06 μM) inhibited the activity of monoamine oxidase B (MAO-B), an enzyme that deaminates dopamine and is particularly involved in the pathology of Parkinson's disease. Besides, columbamine was able to decrease MAO-B activity by approximately 40%. These findings provide perquisites for further in vivo investigation to confirm the therapeutic potentiality of berberine alkaloids, DMB in particular.

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.

Reversible Small Molecule Inhibitors of MAO A and MAO B with Anilide Motifs

BACKGROUND

Ligands consisting of two aryl moieties connected via a short spacer were shown to be potent inhibitors of monoamine oxidases (MAO) A and B, which are known as suitable targets in treatment of neurological diseases. Based on this general blueprint, we synthesized a series of 66 small aromatic amide derivatives as novel MAO A/B inhibitors.

METHODS

The compounds were synthesized, purified and structurally confirmed by spectroscopic methods. Fluorimetric enzymological assays were performed to determine MAO A/B inhibition properties. Mode and reversibility of inhibition was determined for the most potent MAO B inhibitor. Docking poses and pharmacophore models were generated to confirm the in vitro results.

RESULTS

N-(2,4-Dinitrophenyl)benzo[d][1,3]dioxole-5-carboxamide (55, ST-2043) was found to be a reversible competitive moderately selective MAO B inhibitor (IC₅₀ = 56 nM, K_i = 6.3 nM), while N-(2,4-dinitrophenyl)benzamide (7, ST-2023) showed higher preference for MAO A (IC₅₀ = 126 nM). Computational analysis confirmed in vitro binding properties, where the anilides examined possessed high surface complementarity to MAO A/B active sites.

CONCLUSION

The small molecule anilides with different substitution patterns were identified as potent MAO A/B inhibitors, which were active in nanomolar concentrations ranges. These small and easily accessible molecules are promising motifs, especially for newly designed multitargeted ligands taking advantage of these fragments.

Donepezil + chromone + melatonin hybrids as promising agents for Alzheimer's disease therapy

We describe herein the design, multicomponent synthesis and biological studies of new donepezil + chromone + melatonin hybrids as potential agents for Alzheimer's disease (AD) therapy. We have identified compound 14n as promising multitarget small molecule showing strong BuChE inhibition (IC50 = 11.90 ± 0.05 nM), moderate hAChE (IC50 = 1.73 ± 0.34 μM), hMAO A (IC50 = 2.78 ± 0.12 μM), and MAO B (IC50 = 21.29 ± 3.85 μM) inhibition, while keeping a strong antioxidant power (3.04 TE, ORAC test). Consequently, the results reported here support the development of new multitarget Donepezil + Chromone + Melatonin hybrids, such as compound 14n, as a potential drug for AD patients cure.

Dual-target anti-Alzheimer's disease agents with both iron ion chelating and monoamine oxidase-B inhibitory activity

MAO-B leads to an increase in the levels of hydrogen peroxide and oxidative free radicals, which contribute to the aetiology of the AD. Thus, both iron ion chelators and MAO-B inhibitors can be used to treat AD. Taking the coumarin derivatives and hydroxypyridinones as the lead compounds, a series of dual-target hybrids were designed and synthesised by Click Chemistry. The compounds were biologically evaluated for their iron ion chelating and MAO-B inhibitory activity. Most of the compounds displayed excellent iron ion chelating activity and moderate to good anti-MAO-B activity. Compounds 27b and 27j exhibited the most potent MAO-B inhibitory activity, with IC50 values of 0.68 and 0.86 μM, respectively. In summary, these dual-target compounds have the potential anti-AD activity.

HPLC-UV assay for the evaluation of inhibitors of plasma amine oxidase using crude bovine plasma

Recently, we have described a method for evaluation of plasma amine oxidase (PAO) inhibitors, which monitors the formation of 6-(5-phenyl-2H-tetrazol-2-yl)hexanal from the corresponding amine substrate by HPLC with UV-detection using purified bovine PAO. We now investigated, whether crude bovine plasma can be used as enzyme source in this assay instead of the purified enzyme. With the aid of specific inhibitors, it was ensured that there was no detectable activity of other important amine oxidases in the plasma, namely monoamine oxidase (MAO) A and B and diamine oxidase (DAO). For a series of ω-(5-phenyl-2H-tetrazol-2-yl)alkan-1-amine substrates similar conversion rates were measured for both the purified PAO and crude plasma. The inhibition values determined for the PAO inhibitor 2-(4-phenylphenyl)acetohydrazide (16) under different conditions also corresponded. Additionally, inhibition data of the known PAO inhibitor 2-amino-N-(3-phenylbenzyl)acetamide (17) and a newly synthesised meta-substituted derivative of 16 were determined, which together reflect the two-step inhibition mechanism of these covalent inhibitors.

Flurbiprofen-chalcone hybrid Mannich base derivatives as balanced multifunctional agents against Alzheimer's disease: Design, synthesis and biological evaluation

The complex pathogenesis of Alzheimer's disease (AD) calls for multitarget approach for disease management. Herein, a series of novel flurbiprofen-chalcone hybrid Mannich base derivatives were designed and synthesized. The biological screening results indicated that most of the derivatives exhibited potent multi-target effects involved in AD. In particular, compound 6c bearing a pyrrolidine group showed the highest activities against self- and Cu²⁺-induced Aβ_1-42 aggregation (70.65% and 54.89% at 25.0 µM, respectively), highly selective inhibition towards AChE and MAO-B (IC₅₀ = 7.15 μM and 0.43 μM respectively), good antioxidant ability and metal-chelating property. Moreover, 6c displayed excellent anti-neuroinflammatory activity and appropriate BBB permeability in vitro. These outstanding results qualified compound 6c as a promising multifunctional agent for further development of disease-modifying treatment of AD.

