Monoamine oxidase inhibition by selected dye compounds

Monoamine oxidase (MAO) is an important drug target as the MAO isoforms play key roles in neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease, as well as in neuropsychiatric diseases such as depression. Methylene blue is an inhibitor of MAO‐A, while azure B, the major metabolite of methylene blue, and various other structural analogues retain the ability to inhibit MAO‐A. Based on this, the present study evaluated 22 dyes, many of which are structurally related to methylene blue, as potential inhibitors of human MAO‐A and MAO‐B. The results highlighted three dye compounds as good potency competitive and reversible MAO inhibitors, and which exhibit higher MAO inhibition than methylene blue: acridine orange, oxazine 170 and Darrow red. Acridine orange was found to be a MAO‐A specific inhibitor (IC₅₀ = 0.017 μM), whereas oxazine 170 is a MAO‐B specific inhibitor (IC₅₀ = 0.0065 μM). Darrow red was found to be a non‐specific MAO inhibitor (MAO‐A, IC₅₀ = 0.059 μM; MAO‐B, IC₅₀ = 0.065 μM). These compounds may be advanced for further testing and preclinical development, or be used as possible lead compounds for the future design of MAO inhibitors.     

The Synthesis and Evaluation of C7‐Substituted α‐Tetralone Derivatives as Inhibitors of Monoamine Oxidase

Based on a previous report that α‐tetralone (3,4‐dihydro‐2H‐naphthalen‐1‐one) is a promising scaffold for the design of highly potent inhibitors of the enzyme, monoamine oxidase, the present study investigates the monoamine oxidase inhibitory properties of a synthetic series of fifteen C7‐substituted α‐tetralone derivatives. Arylalkyloxy substitution on C7 of the α‐tetralone moiety yielded compounds with high inhibition potencies toward the human monoamine oxidase‐B isoform with all compounds possessing IC₅₀ values in the submicromolar range (0.00089–0.047 μm ). The C7‐substituted α‐tetralones also were highly potent monoamine oxidase‐A inhibitors with thirteen (of fifteen) compounds possessing IC₅₀ values in the submicromolar range (0.010–0.741 μm ). The α‐tetralones were, however, in each instance selective for monoamine oxidase‐B over the monoamine oxidase‐A isoform. Dialyses of enzyme–inhibitor mixtures show that, while a representative inhibitor acts as a reversible monoamine oxidase‐A inhibitor, inhibition of monoamine oxidase‐B is not readily reversed by dialysis. Using a molecular modeling approach, possible binding orientations and interactions of selected α‐tetralones with the active sites of the monoamine oxidases are also proposed. This study suggests that C7‐substituted α‐tetralones are promising monoamine oxidase inhibitors and may represent lead compounds for the development of therapies for Parkinson's disease and depression.     

Beyond Topoisomerase Inhibition: Antitumor 1,4‐Naphthoquinones as Potential Inhibitors of Human Monoamine Oxidase

Monoamine oxidase (MAO) action has been involved in the regulation of neurotransmitters levels, cell signaling, cellular growth, and differentiation as well as in the balance of the intracellular polyamine levels. Although so far obscure, MAO inhibitors are believed to have some effect on tumors progression. 1,4‐naphthoquinone (1,4‐NQ) has been pointed out as a potential pharmacophore for inhibition of both MAO and DNA topoisomerase activities, this latter associated with antitumor activity. Herein, we demonstrated that certain antitumor 1,4‐NQs, including spermidine‐1,4‐NQ, lapachol, and nor‐lapachol display inhibitory activity on human MAO‐A and MAO‐B. Kinetic studies indicated that these compounds are reversible and competitive MAO inhibitors, being the enzyme selectivity greatly affected by substitutions on 1,4‐NQ ring. Molecular docking studies suggested that the most potent MAO inhibitors are capable to bind to the MAO active site in close proximity of flavin moiety. Furthermore, ability to inhibit both MAO‐A and MAO‐B can be potentialized by the formation of hydrogen bonds between these compounds and FAD and/or the residues in the active site. Although spermidine‐1,4‐NQs exhibit antitumor action primarily by inhibiting topoisomerase via DNA intercalation, our findings suggest that their effect on MAO activity should be taken into account when their application in cancer therapy is considered.     

