Synthesis and biological evaluation of thiophene derivatives as acetylcholinesterase inhibitors

A series of new thiophene derivatives has been synthesized using the Gewald protocol. The acetylcholinesterase inhibition activity was assayed according to Ellman's method using donepezil as reference. Some of the compounds were found to be more potent inhibitors than the reference. 2-(2-(4-(4-Methoxyphenyl)piperazin-1-yl)acetamido)-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxamide (IIId) showed 60% inhibition, compared to only 40% inhibition by donepezil.     

Molecular Docking and Design of Novel Heterodimers of Donepezil and Huperzine Fragments as Acetylcholinesterase Inhibitors

To provide hints for the design of new acetylcholinesterase(ACh E) inhibitors with higher potency and specificity, the binding modes of novel heterodimers comprised of donepezil and huperzine A fragments with ACh E were explored by employing the docking simulations. The results show that the binding mode of S-17b(the most potent inhibitor in Ref. 2, i.e., Bioorg. Med. Chem. 2013, 21, 676-683) is clearly different from that of donepezil, while the binding modes of other heterodimers in Ref. 2 are the same as that of donepezil. In addition, based on the binding mode and structure modification of S-17 b, two novel inhibitors(S-17b1 and S-17bb1) with much higher inhibitory potency than S-17 b were obtained. Our design strategy was to replace the hupyridone moiety of S-17 b with the bulky group, and to replace the dimethoxyindanone moiety of S-17 b with more hydrophobic and bulky group with a highly positive charge, which would result in generating potent and selective AChE inhibitors.     

Synthesis,Biological Evaluation,and In Silico Studies of New Acetylcholinesterase Inhibitors Based on Quinoxaline Scaffold

A quinoxaline scaffold exhibits various bioactivities in pharmacotherapeutic interests. In this research, twelve quinoxaline derivatives were synthesized and evaluated as new acetylcholinesterase inhibitors. We found all compounds showed potent inhibitory activity against acetylcholinesterase (AChE) with IC₅₀ values of 0.077 to 50.080 µM, along with promising predicted drug-likeness and blood–brain barrier (BBB) permeation. In addition, potent butyrylcholinesterase (BChE) inhibitory activity with IC₅₀ values of 14.91 to 60.95 µM was observed in some compounds. Enzyme kinetic study revealed the most potent compound (6c) as a mixed-type AChE inhibitor. No cytotoxicity from the quinoxaline derivatives was noticed in the human neuroblastoma cell line (SHSY5Y). In silico study suggested the compounds preferred the peripheral anionic site (PAS) to the catalytic anionic site (CAS), which was different from AChE inhibitors (tacrine and galanthamine). We had proposed the molecular design guided for quinoxaline derivatives targeting the PAS site. Therefore, the quinoxaline derivatives could offer the lead for the newly developed candidate as potential acetylcholinesterase inhibitors.     

Study of donepezil binding to serum albumin by capillary electrophoresis and circular dichroism

The interaction between human serum albumin (HSA) and the acetylcholinesterase inhibitor donepezil, has been studied by means of capillary electrophoresis frontal analysis (CE/FA) and circular dichroism. CE/FA enabled rapid and direct estimation of the quantity of free donepezil present at equilibrium with a physiological level of serum albumin (600 mol L^–1). Application of Scatchard analysis enabled estimation of the binding parameters of HSA towards donepezil, such as association constant and number of binding sites on one protein molecule. Furthermore, due to enantioseparation ability shown by HSA on donepezil in CE mode, displacement experiments were carried out using ketoprofen and warfarin as coadditives to the HSA based running buffer. The addition of these compounds reduced the enantioresolution of donepezil by HSA only when used at high concentration. These data were confirmed and corroborated by circular dichroism (CD) experiments. Using CD, bilirubin was also applied as a ligand specific to site III of HSA. The observed behaviour suggested that donepezil could be considered a ligand with independent binding to sites I and II; although site III is not the highest affinity site, indirect interaction (i.e. cooperative binding) can be assumed.     

