Design,synthesis and preliminary structure–activity relationship investigation of nitrogen-containing chalcone derivatives as acetylcholinesterase and butyrylcholinesterase inhibitors: a further study based on Flavokawain B Mannich base derivatives

In order to study the structure–activity relationship of Flavokawain B Mannich-based derivatives as acetylcholinesterase (AChE) inhibitors in our recent investigation, 20 new nitrogen-containing chalcone derivatives (4?a–8d) were designed, synthesized, and evaluated for AChE inhibitory activity in vitro. The results suggested that amino alkyl side chain of chalcone dramatically influenced the inhibitory activity against AChE. Among them, compound 6c revealed the strongest AChE inhibitory activity (IC₅₀ value: 0.85?μmol/L) and the highest selectivity against AChE over BuChE (ratio: 35.79). Enzyme kinetic study showed that the inhibition mechanism of compound 6c against AChE was a mixed-type inhibition. The molecular docking assay showed that this compound can both bind with the catalytic site and the peripheral site of AChE.     

Structure–activity relationship investigation of benzamide and picolinamide derivatives containing dimethylamine side chain as acetylcholinesterase inhibitors

A series of benzamide and picolinamide derivatives containing dimethylamine side chain (4a–4c and 7a–7i) were synthesised and evaluated for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activity in vitro. Structure–activity relationship investigation revealed that the substituted position of dimethylamine side chain markedly influenced the inhibitory activity and selectivity against AChE and BChE. In addition, it seemed that the bioactivity of picolinamide amide derivatives was stronger than that of benzamide derivatives. Among them, compound 7a revealed the most potent AChE inhibitory activity (IC₅₀: 2.49?±?0.19?μM) and the highest selectivity against AChE over BChE (Ratio: 99.40). Enzyme kinetic study indicated that compound 7a show a mixed-type inhibition against AChE. The molecular docking study revealed that this compound can bind with both the catalytic site and the peripheral site of AChE.     

Design, synthesis and evaluation of isaindigotone derivatives as acetylcholinesterase and butyrylcholinesterase inhibitors

A series of isaindigotone derivatives 5a-d and 6a-d were designed, synthesized and evaluated as acetylcholinesterase and butyrylcholinesterase inhibitors. Results showed that the novel class of isaindigotone derivatives could inhibit both cholinesterases and the selectivity of AChE over BuChE inhibition was related to the aromatic, the species and length of the alkyl amino side chain of compounds. The structure-activity relationships were discussed and their multiple binding modes were further clarified in the molecular docking studies.     

Structure–activity relationship investigation of tertiary amine derivatives of cinnamic acid as acetylcholinesterase and butyrylcholinesterase inhibitors: compared with that of phenylpropionic acid,sorbic acid and hexanoic acid

In the present investigation, 48 new tertiary amine derivatives of cinnamic acid, phenylpropionic acid, sorbic acid and hexanoic acid (4d–6g, 10d–12g, 16d–18g and 22d–24g) were designed, synthesized and evaluated for the effect on AChE and BChE in vitro. The results revealed that the alteration of aminoalkyl types and substituted positions markedly influences the effects in inhibiting AChE. Almost of all cinnamic acid derivatives had the most potent inhibitory activity than that of other acid derivatives with the same aminoalkyl side chain. Unsaturated bond and benzene ring in cinnamic acid scaffold seems important for the inhibitory activity against AChE. Among them, compound 6g revealed the most potent AChE inhibitory activity (IC₅₀ value: 3.64?µmol/L) and highest selectivity over BChE (ratio: 28.6). Enzyme kinetic study showed that it present a mixed-type inhibition against AChE. The molecular docking study suggested that it can bind with the catalytic site and peripheral site of AChE.     

Acetylcholinesterase inhibitors for potential use in Alzheimer's disease: molecular modeling, synthesis and kinetic evaluation of 11H-indeno-[1,2-b]-quinolin-10-ylamine derivatives