Structure–activity relationship studies of benzyl‐, phenethyl‐, and pyridyl‐substituted tetrahydroacridin‐9‐amines as multitargeting agents to treat Alzheimer's disease

A library of substituted tetrahydroacridin‐9‐amine derivatives were designed, synthesized, and evaluated as dual cholinesterase and amyloid aggregation inhibitors. Compound 8e (N‐(3,4‐dimethoxybenzyl)‐1,2,3,4‐tetrahydroacridin‐9‐amine) was identified as a potent inhibitor of butyrylcholinesterase (BuChE IC₅₀ = 20 nm ; AChE IC₅₀ = 2.2 μm ) and was able to inhibit amyloid aggregation (40% inhibition at 25 μm ). Compounds 9e (6‐chloro‐N‐(3,4‐dimethoxybenzyl)‐1,2,3,4‐tetrahydroacridin‐9‐amine, AChE IC₅₀ = 0.8 μm ; BuChE IC₅₀ = 1.4 μm ; Aβ‐aggregation inhibition = 75.7% inhibition at 25 μm ) and 11b (6‐chloro‐N‐(3,4‐dimethoxyphenethyl)‐1,2,3,4‐tetrahydroacridin‐9‐amine, AChE IC₅₀ = 0.6 μm ; BuChE IC₅₀ = 1.9 μm ; Aβ‐aggregation inhibition = 85.9% inhibition at 25 μm ) were identified as the best compounds with dual cholinesterase and amyloid aggregation inhibition. The picolylamine‐substituted compound 12c (6‐chloro‐N‐(pyridin‐2‐ylmethyl)‐1,2,3,4‐tetrahydroacridin‐9‐amine) was the most potent AChE inhibitor (IC₅₀ = 90 nm ). These investigations demonstrate the utility of 3,4‐dimethoxyphenyl substituent as a novel pharmacophore possessing dual cholinesterase inhibition and anti‐Aβ‐aggregation properties that can be used in the design and development of small molecules with multitargeting ability to treat Alzheimer's disease.     

Optimization of pyrrolo[3,4-f]indole-5,7-dione and indole-5,6-dicarbonitrile derivatives as inhibitors of monoamine oxidase

In recent studies, we have investigated the monoamine oxidase (MAO) inhibition properties of pyrrolo[3,4-f]indole-5,7-dione and indole-5,6-dicarbonitrile derivatives. Since numerous high potency MAO inhibitors are present among these chemical classes, the present study synthesizes 44 additional derivatives in an attempt to further derive structure-activity relationships (SARs) and to establish optimal substitution patterns for MAO inhibition. The results show that, with the exception of one compound, all indole-5,6-dicarbonitrile derivatives (10) exhibit submicromolar IC₅₀ values for the inhibition of MAO, with the most potent MAO-A inhibitor exhibiting an IC₅₀ value of 0.006 μM while the most potent MAO-B inhibitor exhibits an IC₅₀ value of 0.058 μM. Interestingly, an N-oxide derivative ( 4c ) also proved to be a potent and nonspecific MAO inhibitor. With the exception of one compound, all of the pyrrolo[3,4-f]indole-5,7-diones (28) also exhibit submicromolar IC₅₀ values for the inhibition of an MAO isoform. The most potent inhibitor exhibit an IC₅₀ value of 0.011 μM for MAO-A. This study proposes that high potency MAO inhibitors such as those investigated here, may act as lead compounds for the development of treatments for neurodegenerative and neuropsychiatric disorders such as Parkinson's disease and depression.     

