Synthesis of a novel series of non-symmetrical bispyridinium compounds bearing a xylene linker and evaluation of their reactivation activity against tabun and paraoxon-inhibited acetylcholinesterase

Nine potential non-symmetrical xylene-bridged AChE reactivators were synthesized using modifications of currently known synthetic pathways. Their potency to reactivate AChE inhibited by the nerve agent tabun and the insecticide paraoxon together with nine symmetrical xylene-bridged compounds, was tested in vitro. Seven compounds were promising against paraoxon-inhibited AChE. Two compounds were found to be more potent against tabun-inhibited AChE than obidoxime at a concentration applicable in vivo.     

Novel series of bispyridinium compounds bearing a (Z)-but-2-ene linker--synthesis and evaluation of their reactivation activity against tabun and paraoxon-inhibited acetylcholinesterase

Six novel AChE reactivators with a (Z)-but-2-ene linker were synthesized using the known synthetic pathways. Their ability to reactivate AChE, which had been previously inhibited by nerve agent tabun or pesticide paraoxon, was tested in vitro and compared to pralidoxime, HI-6, obidoxime, and K075. The novel synthesized compounds were found to be ineffective against GA-inhibited AChE but the ability of (Z)-1,4-bis(4-hydroxyiminomethylpyridinium)-but-2-ene dibromide to reactivate paraoxon-inhibited AChE was comparable with that of oxime K075. Notably, the oxime group in position four substantially increased the ability of the novel compounds to reactivate paraoxon-inhibited AChE.     

Discovery of isoalloxazine derivatives as a new class of potential anti-Alzheimer agents and their synthesis

This article describes discovery of a novel and new class of cholinesterase inhibitors as potential therapeutics for Alzheimer’s disease. A series of novel isoalloxazine derivatives were synthesized and biologically evaluated for their potential inhibitory outcome for both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). These compounds exhibited high activity against both the enzymes AChE as well as BuChE. Of the synthesized compounds, the most potent isoalloxazine derivatives (7m and 7q) showed IC₅₀ values of 4.72 μM and 5.22 μM respectively against AChE; and, 6.98 μM and 5.29 μM respectively against BuChE. These two compounds were further evaluated for their anti-aggregatory activity for β-amyloid (Aβ) in presence and absence of AChE by performing Thioflavin-T (ThT) assay and Congo red (CR) binding assay. In order to evaluate cytotoxic profile of these two potential compounds, cell viability assay of SH-SY5Y human neuroblastoma cells was performed. Further, to understand the binding behavior of these two compounds with AChE and BuChE enzymes, docking studies have been reported.     

Synthesis and molecular docking studies of some 4-phthalimidobenzenesulfonamide derivatives as acetylcholinesterase and butyrylcholinesterase inhibitors

A series of 4-phthalimidobenzenesulfonamide derivatives were designed, synthesized and evaluated for the inhibitory activities against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). Structures of the title compounds were confirmed by spectral and elemental analyses. The cholinesterase (ChE) inhibitory activity studies were carried out using Ellman’s colorimetric method. The biological activity results revealed that all of the title compounds (except for compound 8) displayed high selectivity against AChE. Among the tested compounds, compound 7 was found to be the most potent against AChE (IC₅₀=?1.35?±?0.08?μM), while compound 3 exhibited the highest inhibition against BuChE (IC₅₀=?13.41?±?0.62?μM). Molecular docking studies of the most active compound 7 in AChE showed that this compound can interact with both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE.     