1,3,4-Oxadiazol-2-ylbenzenesulfonamides as privileged structures for the inhibition of monoamine oxidase B

The present study investigates the monoamine oxidase (MAO) inhibition properties of a series of ten 5-aryl-1,3,4-oxadiazol-2-ylbenzenesulfonamides. The target compounds were synthesized by dehydration of the corresponding N,N'-diacylhydrazines with phosphorus oxychloride to yield the 1,3,4-oxadiazole cycle with concomitant transformation of the sulfonamide to the sulfonyl chloride group. Treatment with aqueous ammonia in acetonitrile regenerated the target sulfonamides. The results of the enzymology document that these compounds are potent and specific MAO-B inhibitors with the most potent compound exhibiting an IC50 value of 0.0027 µM. An analysis of the structure-activity relationships shows that the 4-benzenesulfonamides are significantly more potent MAO-B inhibitors than the corresponding 3-benzenesulfonamides, and that the corresponding N,N'-diacylhydrazine synthetic precursors are weak MAO inhibitors. Although MAO inhibition by oxadiazole compounds are known, this is the first report of nanomolar MAO inhibition potencies recorded for sulfonamide derivatives. MAO-B specific inhibitors such as those discovered here may be of interest in the treatment of neurodegenerative disorders such as Parkinson's disease.

Discovery and preclinical characterization of [18F]PI-2620, a next-generation tau PET tracer for the assessment of tau pathology in Alzheimer's disease and other tauopathies

PURPOSE

Tau deposition is a key pathological feature of Alzheimer's disease (AD) and other neurodegenerative disorders. The spreading of tau neurofibrillary tangles across defined brain regions corresponds to the observed level of cognitive decline in AD. Positron-emission tomography (PET) has proved to be an important tool for the detection of amyloid-beta (Aβ) aggregates in the brain, and is currently being explored for detection of pathological misfolded tau in AD and other non-AD tauopathies. Several PET tracers targeting tau deposits have been discovered and tested in humans. Limitations have been reported, especially regarding their selectivity.

METHODS

In our screening campaign we identified pyrrolo[2,3-b:4,5-c']dipyridine core structures with high affinity for aggregated tau. Further characterization showed that compounds containing this moiety had significantly reduced monoamine oxidase A (MAO-A) binding compared to pyrido[4,3-b]indole derivatives such as AV-1451.

RESULTS

Here we present preclinical data of all ten fluoropyridine regioisomers attached to the pyrrolo[2,3-b:4,5-c']dipyridine scaffold, revealing compounds 4 and 7 with superior properties. The lead candidate [18F]PI-2620 (compound 7) displayed high affinity for tau deposits in AD brain homogenate competition assays. Specific binding to pathological misfolded tau was further demonstrated by autoradiography on AD brain sections (Braak I-VI), Pick's disease and progressive supranuclear palsy (PSP) pathology, whereas no specific tracer binding was detected on brain slices from non-demented donors. In addition to its high affinity binding to tau aggregates, the compound showed excellent selectivity with no off-target binding to Aβ or MAO-A/B. Good brain uptake and fast washout were observed in healthy mice and non-human primates.

CONCLUSIONS

Therefore, [18F]PI-2620 was selected for clinical validation.

Synthesis of potent neuroprotective butenolides based on plant smoke derived 3,4,5-Trimethylfuran-2(5H)-one and 3-methyl-2H-furo[2,3-c]pyrone-2-one

Smoke derived karrikinolide and trimethylbutenolide exerted neuroprotective effects against monoamine oxidase and acetylcholinesterase. Synthesis of potent analogs was achieved. Sulphur substitution in the bicyclic ring structure of KAR₁ displayed the most encouraging activity returning IC₅₀ values of 13.75 ± 0.001 μM and 0.03 ± 0.02 μM for monoamine oxidase A and B and 0.08 ± 0.006 μM for acetylcholinesterase. Neuroprotective butenolides may be particularly useful in the treatment of depressive disorders, Alzheimer's and Parkinson's diseases.

Design, Synthesis, Docking Studies and Monoamine Oxidase Inhibition of a Small Library of 1-acetyl- and 1-thiocarbamoyl-3,5-diphenyl-4,5-dihydro-(1H)-pyrazoles

New N-acetyl/N-thiocarbamoylpyrazoline derivatives were designed and synthesized in high yields to assess their inhibitory activity and selectivity against human monoamine oxidase A and B. The most important chiral compounds were separated into their single enantiomers and tested. The impact of the substituents at N1, C3 and C5 positions as well the influence of the configuration of the C5 on the biological activity were analyzed. Bulky aromatic groups at C5 were not tolerated. p-Prenyloxyaryl moiety at C3 oriented the selectivity toward the B isoform. The results were also corroborated by molecular modelling studies providing new suggestions for the synthesis of privileged structures to serve as lead compounds for the treatment of mood disorders and neurodegenerative diseases.