Rapid synthesis of flavone‐based monoamine oxidase (MAO) inhibitors targeting two active sites using click chemistry

A new library of flavone derivatives targeting two active sites of monoamine oxidases (“aromatic cage” and substrate cavity) were designed and synthesized using click chemistry (CuAAC reaction) between 6‐N₃‐2‐phenyl chromones ( Az1–Az2 ) and a series of alkynes ( k1–k20 ). Their inhibitory activities against MAO isoforms (MAO‐A and MAO‐B) are evaluated. Compounds with fluorine, amide bonds, or amino bonds have shown better inhibition. The most potent flavone MAO inhibitor studied is Az2k19 (1.6 μm for MAO‐A, 2.1 μm for MAO‐B), while Az1k15 and Az2k15 displayed better selectivity toward MAO‐B (SI > 10). Docking studies are in accordance with our hypothesis that these inhibitors are most likely located at both the substrate cavity and the “aromatic cage”. Our results show that it is considerable to develop new MAO inhibitors from C6 substitution of flavone derivatives and that these compounds are also potential for the treatment of diseases associated with MAOs.     

Novel tetrahydroacridine derivatives with iodobenzoic acid moiety as multifunctional acetylcholinesterase inhibitors

New synthesized series of 9‐amino‐1,2,3,4‐tetrahydroacridine derivatives with iodobenzoic acid moiety were studied for their inhibitory activity toward cholinesterase and against β‐amyloid aggregation. All novel molecules 3a–3i interacted with both cholinesterases—acetylcholinesterase and butyrylcholinesterase—delivered nanomolar IC₅₀ values. The structure–activity relationship showed that N‐butyl moiety derivatives are stronger inhibitors toward AChE and BuChE than N‐ethyl and N‐propyl moieties compounds. The most potent compound toward acetylcholinesterase was inhibitor 3f (IC₅₀ = 31.2 nm ), and it was more active than reference drug, tacrine (IC₅₀ = 100.2 nm ). Compound 3f showed strong inhibition of butyrylcholinesterase (IC₅₀ = 8.0 nm ), also higher than tacrine (IC₅₀ = 16.3 nm ). In the kinetic studies, compound 3f revealed mixed type of acetylcholinesterase inhibition. The computer modeling was carried out. The most active compound 3f was confirmed as peripheral anionic site inhibitor of acetylcholinesterase. Moreover, molecule 3f inhibited β‐amyloid aggregation (at the concentration 10 μm —24.96% of inhibition, 25 μm —72%, 50 μm —78.44%, and 100 μm —84.92%). Therefore, among all examined, compound 3f is the most promising molecule for further, more detailed research of novel multifunctional agents in the therapy of Alzheimer's disease.     

Identification of Novel Selective Lysine‐Specific Demethylase 1 (LSD1) Inhibitors Using a Pharmacophore‐Based Virtual Screening Combined with Docking

Lysine‐specific demethylase 1 (LSD1) plays an important role in regulating the lysine methylation at residues K4 and K9 on histone H3. High levels of LSD1 expression have been observed in several malignant tumors. In this study, we presented a pharmacophore‐based virtual screening of a moderate database of 171 143 small molecules. A pharmacophore of LSD1 inhibitors was constructed for the first time and then used to screen the compound library combined with validated molecular docking tools followed by biochemical assays, led to the identification of 9 novel LSD1 inhibitors, showing their IC₅₀ values in a range of 2.41–101 μm . Furthermore, compound XZ 09 exhibited less inhibition against the homologous monoamine oxidase A (MAO‐A) and B (MAO‐B) displaying its moderate selectivity. Our study provides an effective virtual screening method to identify new LSD1 inhibitors and XZ09 represents a potent and selective lead compound to deserve further optimization for the treatment of LSD1 overexpressing cancers.     

Evaluation of multifunctional synthetic tetralone derivatives for treatment of Alzheimer's disease

Neurodegeneration, a complex disease state, comprises several pathways that contribute to cell death. Conventional approach of targeting only one of these pathways has not been proven to be entirely successful and has demanded a hypothetical change as to how researchers design and develop new drugs. In this study, effects of a series of α, β‐unsaturated carbonyl‐based tetralone derivatives against Alzheimer's disease (AD) were investigated. Moreover, their activity toward amyloid β‐induced cytotoxicity was also studied. Six compounds including 3f , 3o , 3u , 3ae , 3af , and 3ag were discovered to be most protective against Aβ‐induced neuronal cell death in PC12 cells. The findings of in vitro experiment revealed that most of these compounds exhibited potent inhibitory activity against MAO‐B, AChE, and self‐induced Aβ_1–42 aggregation. The compound 3f exhibited best AChE (IC₅₀ = 0.045 ± 0.02 μm ) inhibitory potential in addition to potent inhibition of MAO‐B (IC₅₀ = 0.88 ± 0.12 μm ). Furthermore, compound 3f disassembled the Aβ fibrils produced by self‐induced Aβ aggregation by 78.2 ± 4.8%. Collectively, these findings suggest that some compounds from this series have potential to be promising multifunctional agents for AD treatment.     