Choline derivatives and sodium fluoride protect acetylcholinesterase against irreversible inhibition and aging by DFP and paraoxon

A light addressable potentiometric sensor was used to measure acetylcholinesterase (AChE) activity in order to evaluate the protective effects of quaternary compounds and NaF against enzyme phosphorylation and aging by two organophosphates. The use of the immobilized AChE made possible the quick removal of reagents (i.e., organophosphate, 2-pralidoxime, and protectant), thereby permitting accurate determination of AChE activity before and after phosphorylation and aging. Paraoxon was 15-fold more potent in inhibiting AChE than DFP, while the percent aging following phosphorylation by diiso-propylfluorophosphate (DFP) was much higher. Sodium fluoride (NaF), the most effective protectant against phosphorylation and aging, and the quaternary ammonium compounds reduced significantly AChE inhibition by DFP and paraoxon, to similar degrees. Even though the percent AChE activity that was lost to aging was reduced by these agents, aging as a percent of phosphorylated AChE was not reduced. Thus, their major effect was in reducing the percent AChE phosphorylation, which consequently resulted in reduction of total aged AChE. The finding that quaternary ammonium compounds protect against phosphorylation is consonant with the proposed presence of the active site of AChE in an aromatic gorge.     

Synthesis,biological activity and molecular modeling studies on 1H-benzimidazole derivatives as acetylcholinesterase inhibitors

A series of N-{2-[4-(1H-benzimidazole-2-yl)phenoxy]ethyl}substituted amine derivatives were designed to assess cholinesterase inhibitor activities. Acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitor activities were evaluated in vitro by using Ellman’s method. It was discovered that most of the compounds displayed AChE and/or BuChE inhibitor activity and few compounds were selective against AChE/BuChE. Compound 3c and 3e were the most active compounds in the series against eeAChE and hAChE, respectively. Molecular docking studies and molecular dynamics simulations were also carried out.     

2-Phenoxy-indan-1-one derivatives as acetylcholinesterase inhibitors: a study on the importance of modifications at the side chain on the activity

As a part of our project aimed at developing new agents of potential application in AD, a new series of 2-phenoxy-indan-1-one derivatives which possess alkylamine side chain were designed, synthesized, and evaluated for their inhibitory activity against AChE and BuChE. Most of the compounds were found to inhibit AChE in the nanomolar range. The optimum inhibitor 3g exhibited 34-fold increase in AChE inhibition than donepezil and displayed neuroprotective effect against H(2)O(2)-induced cell death.     

The preparation, in vitro screening and molecular docking of symmetrical bisquaternary cholinesterase inhibitors containing a but-(2E)-en-1,4-diyl connecting linkage

Carbamate inhibitors (e.g. pyridostigmine bromide) are used as a pre-treatment for the prevention of organophosphorus poisoning. They work by blocking the native function of acetylcholinesterases (AChE) and thus protect AChE against irreversible inhibition by organophosphorus compounds. However, carbamate inhibitors are known for their many undesirable side effects related to the carbamylation of AChE. In this paper, we describe 17 novel bisquaternary compounds and have analysed their effect on AChE inhibition. The newly prepared compounds were evaluated in vitro using both human erythrocyte AChE and human plasmatic butyrylcholinesterase. Their inhibitory ability was expressed as the half maximal inhibitory concentration (IC??) and then compared to the standard carbamate drugs and two AChE reactivators. One of these novel compounds showed promising AChE inhibition in vitro (nM range) and was better than the currently used standards. Additionally, a kinetic assay confirmed the non-competitive inhibition of hAChE by this novel compound. Consequently, the docking results confirmed the apparent π-π or π-cationic interactions with the key amino acid residues of hAChE and the binding of the chosen compound at the enzyme catalytic site.     

The preparation,in vitro screening and molecular docking of symmetrical bisquaternary cholinesterase inhibitors containing a but-(2E)-en-1,4-diyl connecting linkage

Carbamate inhibitors (e.g. pyridostigmine bromide) are used as a pre-treatment for the prevention of organophosphorus poisoning. They work by blocking the native function of acetylcholinesterases (AChE) and thus protect AChE against irreversible inhibition by organophosphorus compounds. However, carbamate inhibitors are known for their many undesirable side effects related to the carbamylation of AChE. In this paper, we describe 17 novel bisquaternary compounds and have analysed their effect on AChE inhibition. The newly prepared compounds were evaluated in vitro using both human erythrocyte AChE and human plasmatic butyrylcholinesterase. Their inhibitory ability was expressed as the half maximal inhibitory concentration (IC₅₀) and then compared to the standard carbamate drugs and two AChE reactivators. One of these novel compounds showed promising AChE inhibition in vitro (nM range) and was better than the currently used standards. Additionally, a kinetic assay confirmed the non-competitive inhibition of hAChE by this novel compound. Consequently, the docking results confirmed the apparent π-π or π-cationic interactions with the key amino acid residues of hAChE and the binding of the chosen compound at the enzyme catalytic site.     

