Isoquinoline derivatives as potential acetylcholinesterase inhibitors

Several bisbenzylisoquinoline alkaloid derivatives showed the inhibitory activity at acetylcholinesterase enzyme (AChE) in micromolar range. It is possible that monomeric moiety of bisbenzylisoquinoline alkaloid might be required for acetylcholinesterase enzyme inhibition. AChE inhibitory activity of related monomeric 1-benzylisoquinolines was examined by using Ellman colorimetric assay with galanthamine as a reference standard.     

Silicon compounds as substrates and inhibitors of acetylcholinesterase

Several trimethylsilyl derivatives were found to be ligands of acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7): trimethylsilylethyl acetate (III) and trimethylsilylmethyl acetate (V) are substrates of the enzyme, whereas trimethylsilylethanol (VIII) is a competitive inhibitor. The silicon compounds have kinetic parameters similar to those of their carbon analogues, except for trimethylsilylmethyl acetate, which is a substrate of acetylcholinesterase, whereas its carbon analogue is not susceptible to enzymic hydrolysis.     

New acrylamide-sulfisoxazole conjugates as dihydropteroate synthase inhibitors

New functionalized acrylamide derivatives bearing sulfisoxazole moiety were designed to target bacterial dihydropteroate synthase (DHPS). The in vitro antimicrobial activities of these compounds were assessed. The E-configuration of compound 5b was proved by single crystal X-ray analysis. Compounds 5g and 5h displayed double the activity of ampicillin against B. subtilis. Also, 5h was two times more active than gentamycin against E. coli. Interestingly, compounds 5f-g, 7c, 8a, 8c exhibited two folds the potency of amphotericin B against S. racemosum while 5h displayed three folds the activity of amphotericin B against S. racemosum. Most of the synthesized compounds showed superior activities to the parent sulfisoxazole and were non-toxic to normal cells. DHPS is confirmed to be a putative target for our compounds via antagonizing their antibacterial activity by the folate precursor (p-aminobenzoic acid) and product (methionine) on E. coli ATCC 25922. Docking experiments against DHPS rationalized the observed antibacterial activity. Additionally, compound 5g was evaluated as a selective targeting vector for ^99mTc that showed a remarkable uptake and targeting ability towards the infection site that was induced in mice.     

Some new carbacylamidophosphates as inhibitors of acetylcholinesterase and butyrylcholinesterase

The differences in the inhibition activity of organophosphorus agents are a manifestation of different molecular properties of the inhibitors involved in the interaction with the active site of enzyme. We were interested in comparing the inhibition potency of four known synthesized carbacylamidophosphates with the general formula RC(O)NHP(O)Cl2, constituting organophosphorus compounds, where R = CCl3 (1), CHCl2 (2), CH2Cl (3) and CF3 (4), and four new ones with the general formula RC(O)NHP(O)(R')2, where R' = morpholine and R = CCl3 (5), CHCl2 (6), CH2Cl (7), CF3 (8), on AChE and BuChE activities. In addition, in vitro activities of all eight compounds on BuChE were determined. Besides, in vivo inhibition potency of compounds 2 and 6, which had the highest inhibition potency among the tested compounds, was studied. The data demonstrated that compound 2 from the compound series 1 to 4 and compound 6 from the compound series 5 to 8 are the most sensitive as AChE and BuChE inhibitors, respectively. Comparing the IC50 values of these compounds, it was clear that the inhibition potency of these compounds for AChE are 2- to 100-fold greater than for BuChE inhibition. Comparison of the kinetics (IC50, Ki, kp, KA and KD) of AChE and BuChE inactivation by these compounds resulted in no significant difference for the measured variables except for compounds 2 and 6, which appeared to be more sensitive to AChE and BuChE by significantly higher kp and Ki values and a lower IC50 value in comparison with the other compounds. The LD50 value of compounds 2 and 6, after oral administration, and the changes of erythrocyte AChE and plasma BuChE activities in albino mice were studied. The in vivo experiments, similar to the in vitro results, showed that compound 2 is a stronger AChE and BuChE inhibitor than the other synthesized carbacylamidophosphates. Furthermore, in this study, the importance of electropositivity of the phosphorus atom, steric hindrance and leaving group specificity were reinforced as important determinants of inhibition activity.     