Continuing our work on tetracyclic tacrine analogues, we synthesized a series of acetylcholinesterase (AChE) inhibitors of 11H-indeno-[1,2-b]-quinolin-10-ylaminic structure. Selected substituents were placed in synthetically accessible positions of the tetracyclic nucleus, in order to explore the structure-activity relationships (SAR) and the mode of action of this class of anticholinesterases. A molecular modeling investigation of the binding interaction of the lead compound (1a) with the AChE active site was performed, from which it resulted that, despite the rather wide and rigid structure of 1a, there may still be the possibility to introduce some small substituent in some positions of the tetracycle. However, from the examination of the experimental IC50 values, it derived that the indenoquinoline nucleus probably represents the maximum allowable molecular size for rigid compounds binding to AChE. In fact, only a fluorine atom in position 2 maintains the AChE inhibitory potency of the parent compound, and, actually, increases the AChE-selectivity with respect to the butyrylcholinesterase inhibition. By studying the kinetics of AChE inhibition for two representative compounds of the series, it resulted that the lead compound (1a) shows an inhibition of mixed type, binding to both the active and the peripheral sites, while the more sterically hindered analogue 2n seems to interact only at the external binding site of the enzyme. This finding seems particularly important in the context of Alzheimer's disease research in the light of recent observations showing that peripheral AChE inhibitors might decrease the aggregating effects of the enzyme on the beta-amyloid peptide (betaA).     

Computational studies of acetylcholinesterase complexed with fullerene derivatives: a new insight for Alzheimer disease treatment

Here, we propose five fullerene (C60) derivatives as new drugs against Alzheimer’s disease (AD). These compounds were designed to act as new human acetylcholinesterase (HssAChE) inhibitors by blocking its fasciculin II (FASII) binding site. Docking and molecular dynamic results show that our proposals bind to the HssAChE tunnel entrance, forming stable complex, and further binding free energy calculations suggest that three of the derivatives proposed here could be potent HssAChE inhibitors. We found a region formed by a set of residues (Tyr72, Asp74, Trp286, Gln291, Tyr341, and Pro344) which can be further exploited in the drug design of new inhibitors of HssAChE based on C60 derivatives. Results presented here report for the first time by a new class of molecules that can become effective drugs against AD.     

Kinetic and structural studies on the interactions of Torpedo californica acetylcholinesterase with two donepezil-like rigid analogues

Acetylcholinesterase inhibitors were introduced for the symptomatic treatment of Alzheimer’s disease (AD). Among the currently approved inhibitors, donepezil (DNP) is one of the most preferred choices in AD therapy. The X-ray crystal structures of Torpedo californica AChE in complex with two novel rigid DNP-like analogs, compounds 1 and 2, have been determined. Kinetic studies indicated that compounds 1 and 2 show a mixed-type inhibition against TcAChE, with K_i values of 11.12?±?2.88 and 29.86?±?1.12?nM, respectively. The DNP rigidification results in a likely entropy-enthalpy compensation with solvation effects contributing primarily to AChE binding affinity. Molecular docking evidenced the molecular basis for the binding of compounds 1 and 2 to the active site of β-secretase-1. Overall, these simplified DNP derivatives may represent new structural templates for the design of lead compounds for a more effective therapeutic strategy against AD by foreseeing a dual AChE and BACE-1 inhibitory activity.     

Synthesis of α-oxycarbanilinophosphonates and their anticholinesterase activities: the most potent derivative is bound to the peripheral site of acetylcholinesterase

A novel method has been developed for the synthesis of α-oxycarbanilino phosphonates through a reaction of α-hydroxyphosphonates with isocyanate under microwave irradiation. The synthesized compounds were evaluated for their acetylcholinesterase (AChE) inhibition potency through IC₅₀determination. Molecular modelling studies suggest that the most potent inhibitor (compound 4h, IC₅₀ = 6.36 µM) is bound to the peripheral site of AChE, which suggests that it decreases the catalytic activity not through binding to the active site but through blocking the entrance of the active site gorge. This puts forward the potential of compound 4h and its derivatives to be used in the design of dual inhibitors: inhibition of the catalytic activity of AChE and of amyloid β aggregation.     

Design,synthesis and evaluation of quinolinone derivatives containing dithiocarbamate moiety as multifunctional AChE inhibitors for the treatment of Alzheimer’s disease

Abstract

A series of novel quinolinone derivatives bearing dithiocarbamate moiety were designed and synthesised as multifunctional AChE inhibitors for the treatment of AD. Most of these compounds exhibited strong and clearly selective inhibition to eeAChE. Among them, compound 4c was identified as the most potent inhibitor to both eeAChE and hAChE (IC₅₀ = 0.22?μM for eeAChE; IC₅₀ = 0.16?μM for hAChE), and it was also the best inhibitor to AChE-induced Aβ aggregation (29.02% at 100?μM) and an efficient inhibitor to self-induced Aβ aggregation (30.67% at 25?μM). Kinetic and molecular modelling studies indicated that compound 4c was a mixed-type inhibitor, which could interact simultaneously with the catalytic anionic site (CAS) and the peripheral anionic site (PAS) of AChE. In addition, 4c had good ability to cross the BBB, showed no toxicity on SH-SY5Y neuroblastoma cells and was well tolerated in mice at doses up to 2500?mg/kg (po).     