Synthesis and Biological Evaluation of 2,4,6-Trihydroxychalcone Derivatives as Novel Protein Tyrosine Phosphatase 1B Inhibitors

A series of 2,4,6‐trihydroxychalcone derivatives were synthesized and identified as reversible and competitive protein tyrosine phosphatase (PTP) 1B inhibitors with IC₅₀ values in the micromolar range. Compound 4a had the greatest in vitro inhibition activity against PTP1B (IC₅₀ = 0.27 ± 0.01 μm ) and the best selectivity (6.9‐fold) for PTP1B relative to T‐cell protein tyrosine phosphatases. The compounds identified herein provide a foundation on which to design specific inhibitors of PTP1B and other PTPs.     

Design,synthesis, and molecular docking studies of N‐(9,10‐anthraquinone‐2‐carbonyl)amino acid derivatives as xanthine oxidase inhibitors

A series of N‐(9,10‐anthraquinone‐2‐carbonyl)amino acid derivatives ( 1a–j ) was designed and synthesized as novel xanthine oxidase inhibitors. Among them, the L/D‐phenylalanine derivatives ( 1d and 1i ) and the L/D‐tryptophan derivatives ( 1e and 1j ) were effective with micromolar level potency. In particular, the L‐phenylalanine derivative 1d (IC₅₀ = 3.0 μm ) and the D‐phenylalanine derivative 1i (IC₅₀ = 2.9 μm ) presented the highest potency and were both more potent than the positive control allopurinol (IC₅₀ = 8.1 μm ). Preliminary SAR analysis pointed that an aromatic amino acid fragment, for example, phenylalanine or tryptophan, was essential for the inhibition; the D‐amino acid derivative presented equal or greater potency compared to its L‐enantiomer; and the 9,10‐anthraquinone moiety was welcome for the inhibition. Molecular simulations provided rational binding models for compounds 1d and 1i in the xanthine oxidase active pocket. As a result, compounds 1d and 1i could be promising lead compounds for further investigation.     

Synthesis and Biological Evaluation of Heterocyclic Carboxylic Acyl Shikonin Derivatives

A series of shikonin derivatives ( 1 – 13 ) that were acylated selectively by various thiophene or indol carboxylic acids at the side chain of shikonin were synthesized, and their biological activities were also evaluated as potential tubulin inhibitors. Among them, compound 3 ((R)‐1‐(5,8‐dihydroxy‐1,4‐dioxo‐1,4‐dihydronaphthalen‐2‐yl)‐4‐methylpent‐3‐enyl 3‐(1H‐indol‐3‐yl)propanoate) and compound 8 ((R)‐1‐(5,8‐dihydroxy‐1,4‐dioxo‐1,4‐dihydronaphthalen‐2‐yl)‐4‐methylpent‐3‐enyl 2‐(thiophen‐3‐yl)acetate) exhibited good antiproliferative activity of A875 (IC₅₀ = 0.005 ± 0.001 μm , 0.009  ± 0.002 μm ) and HeLa (IC₅₀ = 11.84 ± 0.64 μm , 4.62  ± 0.31 μm ) cancer cell lines in vitro, respectively. Shikonin (IC₅₀ = 0.46 ± 0.002 μm , 4.80 ± 0.48 μm ) and colchicine (IC₅₀ = 0.75 ± 0.05 μm , 17.79 ± 0.76 μm ) were used as references. Meanwhile, they also showed the most potent growth inhibitory activity against tubulin (IC₅₀ of 3.96  ± 0.13 μm and 3.05 ± 0.30 μm , respectively), which were compared with shikonin (IC₅₀ =  15.20 ± 0.25 μm ) and colchicine (IC₅₀ = 3.50 ± 0.35 μm ). Furthermore, from the results of flow cytometer, we found compound 3 can really inhibit HeLa cell proliferation and has low cell toxicity. Based on the preliminary results, compound 3 with potent inhibitory activity in tumor growth may be a potential anticancer agent.     