Protection from quinidine or physostigmine against in vitro inhibition by sarin of acetylcholinesterase activity

We have studied the relative effectiveness of quinidine and physostigmine in protecting against the inhibition of acetylcholinesterase (AChE) by sarin, an organophosphate (OP) compound. The protective effects of these compounds were studied in vitro in both synaptosomal and soluble samples obtained from various regions of sarin-administered or control isolated, perfused canine brain. Although AChE activities in the sarin-administered brain were substantially lower than in the control brain, we observed regional differences in the AChE activity in both. The AChE in the control brain and the AChE remaining in sarin-administered brain had different susceptibilities to inhibition from OP compounds in vitro and, therefore, have different properties. Quinidine partially protected AChE from the inhibitory effects of sarin in vitro possibly by altering the sarin binding sites. Addition of sarin to physostigmine-treated control brain samples allowed partial recovery of the AChE activity. The protective effects of quinidine or physostigmine were lost when samples from sarin-administered brain were treated in vitro with these compounds and then again exposed to sarin. Therefore, both quinidine and physostigmine provided partial protection against the inhibitory effects of sarin in vitro if they were added prior to sarin.     

Synthesis and screening for acetylcholinesterase inhibitor activity of some novel 2-butyl-1,3-diaza-spiro[4,4]non-1-en-4-ones: derivatives of irbesartan key intermediate

The association of bioactive nucleus with other pharmacological agents is hoped to improve the efficacy of the treatment by combining the effects of different pharmacological mechanisms of action. Keeping this in view, a series of 2-butyl-1,3-diaza-spiro[4,4]non-1-en-4-one derivatives have been synthesized by interaction of 2-butyl-1,3-diaza-spiro[4,4]non-1-en-4-one with different bioactive aralkyl halides in presence of powdered potassium carbonate by two different methods viz., conventional and microwave irradiation. The yields under conventional and microwave irradiation methods were in the range of 60-65% and 80-90%, respectively. The structure elucidation of the new compounds has been carried out with the help of elemental analysis and spectral data. All the synthesized compounds have been screened for their efficacy as acetylcholinesterase (AChE) inhibitor. AChE inhibitory activity study was carried out by using Ellman colorimetric assay with neostigmine as a reference standard against targets from different species, such as pure electric eel AChE, human serum AChE, and rat brain AChE. Among the compounds synthesized, compounds 5a, 5b, 5j showed good inhibition against AChE.     

Synthesis,structure–activity relationship and molecular docking of 3-oxoaurones and 3-thioaurones as acetylcholinesterase and butyrylcholinesterase inhibitors

The present study describes efficient and facile syntheses of varyingly substituted 3-thioaurones from the corresponding 3-oxoaurones using Lawesson’s reagent and phosphorous pentasulfide. In comparison, the latter methodology was proved more convenient, giving higher yields and required short and simple methodology. The structures of synthetic compounds were unambiguously elucidated by IR, MS and NMR spectroscopy. All synthetic compounds were screened for their inhibitory potential against in vitro acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes. Molecular docking studies were also performed in order to examine their binding interactions with AChE and BChE human proteins. Both studies revealed that some of these compounds were found to be good inhibitors against AChE and BChE.     

Design,Synthesis, Molecular Docking,and Cholinesterase Inhibitory Potential of Phthalimide‐Dithiocarbamate Hybrids as New Agents for Treatment of Alzheimer's Disease

A novel series of phthalimide‐dithiocarbamate hybrids was synthesized and evaluated for in vitro inhibitory potentials against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). The anti‐cholinesterase results indicated that among the synthesized compounds, the compounds 7g and 7h showed the most potent anti‐AChE and anti‐BuChE activities, respectively. Molecular docking and dynamic studies of the compounds 7g and 7h , respectively, in the active site of AChE and BuChE revealed that these compounds as well interacted with studied cholinesterases. These compounds also possessed drug‐like properties and were able to cross the BBB.     