Tranylcypromine and 6-trifluoroethyl thienopyrimidine hybrid as LSD1 inhibitor

Tranylcypromine moiety extracted from LSD1 inhibitors and 6-trifluoroethyl thienopyrimidine moiety from menin-MLL1 PPI inhibitors were merged to give new chemotypes for medicinal chemistry study. Among 15 new compounds prepared in this work, some exhibited nanomolar LSD1 activity and good selectivity over MAO-A/B, low micromolar menin-MLL1 PPI inhibitory activity, as well as submicromolar MV4-11 antiprofilative activities. Intracellular LSD1 engagement of compounds with higher enzymatic and antiproliferative activities was confirmed by CD86 mRNA up-regulation experiments.

"In-loop" [11 C]CO2 fixation: Prototype and proof of concept

Carbon-11-labeled carbon dioxide is the most common feedstock for the synthesis of positron emission tomography radiotracers and can be directly used for 11 C-carbonylation. Herein, we report the development of an apparatus that takes advantage of "in-loop" technologies to facilitate robust and reproducible syntheses of 11 C-carbonyl-based radiotracers by [11 C]CO2 -fixation. Our "in-loop" [11 C]CO2 -fixation method is simple, efficient, and proceeds smoothly at ambient pressure and temperature. We selected model 11 C-carbonyl-labeled carbamates as well as symmetrical and unsymmetrical ureas based on their widespread use in radiotracer design and our clinical research interests for proof of concept. Utility of this method is demonstrated by the synthesis of a reversible radiopharmaceutical for monoamine oxidase B, [11 C]SL25.1188, and 2 novel fatty acid amide hydrolase inhibitors. These radiotracers were isolated and formulated (>3.5 GBq; 100 mCi) with radiochemical purities (>99%) and molar radioactivity (≥80 GBq/μmol; ≥2162 mCi/μmol).

Synthesis and Biological Evaluation of New Thiosemicarbazone Derivative Schiff Bases as Monoamine Oxidase Inhibitory Agents

Twenty-six novel thiosemicarbazone derivative B1–B26 were synthesized via condensation reactions between the corresponding thiosemicarbazides and aldehydes. The chemical characterization of the compounds was carried out by infrared (IR), mass (MS), proton and carbon nuclear magnetic resonance (¹H- and ¹³C-NMR) spectroscopic analyses. The compounds were investigated for their monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B) inhibitory activity and most of them were more potent against MAO-A enzyme when compared with MAO-B enzyme. N-Cyclohexyl-2-[4-[(4-chlorophenyl)thio]benzylidene]hydrazine-1-carbothioamide (B24) was the most active compound against MAO-A. The enzyme kinetics study revealed that compound B24 has a reversible and competitive mode of binding. Interaction modes between compound B24 and MAO-A were clarified by docking studies. In addition, the favourable absorption, distribution, metabolism, and excretion (ADME) properties and non-toxic nature of compound B24 make this compound a promising MAO-A inhibitor.

Design and Synthesis of New Benzothiazole Compounds as Selective hMAO-B Inhibitors

In the current work a new class of novel benzothiazole-hydrazone derivatives was designed and synthesized as hMAO-B inhibitors. Structures of the obtained compounds (3a-3j) were characterized by IR, ¹H-NMR, 13C-NMR, and HRMS spectroscopic methods. The inhibitory activity of compounds (3a-3j) against hMAO-A and hMAO-B enzymes was evaluated by using an in vitro fluorometric method. According to activity results, some of the synthesized compounds displayed selective and significant hMAO-B enzyme inhibitor activity. Compound 3e was the most active derivative in the series with an IC50 value of 0.060 µM. Furthermore, cytotoxicity of compound 3e was investigated and found to be non-cytotoxic. Absorption, distribution, metabolism, and excretion (ADME) and blood-brain barrier (BBB) permeability predictions were performed for all compounds. It was determined that these compounds may have a good pharmacokinetic profiles. Bınding modes between the most active compound 3e and the hMAO-B enzyme were analyzed by docking studies. It was observed that there is a strong interaction between compound 3e and enzyme active site.

Synthesis of New Hydrazone Derivatives for MAO Enzymes Inhibitory Activity

In the present work, 14 new 1-substituted-2-phenylhydrazone derivatives were synthesized to evaluate their inhibitory activity against hMAO enzymes. The structures of the newly synthesized hydrazones 2a–2n were characterized by IR, ¹H-NMR, ¹³C-NMR, HR-MS spectroscopic methods. The inhibitory activity of compounds 2a–2n against hMAO-A and hMAO-B enzymes was elucidated by using an in-vitro Amplex Red^® reagent assay based on fluorometric methods. According to the activity studies, 2a and 2b were found to be the most active compounds against hMAO-A enzyme, with IC₅₀ values of 0.342 µM and 0.028 µM, respectively. The most active compounds 2a–2b were evaluated by means of enzyme kinetics and docking studies. Moreover, these compounds were subjected to cytotoxicity and genotoxicity tests to establish their preliminary toxicological profiles and were found to be non-cytotoxic and non-genotoxic. Consequently, the findings of this study display the biological importance of compounds 2a, 2b as selective, irreversible and competitive inhibitors of hMAO-A. Docking studies revealed that there is a strong interaction between hMAO-A and the most active compound 2b.