Synthesis and Biological Evaluation of Fluorinated 3‐Phenylcoumarin‐7‐O‐Sulfamate Derivatives as Steroid Sulfatase Inhibitors

In the present work, we report the initial results of our study on a series of 3‐phenylcoumarin sulfamate‐based compounds containing C‐F bonds as novel inhibitors of steroid sulfatase. The new compounds are potent steroid sulfatase inhibitors, possessing more than 10 times higher inhibitory potency than coumarin‐7‐O‐sulfamate. In the course of our investigation, compounds 2b and 2c demonstrated the highest inhibitory effect on the enzymatic steroid sulfatase assay; both had IC₅₀ values of 0.27 μm (the IC₅₀ value of coumarin‐7‐O‐sulfamate is 3.5 μm , used as a reference).     

Synthesis and Selective Human Monoamine Oxidase B Inhibition of Heterocyclic Hybrids Based on Hydrazine and Thiazole Scaffolds

A new scaffold of hydrazothiazoles has been designed as monoamine oxidase (MAO) inhibitors combining the hydrazine moiety of iproniazid and the thiazole nucleus of glitazones, a class of peroxisome proliferator‐activated receptor (PPAR)γ agonists recently co‐crystallized with human MAO‐B. The resulting derivatives were synthesized and assayed to evaluate their in vitro activity against both the A and B isoforms of hMAO. All compounds were shown to be selective hMAO‐B inhibitors with IC₅₀ values in the low micromolar/high nanomolar range. Such results suggest that the hydrazothiazole scaffold could be considered as an interesting pharmacophore for the future design of new lead compounds as coadjuvants for the treatment of neurodegenerative diseases.     

Synthesis and biological evaluation of novel N‐aryl‐ω‐(benzoazol‐2‐yl)‐sulfanylalkanamides as dual inhibitors of α‐glucosidase and protein tyrosine phosphatase 1B

α‐Glucosidase is known to catalyze the digestion of carbohydrates and release free glucose into the digestive tract. Protein tyrosine phosphatase 1B (PTP1B) is engaged in the dephosphorylation of the insulin receptor and regulation of insulin sensitivity. Therefore, dual antagonists by targeting both α‐glucosidase and PTP1B may be potential candidates for type 2 diabetes therapy. In this work, three series of novel N‐aryl‐ω‐(benzoazol‐2‐yl)‐sulfanylalkanamides were synthesized and assayed for their α‐glucosidase and PTP1B inhibitory activities, respectively. Compound 3l , exhibiting the most effective α‐glucosidase inhibitory activity (IC₅₀ = 10.96 μm ( 3l ), IC₅₀ = 51.32 μm (Acarbose), IC₅₀ = 18.22 μm (Ursolic acid)) and potent PTP1B inhibitory activity (IC₅₀ = 13.46 μm ( 3l ), IC₅₀ = 14.50 μm (Ursolic acid)), was identified as a novel dual inhibitor of α‐glucosidase and PTP1B. Furthermore, 3l is a highly selective PTP1B inhibitor because no inhibition was showed by 3l at 100 μm against PTP‐MEG2, TCPTP, SHP2, or SHP1. Subsequent kinetic analysis revealed 3l inhibited α‐glucosidase in a reversible and mixed manner. Molecular docking study indicated that hydrogen bonds, van der Waals, charge interactions and Pi‐cation interactions all contributed to affinity between 3l and α‐glucosidase/PTP1B.     