Synthesis and in vitro study of new coumarin derivatives linked to nicotinonitrile moieties as potential acetylcholinesterase inhibitors

The appropriate pyridine-2(1H)-thiones were reacted with an equivalent amount of 5-(chloromethyl)-2-hydroxybenzaldehyde in ethanol in the presence of potassium hydroxide to give the corresponding 2-hydroxybenzaldehyde derivatives in excellent yields. The latter derivatives were taken as key synthons for the preparation of the target hybrids. Therefore, 2-hydroxybenzaldehydes were reacted with benzoylglycine in acetic anhydride in the presence of fused sodium acetate at 100°C for 6 hours to afford a new series of nicotinonitrile-coumarin hybrids. The in vitro acetylcholinesterase inhibitory activities were estimated for the new coumarins. The results were expressed as the inhibition percentage of the tested hybrids at concentration of 25 nM, compared to donepezil as a reference (inhibition percentage of 70.5). Coumarin hybrids linked to 6-(4-nitrophenyl) or 6-(4-chlorophenyl)-4-phenylnicotinonitrile exhibited more effective inhibitory activities than donepezil with inhibition percentages of 94.1 and 72.3, respectively. The new coumarins were tested for their free radical-scavenging capabilities against DPPH. Furthermore, some new coumarins were tested for in vitro cytotoxic activity against each MCF-10A, MCF-7, Caco2, and HEPG2. The new hybrids showed cytotoxicity in micromolar range (IC₅₀ of 3.5-13.9 μM) against all tested cell lines. These results clearly demonstrated that the hybrids being tested are not cytotoxic at the concentration required to inhibit acetylcholinesterase effectively.     

Acetylcholinesterase and butyrylcholinesterase inhibitory compounds from Corydalis cava (Fumariaceae)

Tubers of Corydalis cava were extracted with ethanol and fractionated using n-hexane, chloroform and ethanol. Repeated column chromatography, preparative TLC and crystallization led to the isolation of fifteen isoquinoline alkaloids. The chemical structures of the isolated compounds were determined on the basis of spectroscopic techniques and by comparison with literature data. All isolated compounds were tested for human blood acetylcholinesterase (HuAChE) and human plasma butyrylcholinesterase (HuBuChE) inhibitory activity. (+)-Canadaline inhibited acetylcholinesterase as well as butyrylcholinesterase in a dose-dependent manner with IC50 values of 20.1 +/- 1.1 microM and 85.2 +/- 3.2 microM, respectively. (+)-Canadine, with an IC50 value of 12.4 +/- 0.9 microM, was the most potent inhibitor of acetylcholinesterase, whilst (+/-)-corycavidine and (+)-bulbocapnine were effective inhibitors of butyrylcholinesterase with IC50 values of 46.2 +/- 2.4 microM and 67.0 +/- 2.1 microM, respectively. The other isolated alkaloids were considered inactive (IC50 > 100 microM).     

Sensitive analysis of donepezil in plasma by capillary electrophoresis combining on-column field-amplified sample stacking and its application in Alzheimer's disease

Field-amplified sample stacking (FASS) in capillary electrophoresis (CE) was used to determine the concentration of donepezil, an acetylcholinesterase inhibitor, in human plasma. A sample pretreatment by liquid-liquid extraction with isopropanol/n-hexane (v/v 3:97) and subsequent quantification by FASS-CE was used. Before sample loading, a water plug (0.5 psi, 6 s) was injected to permit FASS. Electrokinetic injection (7 kV, 90 s) was used to introduce sample cations. The separation condition for donepezil was performed in electrolyte solutions containing Tris buffer (60 mM, pH 4.0) with sodium octanesulfonate 40 mM and 0.01% polyvinyl alcohol as a dynamic coating to reduce analytes' interaction with capillary wall. The separation was performed at 28 kV and detected at 200 nm. Using atenolol as an internal standard, the linear ranges of the method for the determination of donepezil in human plasma were over a range of 1-50 ng/mL. The limit of detection was 0.1 ng/mL (S/N=3, sampling 90 s at 7 kV). One female volunteer (54 years old) was orally administered a single dose of 10 mg donepezil (Aricept, Eisai), and blood samples were drawn over a 60 h period for pharmacokinetic study. The method was also applied successfully to monitor donepezil in sixteen Alzheimer's disease patients' plasmas.     