Insect pheromones as reversible competitive inhibitors of acetylcholinesterase

Summary

Structural aspects of insect pheromones, especially their hydrophobicity, prompted the examination of them by in vitro and in vivo experiments as inhibitors of acetylcholinesterase. All 17 pheromones assayed in sufficient detail were reversible, competitive inhibitors of acetylcholinesterase: K_i values ranged from 0.27 mM for frontalin to 9.3 mM for ipsenol, both aggregation pheromones. All seven pheromones assayed with Tribolium castaneum immobilised this species with an effect that was weakly dose-responsive over the range of concentrations tested. Concentrations eliciting 25% immobility (IC₂₅) ranged from 2.0x10³ ppm for 3-methy 1–2-cyclohexenone to 2.0x10⁴ ppm for cis-7, cis-11-hexadecadien-1-yl acetate, both sex attractants. Such efficacies suggest that the pheromones tested would be effective as defence agents only in species living in a confined area, as under bark, or in aggregations.     

Screening of non-alkaloidal natural compounds as acetylcholinesterase inhibitors

Acetylcholinesterase (AChE) inhibitors are currently the only approved therapy for the treatment of Alzheimer's disease, only a limited number of drugs are commercially available. A library of non-alkaloidal natural compounds was investigated. To this end, a convenient microtitre plate method for assaying AChE inhibition, which allows a complete kinetic analysis of AChE inhibitors, was developed. Seven active compounds with Ki values in the micromolar range were identified, six of which were xanthones. This is the first report that a promising potential for AChE inhibition exists in such non-nitrogenous natural compounds. Furthermore, four xanthones among these xanthones had already been described as monoamine oxidase (MAO) inhibitors, making then dual AChE/MAO inhibitors of great interest.     

Novel isosorbide di-ester compounds as inhibitors of acetylcholinesterase

We report herein that a variety of isosorbide di-esters, previously reported to be novel substrates for butyrylcholinesterase (BuChE, EC 3.1.1.8), are in fact inhibitors of the homologous enzyme acetylcholinesterase (AChE), with IC(50) values in the micromolar range. In vitro studies show that they are mixed inhibitors of the enzyme, and thus the ternary enzyme-inhibitor-substrate complex can form in acetylcholinesterase. This is rationalised by molecular modelling which shows that the compounds bind in the mid-gorge area. In this position, simultaneous substrate binding might be possible, but the hydrolysis of this substrate is prevented. The di-esters dock within the butyrylcholinesterase gorge in a very different manner, with the ester sidechain at the 5-position occupying the acyl pocket at residues Leu286 and Val288, and the 2-ester binding to Trp82. The carbonyl group of the 2-ester is susceptible to nucleophilic attack by Ser198 of the catalytic triad. The larger residues of the acyl pocket in acetylcholinesterase prevent binding in this manner. The results complement each other and explain the differing behaviours of the esters in the cholinesterase enzymes. These findings may prove very significant for future work.     

Turrianes from Kermadecia rotundifolia as new acetylcholinesterase inhibitors

Four new kermadecins, together with the known kermadecins A, B and D have been isolated from the Kermadecia rotundifolia ethyl acetate bark extract. These compounds are derivatives of the (20-membered-o,-p)cyclophane skeleton and belong to the turriane family. The structures were elucidated by mass spectrometry, extensive one- and two-dimensional NMR spectroscopy and through comparison with data reported in the literature. Isokermadecin D (2) and kermadecins D and J (7 and 4) possess significant inhibitory effect on acetylcholinesterase.     

Novel dehydroabietylamine derivatives as potent inhibitors of acetylcholinesterase

Nowadays, the inhibition of acetylcholinesterase is one of the main pharmacological strategies for the treatment of Alzheimer’s disease. Therefore, a set of thirty-four derivatives of the diterpenoid dehydroabietylamine has been synthesized and screened in colorimetric Ellman’s assays to determine their ability to inhibit the enzymes acetylcholinesterase (AChE, from electric eel) and butyrylcholinesterase (BChE, from equine serum). A systematic variation of the substitution of dehydroabietylamides enabled an approach to analogs showing a remarkable inhibition potency for AChE. Particularly N-benzoyldehydroabietylamines 11, 12 and 13 were excellent inhibitors for AChE, showing inhibition rates comparable to standard galantamine hydrobromide.     