Synthesis,biological evaluation,and molecular modeling of berberine derivatives as potent acetylcholinesterase inhibitors

By targeting the dual active sites of acetylcholinesterase (AChE), a new series of berberine derivatives was designed, synthesized, and evaluated as AChE inhibitors. Most of the derivatives inhibited AChE in the sub-micromolar range. Compound 8c, berberine linked with phenol by a 4-carbon spacer, showed the most potent inhibition of AChE. A kinetic study of AChE and BuChE indicated that a mix-competitive binding mode existed for these berberine derivatives. Molecular modeling studies confirmed that these hybrids target both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE. This is the first report where AChE inhibitory activity has been associated with berberine as a lead molecule.     

Design,synthesis and cholinesterase inhibitory properties of new oxazole benzylamine derivatives

Abstract

The enzymes acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are primary targets in attenuating the symptoms of neurodegenerative diseases. Their inhibition results in elevated concentrations of the neurotransmitter acetylcholine which supports communication among nerve cells. It was previously shown for trans-4/5-arylethenyloxazole compounds to have moderate AChE and BChE inhibitory properties. A preliminary docking study showed that elongating oxazole molecules and adding a new NH group could make them more prone to bind to the active site of both enzymes. Therefore, new trans-amino-4-/5-arylethenyl-oxazoles were designed and synthesised by the Buchwald-Hartwig amination of a previously synthesised trans-chloro-arylethenyloxazole derivative. Additionally, naphthoxazole benzylamine photoproducts were obtained by efficient photochemical electrocyclization reaction. Novel compounds were tested as inhibitors of both AChE and BChE. All of the compounds exhibited binding preference for BChE over AChE, especially for trans-amino-4-/5-arylethenyl-oxazole derivatives which inhibited BChE potently (IC₅₀ in µM range) and AChE poorly (IC₅₀?100?µM). Therefore, due to the selectivity of all of the tested compounds for binding to BChE, these compounds could be applied for further development of cholinesterase selective inhibitors.

• HIGHLIGHTS

• Series of oxazole benzylamines were designed and synthesised

• The tested compounds showed binding selectivity for BChE

• Naphthoxazoles were more potent AChE inhibitors

     

Interaction of an organophosphate with a peripheral site on acetylcholinesterase

O-Ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (MPT) is an active site directed inhibitor of acetylcholinesterase (AChE). Inhibition of the Electrophorus electricus (G4) enzyme follows classical second-order kinetics. However, inhibition of total mouse skeletal muscle AChE and inhibition of the individual molecular forms from muscle, including the monomeric species, do not proceed as simple irreversible bimolecular reactions. Similarly, complex inhibition kinetics are observed for the purified enzyme from Torpedo californica. AChE can be cross-linked with glutaraldehyde into a semisolid matrix. Under these conditions the abnormal concentration dependence for MPT inhibition is accentuated, and a range of MPT concentrations can be found where inhibition of polymerized AChE is far less than that observed at lower concentrations. Inhibition in certain concentration ranges is partially reversible after removal of all unbound ligand. Thus, there are two different modes of organophosphorus inhibition by MPT: the classical irreversible phosphorylation of the active site and a reversible interaction at a site peripheral to the active center. Propidium, a well-studied peripheral site ligand, can prevent the later interaction. Hence, the second site of MPT interaction with AChE may overlap or be linked to the peripheral anionic site of AChE characterized by the binding of propidium and other peripheral site inhibitors.     