Structure-based 3D QSAR and design of novel acetylcholinesterase inhibitors

The paper describes the construction, validation and application of a structure-based 3D QSAR model of novel acetylcholinesterase (AChE) inhibitors. Initial use was made of four X-ray structures of AChE complexed with small, non-specific inhibitors to create a model of the binding of recently developed aminopyridazine derivatives. Combined automated and manual docking methods were applied to dock the co-crystallized inhibitors into the binding pocket. Validation of the modelling process was achieved by comparing the predicted enzyme-bound conformation with the known conformation in the X-ray structure. The successful prediction of the binding conformation of the known inhibitors gave confidence that we could use our model to evaluate the binding conformation of the aminopyridazine compounds. The alignment of 42 aminopyridazine compounds derived by the docking procedure was taken as the basis for a 3D QSAR analysis applying the GRID/GOLPE method. A model of high quality was obtained using the GRID water probe, as confirmed by the cross-validation method (q² _LOO=0.937, q² _{L50% O}=0.910). The validated model, together with the information obtained from the calculated AChE-inhibitor complexes, were considered for the design of novel compounds. Seven designed inhibitors which were synthesized and tested were shown to be highly active. After performing our modelling study the X-ray structure of AChE complexed with donepezil, an inhibitor structurally related to the developed aminopyirdazines, has been made available. The good agreement found between the predicted binding conformation of the aminopyridazines and the one observed for donepezil in the crystal structure further supports our developed model.     

Design and synthesis of 2,4-dioxochroman-pyridinium-phenylacetamide derivatives as new anti-Alzheimer agents: in vitro and in silico studies

2,4-Dioxochroman-pyridinium-phenylacetamide derivatives 7a–n were synthesized and evaluated for their in vitro cholinesterase (ChE) inhibitory activities against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). Obtained results demonstrated that, among the synthesized compounds, two compounds, 7j and 7k , were more potent than the standard drug donepezil against BuChE and did not show cytotoxicity and carcinogenicity. Furthermore, through molecular modeling and molecular dynamic studies. we showed that these compounds can be located deep in the gorge cavity of BuChE and that they interacted with catalytic residues, acyl, and cholin-binding pockets of this enzyme. Support information     

Identification of novel alpha-glucosidase inhibitors by screening libraries based on N- [4-(benzyloxy) benzoyl] alanine derivatives

A library of 72 compounds related to N- [4-(benzyloxy) benzoyl]alanine (I) was synthesized, prepared and screened for alpha-glucosidase inhibitory activity. Four compounds showed potent inhibition, six compounds moderate inhibition, and 16 were weak inhibitors. One compound, N- [4-(benzyloxy) benzoyl] serine, was found to be a potent inhibitor of alpha-glucosidase with 100% inhibition at 1 micro M. This inhibitor was at least five times more potent than the lead compound I.     

Central cholinergic agents. I. Potent acetylcholinesterase inhibitors, 2-[omega-[N-alkyl-N-(omega-phenyl-alkyl)amino]alkyl]-1H-isoindole- 1,3(2H)-diones, based on a new hypothesis of the enzyme's active site.

It has been suggested that the active site of acetylcholinesterase contains a hydrophobic binding site (HBS-1), which is closely adjacent to both the anionic and the esteratic sites. In this paper, we assumed that there exists another hydrophobic binding site (HBS-2), some distance removed from the anionic site. On this assumption, a new working hypothesis was proposed for the design of acetylcholinesterase inhibitors. A series of 2-[omega-[N-alkyl-N-(omega-phenyl-alkyl)amino]alkyl]-1H- isoindole-1,3(2H)-diones was designed based on this hypothesis and tested for its inhibitory activities on acetylcholinesterase. Some in this series were revealed to be more potent than physostigmine. Optimum activity was found to be associated with a five carbon chain length separating the benzylamino group from the 1H-isoindole-1,3(2H)-dione (phthalimide) moiety. Quantitative study of substitution effect on the phthalimide moiety revealed that hydrophilic and electron-withdrawing groups enhance the activity.     