Synthesis of aminoalkyl-substituted coumarin derivatives as acetylcholinesterase inhibitors

Alzheimer’s disease, one of the most common forms of dementia, is a progressive neurodegenerative disorder symptomatically characterized by declines in memory and cognitive abilities. To date, the successful therapeutic strategy to treat AD is maintaining levels of acetylcholine by inhibiting acetylcholinesterase (AChE). In the present study, coumarin derivatives were designed and synthesized as AChE inhibitors based on the lead structure of scopoletin. Of those synthesized, pyrrolidine-substituted coumarins 3b and 3f showed ca. 160-fold higher AChE inhibitory activities than scopoletin. These compounds also ameliorated scopolamine-induced memory deficit in mice when administered orally at the dose of 1 and 2 mg/kg.     

ATP-phosphopeptide conjugates as inhibitors of Src tyrosine kinases

A number of Src SH2 domain inhibitors enhance the kinase catalytic activity by switching the closed inactive to the open active conformation. ATP-phosphopeptide conjugates were designed and synthesized as Src tyrosine kinase inhibitors based on a tetrapeptide sequence pTyr-Glu-Glu-Ile (pYEEI) and ATP to block the SH2 domain signaling and substrate phosphorylation by ATP, respectively. In general, ATP-phosphopeptide conjugates with optimal linkers such as compounds 5 and 7 (K(i) = 1.7-2.6 microM) showed higher binding affinities to the ATP-binding site relative to the other ATP-phosphopeptide conjugates having short or long linkers, 1-4 and 6, (K(i) = 10.1-16.1 microM) and ATP (K(m) = 74 microM). These ATP-phosphopeptide conjugates may serve as novel templates for designing protein tyrosine kinase inhibitors to block SH2 mediated protein-protein interactions and to counter the activation of enzyme that resulted from the SH2 inhibition.     

Porphyrin derivatives as inhibitors for acetylcholinesterase from Drosophila melanogaster

The cure for Alzheimer''s disease (AD) is still unknown. According to Cholinergic hypothesis, Alzheimer''s disease is caused by the reduced synthesis of the neurotransmitter, Acetylcholine. Regional cerebral blood flow can be increased in patients with Alzheimer''s disease by Acetylcholinesterase (AChE) inhibitors. In this regard, Tetraphenylporphinesulfonate (TPPS), 5,10,15,20- Tetrakis (4-sulfonatophenyl) porphyrinato Iron(III) Chloride (FeTPPS) and 5,10,15,20-Tetrakis (4-sulfonatophenyl) porphyrinatoIron(III) nitrosyl Chloride (FeNOTPPS) were investigated as candidate compounds for inhibition of Acteylcholinesterase of Drosophila melanogaster (DmAChE) by use of Molecular Docking. The results show that FeNOTPPS forms the most stable complex with DmAChE.     

New 3-O-substituted xanthone derivatives as promising acetylcholinesterase inhibitors

A new series of 3-O-substituted xanthone derivatives were synthesised and evaluated for their anti-cholinergic activities against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). The results indicated that the xanthone derivatives possessed good AChE inhibitory activity with eleven of them (5, 8, 11, 17, 19, 21-23, 26-28) exhibited significant effects with the IC₅₀ values ranged 0.88 to 1.28 µM. The AChE enzyme kinetic study of 3-(4-phenylbutoxy)-9H-xanthen-9-one (23) and ethyl 2-((9-oxo-9H-xanthen-3-yl)oxy)acetate (28) showed a mixed inhibition mechanism. Molecular docking study showed that 23 binds to the active site of AChE and interacts via extensive π–π stacking with the indole and phenol side chains of Trp86 and Tyr337, besides the hydrogen bonding with the hydration site and π–π interaction with the phenol side chain of Y72. This study revealed that 3-O-alkoxyl substituted xanthone derivatives are potential lead structures, especially 23 and 28 which can be further developed into potent AChE inhibitors.     

Novel racemic tetrahydrocurcuminoid dihydropyrimidinone analogues as potent acetylcholinesterase inhibitors

The synthesis of racemic tetrahydrocurcumin- (THC-), tetrahydrodemethoxycurcumin- (THDC-) and tetrahydrobisdemethoxycurcumin- (THBDC-) dihydropyrimidinone (DHPM) analogues was achieved by utilizing the multi-component Biginelli reaction in the presence of copper sulphate as a catalyst. The evaluation of acetylcholinesterase inhibitors for Alzheimer’s disease of these compounds showed that they exhibited higher inhibitory activity than their parent analogues. THBDC–DHPM demonstrated the most potent inhibitory activity with an IC₅₀ value of 1.34 ± 0.03 μM which was more active than the approved drug galanthamine (IC₅₀ = 1.45 ± 0.04 μM).     