Structural insights into ligand interactions at the acetylcholinesterase peripheral anionic site

The peripheral anionic site on acetylcholinesterase (AChE), located at the active center gorge entry, encompasses overlapping binding sites for allosteric activators and inhibitors; yet, the molecular mechanisms coupling this site to the active center at the gorge base to modulate catalysis remain unclear. The peripheral site has also been proposed to be involved in heterologous protein associations occurring during synaptogenesis or upon neurodegeneration. A novel crystal form of mouse AChE, combined with spectrophotometric analyses of the crystals, enabled us to solve unique structures of AChE with a free peripheral site, and as three complexes with peripheral site inhibitors: the phenylphenanthridinium ligands, decidium and propidium, and the pyrogallol ligand, gallamine, at 2.20-2.35 A resolution. Comparison with structures of AChE complexes with the peptide fasciculin or with organic bifunctional inhibitors unveils new structural determinants contributing to ligand interactions at the peripheral site, and permits a detailed topographic delineation of this site. Hence, these structures provide templates for designing compounds directed to the enzyme surface that modulate specific surface interactions controlling catalytic activity and non-catalytic heterologous protein associations.     

Design,synthesis and biological evaluation of selected 3-[3-(amino) propoxy] benzenamines as acetylcholinesterase inhibitors

The present paper describes design, synthesis, and biological evaluation of a series of some 3-[3-(amino)propoxy]benzenamines as acetylcholinesterase inhibitors using mice as a model and piracetam as a reference drug. The structures of these compounds were confirmed by spectral analysis and compounds were tested for memory enhancing activity using elevated plus maze test and acetylcholinesterase inhibitory assay. The inhibitory range of synthesized compounds was from 8.99 to 28.31 μM. The synthesized compounds possessed higher or equivalent percent retention as compared to piracetam at 1 mg/kg with no other CNS-related activities (locomotor and muscle relaxant, analgesic and anticonvulsant activities). Compound 3-[3-(imidazolo)propoxy]benzenamine has shown significant dose-dependent (1 and 3 mg/kg) memory enhancing activity, while 3-[3-(pyrrolidino)propoxy]benzenamine also showed activity equivalent to reference drug piracetam at 1 mg/kg. Both compounds 3-[3-(pyrrolidino)propoxy]benzenamine and 3-[3-(imidazolo)propoxy]benzenamine were also found to show AChE inhibition with IC₅₀ value of 8.99 and 17.87 μM. The molecular docking, MM-GBSA and molecular dynamics simulation studies were performed in order to establish a relationship between the biological results. RMSD, root-mean-square fluctuations, and interaction patterns of 10a–AChE and Sck–AChE complexes proved that the binding affinity of 10a toward AChE was highly stable with the proposed binding orientations.     

Synthesis and biological evaluation of novel flavonoid derivatives as dual binding acetylcholinesterase inhibitors

A new series of flavonoid derivatives have been designed, synthesised and evaluated as acetylcholinesterase inhibitors that could bind simultaneously to the peripheral and catalytic sites of the enzyme. Among them, fifteen derivatives were found to inhibit the enzyme in the micromolar range and isoflavone derivatives possessed more potent inhibitory activity than other flavonoid derivatives. The best compound 9a had its inhibitory activity (IC₅₀ = 0.093μM) in the same range as the reference compound, donepezil (IC₅₀ = 0.025μM). Preliminary structure-activity relationships and a molecular modeling study for 9a have revealed that the isoflavone moiety plays a key role in the interaction of this series of derivatives with AChE by acting as an anchor in its peripheral anionic site.     

3D-QSAR analysis of a new type of acetylcholinesterase inhibitors

Acetylcholinesterase (AChE) inhibitors are an important class of medicinal agents used for the treatment of Alzheimer’s disease. A screening model of AChE inhibitor was used to evaluate the inhibition of a series of phenyl pentenone derivatives. The assay result showed that some compounds displayed higher inhibitory effects. In order to study the relationship between the bioactivities and the structures, 26 compounds with phenyl pentenone scaffold were analyzed. A 3D-QSAR model was constructed using the method of comparative molecular field analysis (CoMFA). The results of cross-validated R²cv=0.629, non-cross-validated R²=0.972, SE=0.331, and F=72.41 indicate that the 3D-model possesses an ability to predict the activities of new inhibitors, and the CoMFA model would be useful for the future design of new AChE inhibitors.     