Structure-Based Design and Synthesis of Harmine Derivatives with Different Selectivity Profiles in Kinase versus Monoamine Oxidase Inhibition

Dual-specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A) is an emerging biological target with implications in diverse therapeutic areas such as neurological disorders (Down syndrome, in particular), metabolism, and oncology. Harmine, a natural product that selectively inhibits DYRK1A amongst kinases, could serve as a tool compound to better understand the biological processes that arise from DYRK1A inhibition. On the other hand, harmine is also a potent inhibitor of monoamine oxidase A (MAO-A). Using structure-based design, we synthesized a collection of harmine analogues with tunable selectivity toward these two enzymes. Modifications at the 7-position typically decreased affinity for DYRK1A, whereas substitution at the 9-position had a similar effect on MAO-A inhibition but DYRK1A inhibition was maintained. The resulting collection of compounds can help to understand the biological role of DYRK1A and also to assess the interference in the biological effect originating in MAO-A inhibition.

Synthesis and Evaluation of Phenylxanthine Derivatives as Potential Dual A2AR Antagonists/MAO-B Inhibitors for Parkinson's Disease

The aim of this research was to prove the speculation that phenylxanthine (PX) derivatives possess adenosine A2A receptor (A2AR)-blocking properties and to screening and evaluate these PX derivatives as dual A2AR antagonists/MAO-B inhibitors for Parkinson′s disease. To explore this hypothesis, two series of PX derivatives were prepared and their antagonism against A2AR and inhibition against MAO-B were determined in vitro. In order to evaluate further the antiparkinsonian properties, pharmacokinetic and haloperidol-induced catalepsy experiments were carried out in vivo. The PX-D and PX-E analogues acted as potent A2AR antagonists with Ki values ranging from 0.27 to 10 μM, and these analogues displayed relatively mild MAO-B inhibition potencies, with inhibitor dissociation constants (Ki values) ranging from 0.25 to 10 μM. Further, the compounds PX-D-P6 and PX-E-P8 displayed efficacious antiparkinsonian properties in haloperidol-induced catalepsy experiments, verifying that these two compounds were potent A2AR antagonists and MAO-B inhibitors. We conclude that PX-D and PX-E analogues are a promising candidate class of dual-acting compounds for treating Parkinson′s disease.

N-Propargylpiperidines with naphthalene-2-carboxamide or naphthalene-2-sulfonamide moieties: Potential multifunctional anti-Alzheimer's agents

In the brains of patients with Alzheimer's disease, the enzymatic activities of butyrylcholinesterase (BChE) and monoamine oxidase B (MAO-B) are increased. While BChE is a viable therapeutic target for alleviation of symptoms caused by cholinergic hypofunction, MAO-B is a potential therapeutic target for prevention of neurodegeneration in Alzheimer's disease. Starting with piperidine-based selective human (h)BChE inhibitors and propargylamine-based MAO inhibitors, we have designed, synthesized and biochemically evaluated a series of N-propargylpiperidines. All of these compounds inhibited hBChE with good selectivity over the related enzyme, acetylcholinesterase, and crossed the blood-brain barrier in a parallel artificial membrane permeation assay. The crystal structure of one of the inhibitors (compound 3) in complex with hBChE revealed its binding mode. Three compounds (4, 5, 6) showed concomitant inhibition of MAO-B. Additionally, the most potent hBChE inhibitor 7 and dual BChE and MAO-B inhibitor 6 were non-cytotoxic and protected neuronal SH-SY5Y cells from toxic amyloid β-peptide species.

Drugs related to monoamine oxidase activity

Progress in understanding the role of monoamine neurotransmission in pathophysiology of neuropsychiatric disorders was made after the discovery of the mechanisms of action of psychoactive drugs, including monoamine oxidase (MAO) inhibitors. The increase in monoamine neurotransmitter availability, decrease in hydrogen peroxide production, and neuroprotective effects evoked by MAO inhibitors represent an important approach in the development of new drugs for the treatment of mental disorders and neurodegenerative diseases. New drugs are synthesized by acting as multitarget-directed ligands, with MAO, acetylcholinesterase, and iron chelation as targets. Basic information is summarized in this paper about the drug-induced regulation of monoaminergic systems in the brain, with a focus on MAO inhibition. Desirable effects of MAO inhibition include increased availability of monoamine neurotransmitters, decreased oxidative stress, decreased formation of neurotoxins, induction of pro-survival genes and antiapoptotic factors, and improved mitochondrial functions.

Design, synthesis and evaluation of novel dual monoamine-cholinesterase inhibitors as potential treatment for Alzheimer's disease

Current novel therapeutic approach suggests that multifunctional compounds with diverse biological properties and a single bioavailability and pharmacokinetic metabolism, will produce higher significant advantages in treatment of neurodegenerative diseases, such as Alzheimer's disease (AD). Based on this rational, a new class of cholinesterase (ChE)-monoamine oxidase (MAO) inhibitors were designed and synthesized by amalgamating the propargyl moiety of the irreversible selective MAO-B inhibitor, neuroprotective/neurorestorative anti-Parkinsonian drug, rasagiline, into the "N-methyl" position of the ChE inhibitor, anti-AD drug rivastigmine. Initially, we examined the MAO and ChE inhibitory effect of these novel compounds, MT series in vitro and in vivo. Among MT series, MT-031 exhibited higher potency as a dual MAO-A and ChE inhibitor compared to other compounds in acute-treated mice. Additionally, MT-031 was found to increase the striatal levels of dopamine (DA), serotonin (5-HT) and norepinephrine (NE), and prevent the metabolism of DA and 5-HT. Finally, we have demonstrated that MT-031 exerted neuroprotective effect against H2O2-induced neurotoxicity and reactive oxygen species generation in human neuroblastoma SH-SY5Y cells. These findings provide evidence that MT-031 is a potent brain permeable novel multifunctional, neuroprotective and MAO-A/ChE inhibitor, preserves in one molecule entity some of the beneficial properties of its parent drugs, rasagiline and rivastigmine, and thus may be indicated as novel therapeutic approach for AD.