Synthesis of New Flavanone Derivatives of Farrerol and Preliminary SAR Studies on Anti-VSMCs Vegetation Activity

A series of new flavanone derivatives of farrerol was designed and synthesized as a potent inhibitor of vascular smooth muscle cells(VSMCs) vegetation according to a convenient method. The structures of all the synthesized compounds were confirmed by 1H NMR, 13C NMR and EIHR-MS. The biological activities of these compounds against VSMCs in vitro were evaluated. The assay results indicate that two compounds, 5,7-dihydroxy-6,8-dimethyl- 2-(2-nitrophenyl)chroman-4-one(7f) and 2,3-dibromo-4,5-dihydroxydiphenylm...     

Molecular modelling and enzymatic studies of acetylcholinesterase and butyrylcholinesterase recognition with paraquat and related compounds

The potent herbicide paraquat and three other analogues MPP+, MPDP+ and MPTP have a known toxicological profile linked to the ability to damage dopaminergic neurons. Other biological effects were recently addressed to this class of compounds, including the ability to interact with enzymatic targets involved in the Central Nervous System, such as the acetylcholinesterase (AChE) and the butyrylcholinesterase (BuChE). A combined molecular modelling and enzymatic study focusing onto their interaction against the AChE and BuChE is reported. The former study was performed by docking techniques using target known co-crystallographic models. The latter study was carried out by the widely adopted Ellman's method. In both studies the anti-Alzheimer FDA approved drug tacrine was used as reference inhibitor. Our results indicate that paraquat, MPTP, MPDP+ and MPP+ recognize both enzymatic cleft in a similar fashion compared to the reference inhibitor. A structure-activity correlation was found with the net charge of the ligands, indicating a major role of the electrostatic term in the recognition and inhibition of these compounds. Our data completed their enzymatic profile, added new information on the molecular mechanisms underlying their neurotoxicity useful for the rational design of new cholinesterase inhibitors.     

Synthesis and biological evaluation of benzimidazolone bridged triheterocyclic compounds

A new series of benzimidazolone bridged triheterocyclic compounds bearing thiosemicarbazide, thiadiazole, triazole, moieties was synthesized and then screened for their in vitro urease, α-glucosidase, and acetylcholinesterase inhibition properties for the first time. All the synthesized compounds showed an outstanding urease inhibitory effect when compared with standards. Compounds 1 , 4 , 5b , 5d , 6b , 6d , 7b , and 7d showed significant acetylcholinesterase inhibitory activity with IC₅₀ values between 7.32 ± 0.58 and 12.52 ± 0.13 μg/ml comparable to donepezil (15.12 ± 0.20 μg/ml). Compound 5c , having thiosemicarbazide moiety at the positions N-1 and N-3 of benzimidazolone nucleus, showed the highest α-glucosidase inhibitory activity (IC₅₀ = 11.42 ± 0.11 μg/ml).     

Tyrosinase inhibitory constituents from the bark of Peltophorum dasyrachis (yellow batai)

Tyrosinase inhibitory activity-guided fractionation of the bark of Peltophorum dasyrachis (yellow batai) led to the isolation of the six active compounds which were characterised as six flavonoids: apigenin (1), (+)-2,3-trans-dihydrokaempferol (2), (+)-2,3-trans-dihydrokaempferol-3-O-α-L-rhamnoside (3), (+)-4',7-dimethoxy-2,3-trans-dihydroquercetin (4), (+)-2,3-trans-dihydroquercetin (5) and (-)-2,3-trans-dihydroquercetin-3-O-α-L-rhamnoside (6). All compounds were isolated for the first time from the bark of P. dasyrachis. Moreover, all compounds were evaluated for tyrosinase activities towards L-DOPA as the substrate. We observed that compounds 2 and 5 showed potent inhibitory effects (IC?? values were 126?±?3.2 and 210?±?5.8?μM, respectively). In general, for flavonoids the 3',4'-dihydroxy group's substituent is a more potent inhibitor than the 4'-hydroxy group substituent, i.e. quercetin?>?kaempferol. Interestingly, our result in the oxidation of L-DOPA showed that the 4'-hydroxy group substituent (compound 2) is a more potent inhibitor than the 3',4'-dihydroxy group substituent (compound 5). This result showed a new relationship between tyrosinase inhibitory activities and flavonoids. The kinetic analyses by Lineweaver-Burk plots showed that both the compounds 2 and 5 behaved as competitive inhibitors of L-DOPA oxidation.     