Synthesis,Biological Evaluation,and Computer‐Aided Drug Designing of New Derivatives of Hyperactive Suberoylanilide Hydroxamic Acid Histone Deacetylase Inhibitors

The synthesis and biological evaluation of a novel series of compounds based on suberoylanilide hydroxamic acid (SAHA) had been designed as potential histone deacetylase inhibitors (HDACis). Molecular docking studies indicated that our derivatives had better fitting in the binding sites of HDAC8 than SAHA. Compounds 1–5 were synthesized through the synthetic routes. In biological test, compounds also showed good inhibitory activity in HDAC enzyme assay and more potent growth inhibition in human glioma cell lines (MGR2, U251, and U373). A representative compound, N3F, exhibited better inhibitory effect (HDAC, IC₅₀ = 0.1187 μm ; U251, IC₅₀ = 0.8949 μm ) and lower toxicity for human normal cells (LO2, IC₅₀ = 172.5 μm and MRC5, IC₅₀ = 213.6 μm ) compared with SAHA (HDAC, IC₅₀ = 0.8717 μm ; U251, IC₅₀ = 8.938 μm ; LO2, IC₅₀ = 86.52 μm and MRC5, IC₅₀ = 81.02 μm ). In addition, N3F obviously increased Beclin‐1 and Caspase‐3 and 9 as well as inhibited Bcl‐2 in U251 cells. All of our results indicated that these SAHA cap derivatives could serve as potential lead compounds for further optimization. In addition, N3F and N2E both displayed promising profile as antitumor candidates for the treatment of human glioma.     

Design and synthesis of 4′‐((5‐benzylidene‐2,4‐dioxothiazolidin‐3‐yl)methyl)biphenyl‐2‐carbonitrile analogs as bacterial peptide deformylase inhibitors

Herein, we report the synthesis and screening of 4′‐((5‐benzylidene‐2,4‐dioxothiazolidin‐3‐yl)methyl)biphenyl‐2‐carbonitrile analogs 11(a–j) as bacterial peptide deformylase (PDF) enzyme inhibitors. The compounds 11b (IC₅₀ value = 139.28 μm ), 11g (IC₅₀ value = 136.18 μm ), and 11h (IC₅₀ value = 131.65 μm ) had shown good PDF inhibition activity. The compounds 11b (MIC range = 103.36–167.26 μg/mL), 11g (MIC range = 93.75–145.67 μg/mL), and 11h (MIC range = 63.61–126.63 μg/mL) had also shown potent antibacterial activity when compared with standard ampicillin (MIC range = 100.00–250.00 μg/mL). Thus, the active derivatives were not only PDF inhibitors but also efficient antibacterial agents. To gain more insight on the binding mode of the compounds with PDF enzyme, the synthesized compounds 11(a–j) were docked against PDF enzyme of Escherichia coli and compounds exhibited good binding properties. The results suggest that this class of compounds has potential for development and use in future as antibacterial drugs.     

Inhibitory effects of sulfonylureas and non‐steroidal anti‐inflammatory drugs on in vitro metabolism of canagliflozin in human liver microsomes

Canagliflozin, used to treat type 2 diabetes mellitus (T2DM), is commonly co‐administered with sulfonylureas. The objective of the present study was to evaluate the possible inhibitory effect of sulfonylureas and non‐steroidal anti‐inflammatory drugs (NSAIDs) on canagliflozin metabolism in vitro. Three sulfonylurea derivatives were evaluated as inhibitors: chlorpropamide, glimepiride and gliclazide. Two other NSAIDs were used as positive control inhibitors: niflumic acid and diclofenac. The rate of formation of canagliflozin metabolites was determined by HPLC analysis of in vitro incubations of canagliflozin as a substrate with and without inhibitors, using human liver microsomes (HLMs). Among sulfonylureas, glimepiride showed the most potent inhibitory effect against canagliflozin M7 metabolite formation, with an IC₅₀ value of 88 μm , compared to chlorpropamide and gliclazide with IC₅₀ values of more than 500 μm . Diclofenac inhibited M5 metabolite formation more than M7, with IC₅₀ values of 32 μm for M5 and 80 μm for M7. Niflumic acid showed no inhibition activity against M5 formation, but had relatively selective inhibitory potency against M7 formation, which is catalysed by UGT1A9, with an IC₅₀ value of 1.9 μm and an inhibition constant value of 0.8 μm . A clinical pharmacokinetic interaction between canagliflozin and sulfonylureas is unlikely. However, a possible clinically important drug interaction between niflumic acid and canagliflozin has been identified.