Searching for Multi-Targeting Neurotherapeutics against Alzheimer's: Discovery of Potent AChE-MAO B Inhibitors through the Decoration of the 2H-Chromen-2-one Structural Motif

The need for developing real disease-modifying drugs against neurodegenerative syndromes, particularly Alzheimer’s disease (AD), shifted research towards reliable drug discovery strategies to unveil clinical candidates with higher therapeutic efficacy than single-targeting drugs. By following the multi-target approach, we designed and synthesized a novel class of dual acetylcholinesterase (AChE)-monoamine oxidase B (MAO-B) inhibitors through the decoration of the 2H-chromen-2-one skeleton. Compounds bearing a propargylamine moiety at position 3 displayed the highest in vitro inhibitory activities against MAO-B. Within this series, derivative 3h emerged as the most interesting hit compound, being a moderate AChE inhibitor (IC₅₀ = 8.99 µM) and a potent and selective MAO-B inhibitor (IC₅₀ = 2.8 nM). Preliminary studies in human neuroblastoma SH-SY5Y cell lines demonstrated its low cytotoxicity and disclosed a promising neuroprotective effect at low doses (0.1 µM) under oxidative stress conditions promoted by two mitochondrial toxins (oligomycin-A and rotenone). In a Madin-Darby canine kidney (MDCK)II-MDR1 cell-based transport study, Compound 3h was able to permeate the BBB-mimicking monolayer and did not result in a glycoprotein-p (P-gp) substrate, showing an efflux ratio = 0.96, close to that of diazepam.

Synthesis and evaluation of selegiline derivatives as monoamine oxidase inhibitor, antioxidant and metal chelator against Alzheimer's disease

A series of compounds with monoamine oxidase inhibition and biometal chelation activities were designed, synthesised and evaluated as agents against Alzheimer's disease. The in vitro assay shows that most target compounds exhibit good MAO-B activities with submicromolar IC50 values and antioxidant activity (1.49-5.67 ORAC-FL values). The selected compounds were used to determine the biometal chelating ability using UV-vis spectrometry and high-resolution mass spectrometry, which confirm that they can effectively interact with copper(II), iron(II) and zinc(II). The ThT fluorescence binding assay indicates that the synthetic compounds can inhibit Cu(II)-induced Aβ1-42 aggregation. The parallel artificial membrane permeation assay shows that most target compounds can cross the BBB. Based on these results, compound 8a was selected as a potential multifunctional agent for the treatment of AD.

Structure-based design and analysis of MAO-B inhibitors for Parkinson's disease: using in silico approaches

Parkinson's disease (PD) is a degenerative disorder of the CNS, characterized by cerebral depletion of dopamine (DA), hence one of the approaches to delay the depletion of DA is to inhibit its oxidative deamination. Monoamine oxidases (MAO) carry out the oxidative deamination of monoamines like DA. These are intracellular enzymes, located on the outer mitochondrial membrane. MAO-A and MAO-B are the two subtypes of which MAO-B is the most predominant enzyme and is commonly found in the brain. Inhibition of the MAO-B enzyme boosts the effect of both endogenous and exogenous DA. In this study, we have carried out crystal structure analysis and structure-based design of MAO-B inhibitors. We also performed molecular dynamics, flexible docking, induced-fit docking and ADME prediction of the newly designed compounds.

Combining QSAR classification models for predictive modeling of human monoamine oxidase inhibitors

Due to their role in the metabolism of monoamine neurotransmitters, MAO-A and MAO-B present a significant pharmacological interest. For instance the inhibitors of human MAO-B are considered useful tools for the treatment of Parkinson Disease. Therefore, the rational design and synthesis of new MAOs inhibitors is considered of great importance for the development of new and more effective treatments of Parkinson Disease. In this work, Quantitative Structure Activity Relationships (QSAR) has been developed to predict the human MAO inhibitory activity and selectivity. The first step was the selection of a suitable dataset of heterocyclic compounds that include chromones, coumarins, chalcones, thiazolylhydrazones, etc. These compounds were previously synthesized in one of our laboratories, or elsewhere, and their activities measured by the same assays and for the same laboratory staff. Applying linear discriminant analysis to data derived from a variety of molecular representations and feature selection algorithms, reliable QSAR models were built which could be used to predict for test compounds the inhibitory activity and selectivity toward human MAO. This work also showed how several QSAR models can be combined to make better predictions. The final models exhibit significant statistics, interpretability, as well as displaying predictive power on an external validation set made up of chromone derivatives with unknown activity (that are being reported here for first time) synthesized by our group, and coumarins recently reported in the literature.