Targeting acetylcholinesterase: identification of chemical leads by high throughput screening, structure determination and molecular modeling

Acetylcholinesterase (AChE) is an essential enzyme that terminates cholinergic transmission by rapid hydrolysis of the neurotransmitter acetylcholine. Compounds inhibiting this enzyme can be used (inter alia) to treat cholinergic deficiencies (e.g. in Alzheimer''s disease), but may also act as dangerous toxins (e.g. nerve agents such as sarin). Treatment of nerve agent poisoning involves use of antidotes, small molecules capable of reactivating AChE. We have screened a collection of organic molecules to assess their ability to inhibit the enzymatic activity of AChE, aiming to find lead compounds for further optimization leading to drugs with increased efficacy and/or decreased side effects. 124 inhibitors were discovered, with considerable chemical diversity regarding size, polarity, flexibility and charge distribution. An extensive structure determination campaign resulted in a set of crystal structures of protein-ligand complexes. Overall, the ligands have substantial interactions with the peripheral anionic site of AChE, and the majority form additional interactions with the catalytic site (CAS). Reproduction of the bioactive conformation of six of the ligands using molecular docking simulations required modification of the default parameter settings of the docking software. The results show that docking-assisted structure-based design of AChE inhibitors is challenging and requires crystallographic support to obtain reliable results, at least with currently available software. The complex formed between C5685 and Mus musculus AChE (C5685•mAChE) is a representative structure for the general binding mode of the determined structures. The CAS binding part of C5685 could not be structurally determined due to a disordered electron density map and the developed docking protocol was used to predict the binding modes of this part of the molecule. We believe that chemical modifications of our discovered inhibitors, biochemical and biophysical characterization, crystallography and computational chemistry provide a route to novel AChE inhibitors and reactivators.     

Simple chalcones and bis-chalcones ethers as possible pleiotropic agents

The synthesis, the antioxidative properties and the lipoxygenase (LOX) and acetylcholinesterase (AChE) inhibition of a number of 4-hydroxy-chalcones diversely substituted as well as of a series of bis-chalcones ether derivatives are reported. The chalcones derivatives were readily produced using a Claisen–Schmidt condensation in a ultra sound bath in good yields. The structures of the synthesized compounds were confirmed by spectral and elemental analysis. Their lipophilicity is experimentally determined by reversed-phase thin-layer chromatography method. Most of them are potent in vitro inhibitors of lipid peroxidation and of LOX. Compounds b2 and b3 were found to be the most potent LOX and AChE inhibitors among the tested derivatives with a significant anti-lipid peroxidation profile. The results led us to propose these enone derivatives as new multifunctional compounds against Alzheimer's disease. The results are discussed in terms of structural and physicochemical characteristics of the compounds. Moreover, the pharmacokinetic profile of these compounds was investigated using computational methods.     

Design, synthesis and evaluation of isaindigotone derivatives as dual inhibitors for acetylcholinesterase and amyloid beta aggregation

A series of isaindigotone derivatives and analogues were designed, synthesized and evaluated as dual inhibitors of cholinesterases (ChEs) and self-induced β-amyloid (Aβ) aggregation. The synthetic compounds had IC(50) values at micro or nano molar range for cholinesterase inhibition, and some compounds exhibited strong inhibitory activity for AChE and high selectivity for AChE over BuChE, which were much better than the isaindigotone derivatives previously reported by our group. Most of these compounds showed higher self-induced Aβ aggregation inhibitory activity than a reference compound curcumin. The structure-activity relationship studies revealed that the derivatives with higher inhibition activity on AChE also showed higher selectivity for AChE over BuChE. Compound 6c exhibiting excellent inhibition for both AChE and self-induced Aβ aggregation was further studied using CD, EM, molecular docking and kinetics.     

2-(2-indolyl-)-4(3H)-quinazolines derivates as new inhibitors of AChE: design,synthesis, biological evaluation and molecular modelling

We recently reported that synthetic derivatives of rutaecarpine alkaloid exhibited high acetyl cholinesterase (AChE) inhibitory activity and high selectivity for AChE over butyrylcholinesterases (BuChE). To explore novel effective drugs for the treatment of Alzheimer’s disease (AD), in this paper, further research results were presented. Starting from a structure-based drug design, a series of novel 2-(2-indolyl-)-4(3H)-quinazolines derivates were designed and synthesized as the ring-opened analogues of rutaecarpine alkaloid and subjected to pharmacological evaluation as AChE inhibitors. Among them, derivates 3a–c and 3g–h exhibited strong inhibitory activity for AChE and high selectivity for AChE over BuChE. The structure–activity relationships were discussed and their binding conformation and simultaneous interactions mode were further clarified by kinetic characterization and the molecular docking studies.