Structure-activity study of phosphoramido acid esters as acetylcholinesterase inhibitors

Phosphoramido acid esters (CH(3))(2)NP(O)X(p-OC(6)H(4)-CH(3)) (containing P-Cl (1), P-O (2), P-F (3), P-CN (5), and P-N (4,6) bonds, X for 2, 4 and 6 is OCH(3), (C(2)H(5))(2)N and morpholin) have been synthesized to investigate the structure-activity study of AChE enzyme inhibition, through the parameters logP, delta(31)P and IC(50). After their characterization by (31)P, (31)P{(1)H}, (13)C, (1)H NMR, IR and mass spectroscopy, the parameters logP and delta(31)P ((31)P chemical shift in NMR) were used to evaluated the lipophilicity and electronical properties. The ability of compounds to inhibit human AChE was predicted by PASS software (version 1.193), and experimentally evaluated by a modified Ellman's assay.     

Substituted cinnamic anhydrides act as selective inhibitors of acetylcholinesterase

Cinnamic anhydrides have been shown to be more than reactive reagents, but they also act as inhibitors of the enzyme acetylcholinesterease (AChE). Thus, out of a set of 33 synthesised derivatives, several of them were mixed type inhibitors for AChE (from electric eel). Thus, (E)-3-(2,4-dimethoxyphenyl)acrylic anhydride (2c) showed K_i = 8.30 ± 0.94 µM and K_i′ = 9.54 ± 0.38 µM, and for (E)-3-(3-chlorophenyl)acrylic anhydride (2u) K_i = 8.23 ± 0.93 µM and K_i′ = 13.07 ± 0.46 µM were measured. While being not cytotoxic to many human cell lines, these compounds showed an unprecedented and noteworthy inhibitory effect for AChE but not for butyrylcholinesterase (BChE).     

Novel short oligonucleotide conjugates as inhibitors of human telomerase

A series of oligonucleotide conjugates were designed and synthesized as novel inhibitors of human telomerase. These compounds contain a relatively short (6-7-mer) oligonucleotide domain, with an N3'-->P5' phosphoramidate (np) or thio-phosphoramidate (nps) backbone, targeted to the template region of the RNA component of the enzyme and various pendant groups attached to either their 5'- or preferably to the 3'-termini. The most potent compounds in the series inhibited telomerase with low nM IC50 values in biochemical assays whereas the cognate oligonucleotides without the pendant groups were significantly less active having IC50 values 100-1000-fold higher.     

Bifunctional DNA-gold nanoparticle conjugates as building blocks for the self-assembly of cross-linked particle layers

The DNA-directed self-assembly of surface-bound layers of gold nanoparticles offers a broad range of applications in biomedical analyses as well as in materials science. We here describe a new concept for the assembly of substrate-bound nanoparticle monolayers which employs bifunctional nanoparticles as building blocks, containing two independently addressable DNA oligomer sequences. One of the sequences was utilized for attaching the particle at the solid support, while the other sequence was used to establish cross-links between adjacently immobilized particles. AFM analyses proved the functionality of inter-particle cross-links leading to enhanced surface coverages and the formation of monolayered supramolecular aggregates attached to the substrate. We anticipate that further refinement of this approach will enable applications, for instance, the assembly of ordered layers useful as transducers in biosensing.     

Synthesis and biological evaluation of naphthoquinone-coumarin conjugates as topoisomerase II inhibitors

Based on previous Topoisomerase II docking studies of naphthoquinone derivatives, a series of naphthoquinone-coumarin conjugates was synthesized through a multicomponent reaction from aromatic aldehydes, 4-hydroxycoumarin and 2-hydroxynaphthoquinone. The hybrid structures were evaluated against the α isoform of human topoisomerase II (hTopoIIα), Escherichia coli DNA Gyrase and E. coli Topoisomerase I. All tested compounds inhibited the hTopoIIα-mediated relaxation of negatively supercoiled circular DNA in the low micromolar range. This inhibition was specific since neither DNA Gyrase nor Topoisomerase I were affected. Cleavage assays pointed out that naphthoquinone-coumarins act by catalytically inhibiting hTopoIIα. ATPase assays and molecular docking studies further pointed out that the mode of action is related to the hTopoIIα ATP-binding site.