[Design of acetylcholinesterase inhibitor for Alzheimer's disease therapy: from multi-binding site inhibitors to multi-target directed ligands]

Alzheimer's disease (AD) is a complex neurodegenerative disorder which seriously causes the dementia in elderly people and afflicts millions of people worldwide. Drug discovery for Alzheimer's disease therapy has been a hot research area and a big challenge, in which development of acetylcholinesterase (AChE) inhibitors design was the most active and some AChE inhibitors are commercially available for AD medication already. However, practical using of commercial AChE inhibitors showed their limited usefulness and related adverse effects. Thus, it is extremely urgent to find novel AChE inhibitors with higher potency and less adverse effects. Based on the accurate crystallographic studies about AChE, strategies for multi-binding site AChE inhibitors have been formed, followed by design of the multi-target directed ligands. In this review, the structures and binding modes of commercial AChE inhibitors were briefly discussed, together with the development of AChE inhibitor design for AD therapy: from multi-binding site inhibitors to multi-target directed ligands.

Inhibition of monoamine oxidase by C5-substituted phthalimide analogues

Literature reports that isatin as well as C5- and C6-substituted isatin analogues are reversible inhibitors of human monoamine oxidase (MAO) A and B. In general, C5- and C6-substitution of isatin leads to enhanced binding affinity to both MAO isozymes compared to isatin and in most instances result in selective binding to the MAO-B isoform. Crystallographic and modeling studies suggest that the isatin ring binds to the substrate cavities of MAO-A and -B and is stabilized by hydrogen bond interactions between the NH and the C2 carbonyl oxygen of the dioxoindolyl moiety and water molecules present in the substrate cavities of MAO-A and -B. Based on these observations and the close structural resemblances between isatin and its phthalimide isomer, a series of phthalimide analogues were synthesized and evaluated as MAO inhibitors. While phthalimide and N-aryl-substituted phthalimides were found to be weak MAO inhibitors, phthalimide homologues containing C5 substituents were potent reversible inhibitors of recombinant human MAO-B with IC(50) values ranging from 0.007 to 2.5 μM and moderately potent reversible inhibitors of recombinant human MAO-A with IC(50) values ranging from 0.22 to 9.0 μM. By employing molecular docking the importance of hydrogen bonding between the active sites of MAO-A and -B and the phthalimide inhibitors are highlighted.

Synthesis and Monoamine Oxidase Inhibitory Activity of New Pyridazine-, Pyrimidine- and 1,2,4-Triazine-Containing Tricyclic Derivatives

A number of condensed azines, mostly belonging to the families of indeno-fused pyridazines (1), pyrimidines (2, 3), and 1,2,4-triazines (4, 5), were synthesized and evaluated in vitro as monoamine oxidase (MAO) A and B inhibitors. Most of them showed higher inhibition potency toward MAO-B, the most effective one being 3-(3-nitrophenyl)-9H-indeno[1,2-e] [1,2,4]triazin-9-one (4c), which displayed an IC50 value of 80 nM and proved to be 10-fold more potent than its [2,1-e] fusion isomer 5. Replacing the 3-phenyl group of the known indeno[1,2-c]pyridazin-5-one MAO-B inhibitors with a flexible phenoxymethyl group enhanced the inhibitory potency. The inhibition data highlighted the importance of the aza-heterocyclic scaffold in affecting the MAO isoform selectivity. The 3-phenyl derivatives with type 1, 4, and 5 scaffolds were inhibitors of MAO-B with little or no MAO-A effect, whereas 2- or 3-phenyl derivatives of type 2 and 3 pyrimidine-containing fusion isomers inhibited both isoenzymes with a structure-dependent preference toward MAO-A.

Solid-Phase Synthesis and Insights into Structure−Activity Relationships of Safinamide Analogues as Potent and Selective Inhibitors of Type B Monoamine Oxidase

Safinamide, (S)-N2-{4-[(3-fluorobenzyl)oxy]benzyl}alaninamide methanesulfonate, which is in phase III clinical trials as an anti-Parkinson drug, and a library of alkanamidic analogues were prepared through an expeditious solid-phase synthesis and evaluated for their monoamine oxidase B (MAO-B) and monoamine oxidase A (MAO-A) inhibitory activity and selectivity. (S)-3-Chlorobenzyloxyalaninamide (8) and (S)-3-chlorobenzyloxyserinamide (13) derivatives proved to be more potent MAO-B inhibitors than safinamide (IC50 = 33 and 43 nM, respectively, vs 98 nM) but with a lower MAO-B selectivity (SI = 3455 and 1967, respectively, vs 5918). The highest MAO-B inhibitory potency (IC50 = 17 nM) and a good selectivity (SI = 2941) were displayed by (R)-21, a tetrahydroisoquinoline analogue of safinamide. Structure-affinity relationships and docking simulations pointed out strong negative steric effects of alpha-aminoamide side chains and para substituents of the benzyloxy groups and favorable hydrophobic interactions of meta substituents. The significantly diverse MAO-B affinities of a number of R and S alpha-aminoamide enantiomers, including the two rigid analogues (21) of safinamide, indicated likely enantioselective interactions at the enzymatic binding sites.

