Design,synthesis and evaluation of tacrine–flurbiprofen–nitrate trihybrids as novel anti-Alzheimer’s disease agents

To search for multifunctional anti-Alzheimer’s disease (AD) agents with good safety, the previously synthesized tacrine–flurbiprofen hybrids 1a and 1b were modified into tacrine–flurbiprofen–nitrate trihybrids 3a–h. These compounds displayed comparable or higher cholinesterase inhibitory activity relative to the bivalent hybrids. Compound 3a was the most potent, which released moderate NO, exerted blood vessel relaxative activity, and showed significant Aβ inhibitory effects whereas tacrine and flurbiprofen did not exhibit any Aβ inhibitory activity at the same dose. In addition, 3a was active in improving memory impairment in vivo. More importantly, the hepatotoxicity study showed that 3a was much safer than tacrine, suggesting it might be a promising anti-AD agent for further investigation.     

Design,synthesis and biological activity of novel tacrine-isatin Schiff base hybrid derivatives

A series of novel tacrine-isatin Schiff base hybrid derivatives (7a-p) were designed, synthesized and evaluated as multi-target candidates against Alzheimer’s disease (AD). The biological assays indicated that most of these compounds displayed potent inhibitory activity toward acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) and specific selectivity for AChE over BuChE. It was also found that they act as excellent metal chelators. The compounds 7k and 7m were found to be good inhibitors of AChE-induced amyloid-beta (Aβ) aggregation. Most of the compounds inhibited AChE with the IC₅₀ values, ranging from 0.42 nM to 79.66 nM. Amongst them, 7k, 7m and 7p, all with a 6 carbon linker between tacrine and isatin Schiff base exhibited the strongest inhibitory activity against AChE with IC₅₀ values of 0.42 nM, 0.62 nM and 0.95 nM, respectively. They were 92-, 62- and 41-fold more active than tacrine (IC₅₀ = 38.72 nM) toward AChE. Most of the compounds also showed a potent BuChE inhibition among which 7d with an IC₅₀ value of 0.11 nM for BuChE is the most potent one (56-fold more potent than that of tacrine (IC₅₀ = 6.21 nM)). In addition, most compounds exhibited the highest metal chelating property. Kinetic and molecular modeling studies revealed that 7k is a mixed-type inhibitor, capable of binding to catalytic and peripheral site of AChE. Our findings make this hybrid scaffold an excellent candidate to modify current drugs in treating Alzheimer’s disease (AD).     

Novel tacrine–ebselen hybrids with improved cholinesterase inhibitory,hydrogen peroxide and peroxynitrite scavenging activity

A series of tacrine–ebselen hybrids were synthesised and evaluated as possible multifunctional anti-Alzheimer’s disease (AD) agents. Compound 6i, which is tacrine linked with 5,6-dimethoxybenzo[d][1,2]selenazol-3(2H)-one by a six-carbon spacer, was the most potent acetylcholinesterase (AChE) and butylcholinesterase (BuChE) inhibitor, with IC₅₀ values of 2.55 and 2.80 nM, respectively. Furthermore, this compound demonstrated similar hydrogen peroxide and peroxynitrite scavenging activity as ebselen by horseradish peroxidase assay and peroxynitrite scavenging activity assay, indicating that this hybrid is a good multifunctional drug candidate for the treatment of AD.     

Design,synthesis and neuroprotective evaluation of novel tacrine–benzothiazole hybrids as multi-targeted compounds against Alzheimer’s disease

Alzheimer’s disease (AD) is a multifactorial disorder with several target proteins contributing to its etiology. In search for multifunctional anti-AD drug candidates, taking into account that the acetylcholinesterase (AChE) and beta-amyloid (Aβ) aggregation are particularly important targets for inhibition, the tacrine and benzothiazole (BTA) moieties were conjugated with suitable linkers in a novel series of hybrids. The designed compounds (7a–7e) were synthesized and in vitro as well as in ex vivo evaluated for their capacity for the inhibition of acetylcholinesterase (AChE) and Aβ self-induced aggregation, and also for the protection of neuronal cells death (SHSY-5Y cells, AD and MCI cybrids). All the tacrine–BTA hybrids displayed high in vitro activities, namely with IC₅₀ values in the low micromolar to sub-micromolar concentration range towards the inhibition of AChE, and high percentages of inhibition of the self-induced Aβ aggregation. Among them, compound 7a, with the shortest linker, presented the best inhibitory activity of AChE (IC₅₀ = 0.34 μM), while the highest activity as anti-Aβ₄₂ self-aggregation, was evidenced for compound 7b (61.3%, at 50 μM. The docking studies demonstrated that all compounds are able to interact with both catalytic active site (CAS) and peripheral anionic site (PAS) of AChE. Our results show that compounds 7d and 7e improved cell viability in cells treated with Aβ₄₂ peptide. Overall, these multi-targeted hybrid compounds appear as promising lead compounds for the treatment of Alzheimer’s disease.     