Synthesis of asymmetrical bispyridinium compounds bearing cyano-moiety and evaluation of their reactivation activity against tabun and paraoxon-inhibited acetylcholinesterase

Three asymmetrical AChE reactivators with cyano-moiety and propane linker were synthesized using modification of currently known synthetic pathways. Their potency to reactivate AChE inhibited by nerve agent tabun and insecticide paraoxon was tested in vitro and compared to pralidoxime, HI-6, obidoxime, K027, and K048. According to the results, three compounds seem to be promising against paraoxon-inhibited AChE. Better results were obtained for bisquaternary substances at least with one oxime group in position four. None of tested substances was able to satisfactorily reactivate tabun-inhibited AChE at concentration applicable for in vivo experiments.     

Design,synthesis, and biological evaluation of novel 4-oxobenzo[d]1,2,3-triazin-benzylpyridinum derivatives as potent anti-Alzheimer agents

Novel 4-oxobenzo[d]1,2,3-triazin derivatives bearing pyridinium moiety 6a–q were synthesized and screened against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). Most of the synthesized compounds showed good inhibitory activity against AChE. Among the synthesized compounds, the compound 6j exhibited the highest AChE inhibitory activity. It should be noted that these compounds displayed low anti-BuChE activity with the exception of the compound 6i, as it exhibited BuChE inhibitory activity more than donepezil. The kinetic study of the compound 6j revealed that this compound inhibited AChE in a mixed-type inhibition mode. This finding was also confirmed by the docking study. The latter study demonstrated that the compound 6j interacted with both the catalytic site and peripheral anionic site of the AChE active site. The compound 6j was also observed to have significant neuroprotective activity against H₂O₂-induced PC12 oxidative stress, but low activity against β-secretase.     

Intermolecular amination of allylic and benzylic alcohols leads to effective inhibitions of acetylcholinesterase enzyme and carbonic anhydrase I and II isoenzymes

In this study, we aimed to determine the inhibition effects of novel synthesized sulfamates ( 2a–g ), sulfonamides ( 3b–f ), carbonyl sulfonamides ( 3h and i ), and carbonyl sulfamates ( 4h and 4i ), which were tested against two human cytosolic carbonic anhydrase I and II isozymes (hCA I and II) and acetylcholinesterase (AChE) enzyme. For inhibition properties of allylic sulfamates, the half maximal inhibitory concentration (IC₅₀) and inhibition constant (K_i) were calculated for each novel compounds. The allylic sulfamates showed that K_i values are in the range of 187.33–510.31 pM for hCA I, 104.22–290.09 pM against hCA II, and 12.73–103.63 pM against AChE. The results demonstrated that all newly synthesized compounds had shown effective inhibition against hCA I and II isoenzymes and AChE enzyme.     

Biochemical evaluation and molecular docking assessment of Cymbopogon citratus as a natural source of acetylcholine esterase (AChE)- targeting insecticides

Acetylcholinesterase (AChE) has been an effective target for insecticide development which is a very important aspect of the global fight against insect-borne diseases. The drastic reduction in the sensitivity of insects to AChE-targeting insecticides like organophosphates and carbamates have increased the need for insecticides of natural origin. In this study, we used Drosophila melanogaster as a model to investigate the insecticidal and AChE inhibitory potentials of Cymbopogon citratus and its bioactive compounds. Flies were exposed to 100 and 200 mg/mL C. citratus leaf extract for a 3-h survival assay followed by 45 min exposure for negative geotaxis and biochemical assays. Molecular docking analysis of 45 bioactive compounds of the plant was conducted against Drosophila melanogaster AChE (DmAChE). Exposure to C. citratus significantly reduced the survival rate of flies throughout the exposure period and this was accompanied by a significant decrease in percentage negative geotaxis, AChE activity, catalase activity, total thiol level and a significant increase in glutathione-S-transferase (GST) activity. The bioactive compounds of C. citratus showed varying levels of binding affinities for the enzyme. (+)-Cymbodiacetal scored highest (?9.407 kcal/mol) followed by proximadiol (?8.253 kcal/mol), geranylacetone (?8.177 kcal/mol), and rutin (?8.148 kcal/mol). The four compounds occupied the same binding pocket and interacted with important active site amino acid residues as the co-crystallized ligand (1qon). These compounds could be responsible for the insecticidal and AChE inhibitory potentials of C. citratus and they could be further explored in the development of AChE-targeting insecticides.     