Indoline derivatives II: synthesis and factor Xa (FXa) inhibitory activities

Factor Xa (FXa) is well known to play a pivotal role in blood coagulation, so FXa inhibitor is a promising drug candidate for prophylaxis and treatment of thromboembolic diseases. In the course of our research, we have found that (R)-5-[1-(acetimidoyl)piperidin-4-yloxy]-2-(7-amidinonaphthalen-2-yl)-1-(ethanesulfonyl)indoline ((R)-1) showed potent FXa inhibitory activity in vitro. However, single oral administation (RS)-1 showed high toxicity in mice. Among newly synthesized compounds, ({(RS)-5-[1-(acetimidoyl)piperidin-4-yloxy]-2-(7-amidinonaphthalen-2-yl)indolin-1-yl}sulfonyl)acetic acid ((RS)-11d) showed more potent FXa inhibitory activity and higher safety than (RS)-1. The R-isoform of compound 11d ((R)-11d) exhibited potent in vitro anticoagulant activity in human and hamster plasma. Orally administered (R)-11d also showed dose-dependent potent anticoagulant activity in hamsters, marmosets and cynomolgus monkeys. Compound (R)-11d with potent anticoagulant activity and high safety is therefore favorable as a novel oral FXa inhibitor.     

Molecular modelling and enzymatic studies of acetylcholinesterase and butyrylcholinesterase recognition with paraquat and related compounds

The potent herbicide paraquat and three other analogues MPP+, MPDP+ and MPTP have a known toxicological profile linked to the ability to damage dopaminergic neurons. Other biological effects were recently addressed to this class of compounds, including the ability to interact with enzymatic targets involved in the Central Nervous System, such as the acetylcholinesterase (AChE) and the butyrylcholinesterase (BuChE). A combined molecular modelling and enzymatic study focusing onto their interaction against the AChE and BuChE is reported. The former study was performed by docking techniques using target known co-crystallographic models. The latter study was carried out by the widely adopted Ellman's method. In both studies the anti-Alzheimer FDA approved drug tacrine was used as reference inhibitor. Our results indicate that paraquat, MPTP, MPDP+ and MPP+ recognize both enzymatic cleft in a similar fashion compared to the reference inhibitor. A structure-activity correlation was found with the net charge of the ligands, indicating a major role of the electrostatic term in the recognition and inhibition of these compounds. Our data completed their enzymatic profile, added new information on the molecular mechanisms underlying their neurotoxicity useful for the rational design of new cholinesterase inhibitors.     

Dual inhibitors of Interleukin-6 and acetylcholinesterase for treatment of Alzheimer's disease: Design,docking, synthesis and biological evaluation