A new therapeutic approach in Alzheimer disease: some novel pyrazole derivatives as dual MAO-B inhibitors and antiinflammatory analgesics

The increasing life expectancy in our population makes Alzheimer's disease (AD) a growing public health problem. There is a great need to find a way to prevent and delay the disease. It was shown that monoamine oxidase-B (MAO-B) inhibitors and antiinflammatory agents might be effective in treating AD. Therefore, a novel series of 1-thiocarbamoyl-3-substituted phenyl-5-(2-pyrrolyl)-4,5-dihydro-(1H)-pyrazole derivatives as promising MAO-B inhibitors was synthesized and investigated for the ability to inhibit selectively the activity of the A and B isoforms of monoamine oxidase (MAO). Most of the synthesized compounds showed high activity against both the MAO-A (compounds 3e-3h) and the MAO-B (compounds 3i-3l) isoforms. All the synthesized compounds were also tested for their in vivo antiinflammatory activity by two different bioassays namely, carrageenan-induced oedema and acetic acid-induced increase in capillary permeability in mice. In addition, analgesic and ulcerogenic activities were determined. The combined antiinflammatory data from in vivo animal models showed that compound 3k exhibited anti-inflammatory activity comparable to that of indomethacin with no ulcerogenic effects. Since compound 3k exhibits both antiinflammatory-analgesic activity and MAO-B inhibition, it needs further detailed studies.

Monoamine oxidase isoform-dependent tautomeric influence in the recognition of 3,5-diaryl pyrazole inhibitors

A series of 3,5-diaryl pyrazoles were prepared and assayed for their ability to inhibit reversibly monoamine oxidase-A (MAO-A) and monoamine oxidase B (MAO-B). Several compounds show inhibitory activity with concentration values in the nanomolar range. A computational work was carried out on the two most selective inhibitors that have tautomeric pyrazole forms. The binding free energies of these compounds for each MAO isoform were influenced by the tautomeric equilibria.

New pyrrole inhibitors of monoamine oxidase: synthesis, biological evaluation, and structural determinants of MAO-A and MAO-B selectivity

A series of new pyrrole derivatives have been synthesized and evaluated for their monoamine oxidase (MAO) A and B inhibitory activity and selectivity. N-Methyl,N-(benzyl),N-(pyrrol-2-ylmethyl)amine (7) and N-(2-benzyl),N-(1-methylpyrrol-2-ylmethyl)amine (18) were the most selective MAO-B (7, SI = 0.0057) and MAO-A (18, SI = 12500) inhibitors, respectively. Docking and molecular dynamics simulations gave structural insights into the MAO-A and MAO-B selectivity. Compound 18 forms an H-bond with Gln215 through its protonated amino group into the MAO-A binding site. This H-bond is absent in the 7/MAO-A complex. In contrast, compound 7 places its phenyl ring into an aromatic cage of the MAO-B binding pocket, where it forms charge-transfer interactions. The slightly different binding pose of 18 into the MAO-B active site seems to be forced by a bulkier Tyr residue, which replaces a smaller Ile residue present in MAO-A.

Selective Inhibitory Activity against MAO and Molecular Modeling Studies of 2-Thiazolylhydrazone Derivatives

A series of 2-thiazolylhydrazone derivatives have been investigated for the ability to inhibit the activity of the A and B isoforms of monoamine oxidase (MAO) selectively. All of the compounds showed high activity against both the MAO-A and the MAO-B isoforms with pKi values ranging between 5.92 and 8.14 for the MAO-A and between 4.69 and 9.09 for the MAO-B isoforms. Both the MAO-A and the MAO-B isoforms, deposited in the Protein Data Bank as model 2BXR and 1GOS, respectively, were considered in a computational study performed with docking techniques on the most active and MAO-B-selective inhibitor, 18.

New carbon-linked azole oxazolidinones with improved potency and pharmacokinetics

Substitution of phenyl oxazolidinones with carbon-linked azoles resulted in the discovery of a new class of potent oxazolidinones that have excellent Gram-positive activity. In addition, replacement of the C-5 acetamide side chains with a 4-methyl triazole diminished monoamine oxidase activity. The synthesis and biological evaluation of these compounds are reported.

3-[5-(4,5-dihydro-1H-imidazol-2-yl)-furan-2-yl]phenylamine (Amifuraline), a promising reversible and selective peripheral MAO-A inhibitor

On the basis of the observation that the central side effects of MAO inhibitors may represent a major limit for their use in pathological processes involving peripheral MAOs, we investigated the possibility of generating novel inhibitors able to target specifically peripheral MAOs. To address this issue, we designed compounds 7-28. From biological results, the 2-(5-phenyl-furan-2-yl)-4,5-dihydro-1H-imidazole (Furaline, 17) proved to be a suitable lead. In fact, in enzyme assays on homogenate preparation from rat liver and HEK cells expressing MAO-A or MAO-B, compounds possessing the frame of 17 behaved as selective and reversible MAO-A inhibitors. Interestingly, in in vivo studies the amino derivative 21 (Amifuraline), endowed with good hydrophilic character, was able to significantly inhibit liver but not brain MAO-A.

Impact of Species-Dependent Differences on Screening, Design, and Development of MAO B Inhibitors

The impact of species-dependent differences between human and rat MAO B on inhibitor screening was evidenced for two classes of compounds, coumarin and 5H-indeno[1,2-c]pyridazin-5-one derivatives. All examined compounds have shown a greater inhibitor potency toward human MAO B than toward rat MAO B. Moreover, no correlation was found between human and rat pIC(50) values. These divergences have important implications for the design and development of drugs involved in the MAO B metabolic pathway, suggesting that results obtained using rat enzyme cannot be extrapolated to human CNS, a priori. Indeed, the selection of a hit compound for lead generation could be different using human rather than rat enzyme. Moreover, the influence of substituents on the in vitro inhibition of human MAO B was markedly different between homogeneous series of coumarin and 5H-indeno[1,2-c]pyridazin-5-one derivatives, suggesting different binding modes, a hypothesis clearly supported by molecular docking simulations of inhibitors into the active site of human MAO B.