Design,Synthesis, and Biological Evaluation of Novel Indanone Derivatives as Cholinesterase Inhibitors for Potential Use in Alzheimer's Disease

Indanone derivatives containing meta/para-substituted aminopropoxy benzyl/benzylidene moieties were designed based on the structures of donepezil and ebselen analogs as the cholinesterase inhibitors. The designed compounds were synthesized and their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities were measured. Inhibitory potencies (IC₅₀ values) for the synthesized compounds ranged from 0.12 to 11.92 μM and 0.04 to 24.36 μM against AChE and BChE, respectively. Compound 5 c showed the highest AChE inhibitory potency with IC₅₀ value of 0.12 μM, whereas the highest BChE inhibition was achieved by structure 7 b (IC₅₀=0.04 μM). Structure-activity relationship (SAR) analysis revealed that there is no significant difference between meta and para-substituted derivatives in AChE and BChE inhibition. However, the most potent AChE inhibitor 5 c belongs to meta-substituted compounds, while the most active BChE inhibitor is para-substituted derivative 7 b . The order of enzyme inhibition potency based on the substituted amine group is dimethyl amine>piperidine>morpholine. Compounds containing C=C linkage are more potent AChE inhibitors than the corresponding saturated structures. Molecular docking studies indicated that 5 c interacts with AChE in a very similar way to that observed experimentally for donepezil. The introduced indanone-aminopropoxy benzylidenes could be used in drug-discovery against Alzheimer's disease.     

Preparation, in vitro screening and molecular modelling of symmetrical 4-tert-butylpyridinium cholinesterase inhibitors--analogues of SAD-128

Carbamate inhibitors (e.g., pyridostimine bromide) are used as a pre-exposure treatment for the prevention of organophosphorus poisoning. They work by blocking acetylcholinesterase’s (AChE) native function and thus protect AChE against irreversible inhibition by organophosphorus compounds. However, carbamate inhibitors are known for many undesirable side-effects related to the carbamylation of AChE. In this Letter, 19 analogues of SAD-128 were prepared and evaluated as cholinesterase inhibitors. The screening results showed promising inhibitory ability of four compounds better to used standards (pralidoxime, obidoxime, BW284c51, ethopropazine, SAD-128). Four most promising compounds were selected for further molecular docking studies. The SAR was stated from obtained data. The former receptor studies were reported and discussed. The further in vivo studies were recommended in the view of OP pre-exposure treatment.     

Design,synthesis and evaluation of a novel metal chelator as multifunctional agents for the treatment of Alzheimer’s disease

A series of compounds following the lead compounds including deferasirox and tacrine were designed, synthesized and evaluated as multifunctional agents against Alzheimer’s disease (AD). In vitro studies showed that most synthesized compounds exhibited good multifunctional activities in inhibiting acetylcholinesterase (bAChE), and chelating metal ions. Especially, compound TD_e demonstrated significant metal chelating property, a moderate acetylcholinesterase (AChE) inhibitory activity and an antioxidant activity. Results from the molecular modeling indicated that TD compounds were mixed-type inhibitor, binding simultaneously to the catalytic anionic site (CAS) and the peripheral anionic site (PAS) of TcAChE. Moreover, TD_e showed a low cytotoxicity but a good protective activity against the injury caused by H₂O₂. These results suggest that TD compounds might be considered as attractive multi-target cholinesterase inhibitor and will play important roles in the treatment of AD.