Multitarget compounds intercept two or more functionally complementary pathways simultaneously, and are therefore considered to have potential in effectively treating complex multifactorial diseases like Alzheimer's disease (AD). In the present study, novel molecules are designed by coupling a chromone and a N,N-disubstituted carbamoyl amine as pharmacophore for interleukin-6 (IL-6) and acetylcholinesterase (AChE) inhibition, respectively. Four series (Y1–Y4) of 40 compounds are designed by using alkyl linkers of different lengths (1–4 carbon atoms) for the coupling of the two selected pharmacophore. Docking of all designed compounds in AChE leads to the identification of twelve best fit compounds (Docking score >8.3). The data suggests that a 1- or 2-carbon atom linker is the most conducive to orient the pharmacophore for optimum binding with AChE active site. The predicted ADME properties of the 12 selected compounds suggest that these can cross the blood brain barrier (BBB) with good oral bioavailability. These compounds are synthesised and evaluated for anti-AChE activity. Five compounds, showing >45% inhibition of AChE, are further evaluated for IL-6 inhibitory activity. Compound Y1f is found to be the most potent inhibitor of both AChE and IL-6 (IC₅₀ 0.7 and 0.8 ​μM, respectively). It suggests that a chromone moiety connected to a piperidine ring through a 1-carbon atom linker may provide a useful template to medical chemists for the development of new chemical entities effective against AD.     

Multiwell fluorometric and colorimetric microassays for the evaluation of beta-secretase (BACE-1) inhibitors

The amyloid beta (Abeta) peptide is responsible for toxic amyloid plaque formation and is central to the aetiology of Alzheimer’s disease (AD). It is generated by proteolytic processing of the amyloid precursor protein (APP) by beta-secretase (BACE-1) and gamma-secretase. Consequently, inhibition of BACE-1, a rate-limiting enzyme in the production of Abeta, is an attractive therapeutic approach to the treatment of Alzheimer’s disease. This paper reports on improved microtiter plate-based fluorescence and colorimetric assays for the high-throughput screening (HTS) of BACE-1 inhibitors achieved by employing, for the first time, casein fluorescein isothiocyanate (casein-FITC) and N-α-benzoyl-D,L-arginine p-nitroanilide (BAPNA) as substrates, since they are known to be readily available and convenient substrates for proteases. The methods are based on the fluorescence enhancement following casein-FITC proteolysis and the visible absorbance of the p-nitroaniline (pNA) produced by BAPNA hydrolysis, with both reactions catalysed by BACE-1. Casein-FITC is a high-affinity substrate (K _m = 110 nM) for BACE-1, more so than the Swedish (SW) type peptide (a peptide containing the Swedish mutant of APP, a familiar mutation that enhances Abeta production). BACE-1 catalysis of casein-FITC proteolysis exhibited Michaelis–Menten kinetic. Therefore, it was found that BACE-1 was saturable with casein-FITC that was processed in a time- and pH-dependent manner with greater catalytic efficiency than observed for the SW peptide. The enantioselective hydrolysis of L-BAPNA by BACE-1 was observed. l-BAPNA was hydrolysed ten times more efficiently by BACE-1 than the WT (wild-type peptide). The novel methods were validated using a FRET assay as an independent reference method. Therefore, in order to select new leads endowed with multifunctional activities, drugs for Alzheimer’s disease (AD)—potent acetylcholinesterase (AChE) inhibitors—were tested for BACE-1 inhibition using the proposed validated assays. Among these, donepezil, besides being an acetylcholinesterase inhibitor, was also found to be a BACE-1 inhibitor that displayed submicromolar potency (170 nM).     

Attenuating effect of bioactive coumarins from Convolvulus pluricaulis on scopolamine-induced amnesia in mice

Convolvulus pluricaulis Chois. (Convolvulaceae) has been used in Ayurveda as Medhya Rasyana (nervine tonic) to treat various mental disorders. This study was designed to isolate the bioactive compound(s) of this plant and to evaluate their effect against scopolamine-induced amnesia. Column chromatography of the chloroform and ethyl-acetate fractions led to the isolation of three coumarins identified as scopoletin, ayapanin and scopolin. All the three compounds at 2.5, 5, 10 and 15 mg/kg, p.o. were evaluated for memory-enhancing activity against scopolamine-induced amnesia using elevated plus maze and step down paradigms. Effect on acetylcholinesterase activity in mice brain was also evaluated. Scopoletin and scopolin, in both the paradigms, significantly and dose dependently attenuated the scopolamine-induced amnesic effect. Furthermore, these compounds at 10 and 15 mg/kg exhibited activity comparable to that of standard drug, donepezil. The compounds also exhibited significant acetylcholinesterase inhibitory activity.