Structural Insights into Monoamine Oxidase Inhibitory Potency and Selectivity of 7-Substituted Coumarins from Ligand- and Target-Based Approaches

A new series of 3-, 4-, 7-polysubstituted coumarins have been designed and evaluated for their monoamine oxidase A and monoamine oxidase B (MAO-A and MAO-B) inhibitory potency. Substituents at position 7 consisted of a bridge of different physicochemical nature linking a phenyl ring to the coumarin scaffold. Structure-affinity and structure-selectivity relationships, derived through CoMFA-GOLPE and docking studies, revealed the key physicochemical interactions responsible for the observed MAO-B and MAO-A inhibitory potency and suggested the main structural determinants for high selectivity toward one of the two enzymatic isoforms. The predictive power of our models was proved with the design of a new inhibitor demonstrating an outstanding MAO-B affinity (pIC50 = 8.29) and the highest MAO-B selectivity (DeltapIC50 = 3.39) within the entire series of ligands examined herein.

Synthesis, molecular modeling studies, and selective inhibitory activity against monoamine oxidase of N,N'-bis[2-oxo-2H-benzopyran]-3-carboxamides

A novel series of N,N'-bis[2-oxo-2H-1-benzopyran]-3-carboxamide derivatives have been synthesized and investigated for the ability to inhibit the activity of the A and B isoforms of monoamine oxidase (MAO). Some of the synthesized compounds show good selective inhibitory activity against the MAO-A isoform. Both the MAO-A and -B isoforms, deposited in the Protein Data Bank as the 2BXR and 1GOS models, respectively, were considered in a computational study performed with docking techniques on the most active and selective inhibitors.

Synthesis, Structural Reassignment, and Biological Activity of Type B MAO Inhibitors Based on the 5H-Indeno[1,2-c]pyridazin-5-one Core

The synthesis and enzyme inhibitor properties of reversible type B monoamine oxidase inhibitors are described. These compounds belong to the 5H-indeno[1,2-c]pyridazine family and possess a hydrophobic benzyloxy or 4,4,4-trifluorobutoxy side chain which, in contrast to a previous assignment, has been unambiguously located at C(8) of the heterocyclic moiety. Investigation of the regioisomeric structures establishes that substitution of the 5H-indeno[1,2-c]pyridazin-5-one core at C(7) vs C(8) dramatically influences the MAO-inhibiting properties of these compounds.

Synthesis, Biological Evaluation and 3D-QSAR of 1,3,5-Trisubstituted-4,5- Dihydro-(1H)-Pyrazole Derivatives as Potent and Highly Selective Monoamine Oxidase A Inhibitors

The present report provides a extended study of the chemistry, the inhibitory activity against monoamino oxidases (MAO), and molecular modeling including the 3D-QSAR hypothesis of 1,3,5-trisubstituted-4,5-dihydro-(1H)-pyrazole derivatives. Four series of about eighty novel pyrazoline derivatives were prepared and investigated for their ability to inhibit the activity of the A and B isoforms of MAO selectively. Most of the new synthesized compounds proved more reversible, potent, and selective inhibitors of MAO-A than of MAO-B, and could be taken into account to develop the search further in this field, knowing that reversible and selective MAO-A inhibitors are used as antidepressant and antianxiety drug. The 30 most active compounds show inhibitory activity on MAO-A in the 8.6 x 10(-8) - 9.0 x 10(-9)M range. Moreover, it should be pointed out that for most of them a high IC(50) > or = 10(-9)M value is associated with a high A-selectivity (Selectivity Index MAO-B/MAO-A in the 10,000-16,250 range). Furthermore, due to the presence of a chiral centre at the C5 position of the pyrazole moiety, we performed the semi-preparative chromatographic enantioseparation of the most potent, selective, and chiral compounds. The separated enantiomers were then submitted to in vitro biological evaluation, and from the results of these experiments it has been possible to point out a difference in inhibiting the two isoforms selectively between the racemic mixture and the single enantiomers. The molecular modeling work was carried out combining the Glide docking approach with CoMFA with the aim to rationalize the structure-activity relationships of each pyrazoline inhibitor toward MAO-A and MAO-B isoforms and to derive a suitable selectivity model.

Synthesis of 3-benzyl-2-substituted quinoxalines as novel monoamine oxidase A inhibitors

A new series of 3-benzyl-2-substituted quinoxalines have been synthesized by means of microwave enhancement of nucleophilic substitution reaction involving the corresponding 2-chloroquinoxaline analogs and substituted amines or hydrazine. The synthesized compounds were evaluated for their monoamine oxidase A and B inhibitory activity by determination of their IC(50). All the newly synthesized compounds showed more selective inhibitory activity toward MAO-A than MAO-B. In addition, the acute toxicity of the synthesized compounds was determined. This work may be a fruitful matrix of the synthesis of a new series of novel MAO-A inhibitors with good safety margins.