Design,synthesis and evaluation of novel tacrine-(β-carboline) hybrids as multifunctional agents for the treatment of Alzheimer’s disease

A series of tacrine-(β-carboline) hybrids (11a–q) were designed, synthesized and evaluated as multifunctional cholinesterase inhibitors against Alzheimer’s disease (AD). In vitro studies showed that most of them exhibited significant potency to inhibit acetylcholinesterase (eeAChE and hAChE), butyrylcholinesterase (BuChE) and self-induced β-amyloid (Aβ) aggregation, Cu²⁺-induced Aβ (1–42) aggregation, and to chelate metal ions. Especially, 11l presented the greatest ability to inhibit cholinesterase (IC₅₀, 21.6 nM for eeAChE, 63.2 nM for hAChE and 39.8 nM for BuChE), good inhibition of Aβ aggregation (65.8% at 20 μM) and good antioxidant activity (1.57 trolox equivalents). Kinetic and molecular modeling studies indicated that 11l was a mixed-type inhibitor, binding simultaneously to the catalytic anionic site (CAS) and the peripheral anionic site (PAS) of AChE. In addition, 11l could chelate metal ions, reduce PC12 cells death induced by oxidative stress and penetrate the blood–brain barrier (BBB). These results suggested that 11l might be an excellent multifunctional agent for AD treatment.     

Novel pyrazoline amidoxime and their 1,2,4-oxadiazole analogues: Synthesis and pharmacological screening

A novel series of pyrazoline amidoxime (2a–d) and pyrazoly-1,2,4-oxadiazole (3a–p) and (4) of pharmacological significance have been synthesised. Structures of newly synthesised compounds were characterized by spectral studies. New compounds were screened for their in vitro antioxidant, antimicrobial and antiinflammatory activities. Among the synthesized compounds, compound 2a, 3l and 3o were found to be active antimicrobial agents in addition to having potent antioxidant activity, while the compound 3f showed promising antiinflammatory activity in comparison with standard drug.     

Design,synthesis, cholinesterase inhibition and molecular modelling study of novel tacrine hybrids with carbohydrate derivatives

A series of hybrids containing tacrine linked to carbohydrate-based moieties, such as d-xylose, d-ribose, and d-galactose derivatives, were synthesized by the nucleophilic substitution between 9-aminoalkylamino-1,2,3,4-tetrahydroacridines and the corresponding sugar-based tosylates. All compounds were found to be potent inhibitors of both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in the nanomolar IC₅₀ scale. Most of the d-xylose derivatives (6a-e) were selective for AChE and the compound 6e (IC₅₀?=?2.2?nM for AChE and 4.93?nM for BuChE) was the most active compound for both enzymes. The d-galactose derivative 8a was the most selective for AChE exhibiting an IC₅₀ ratio of 7.6 for AChE over BuChE. Only two compounds showed a preference for BuChE, namely 7a (d-ribose derivative) and 6b (d-xylose derivative). Molecular docking studies indicated that the inhibitors are capable of interacting with the entire binding cavity and the main contribution of the linker is to enable the most favorable positioning of the two moieties with CAS, PAS, and hydrophobic pocket to provide optimal interactions with the binding cavity. This finding is reinforced by the fact that there is no linear correlation between the linker size and the observed binding affinities. The majority of the new hybrids synthesized in this work do not violate the Lipinski's rule-of-five according to FAF-Drugs4, and do not demonstrated predicted hepatotoxicity according ProTox-II.     

Design,synthesis and evaluation of 2,4-disubstituted pyrimidines as cholinesterase inhibitors

A group of 2,4-disubstituted pyrimidine derivatives (7a–e, 8a–e and 9a–d) that possess a variety of C-2 aliphatic five- and six-membered heterocycloalkyl ring in conjunction with a C-4 arylalkylamino substituent were designed, synthesized and evaluated as cholinesterase (ChE) inhibitors. The steric and electronic properties at C-2 and C-4 positions of the pyrimidine ring were varied to investigate their effect on ChE inhibitory potency and selectivity. The structure–activity relationship (SAR) studies identified N-benzyl-2-thiomorpholinopyrimidin-4-amine (7c) as the most potent cholinesterase inhibitor (ChEI) with an IC₅₀ = 0.33 μM (acetylcholinesterase, AChE) and 2.30 μM (butyrylcholinesterase, BuChE). The molecular modeling studies indicate that within the AChE active site, the C-2 thiomorpholine substituent was oriented toward the cationic active site region (Trp84 and Phe330) whereas within the BuChE active site, it was oriented toward a hydrophobic region closer to the active site gorge entrance (Ala277). Accordingly, steric and electronic properties at the C-2 position of the pyrimidine ring play a critical role in ChE inhibition.     

Design,synthesis and pharmacological evaluation of novel tacrine–caffeic acid hybrids as multi-targeted compounds against Alzheimer’s disease

A novel series of tacrine–caffeic acid hybrids (5a–f) were designed and synthesized by combining caffeic acid (CA) with tacrine. The antioxidant study revealed that all the hybrids have much more antioxidant capacities compared to CA. Among these compounds, 5e showed the highest selectivity in inhibiting acetylcholinesterase (AChE) over butyrylcholinesterase (BuChE). Enzyme kinetic study had suggested that 5e binds to both catalytic (CAS) and peripheral anionic sites (PAS) of AChE. Moreover, compound 5e also inhibited self- or AChE-induced β-amyloid_1–40 aggregation, as well as had potent neuroprotective effects against H₂O₂- and glutamate- induced cell death with low toxicity in HT22 cells.     

Tacrine–propargylamine derivatives with improved acetylcholinesterase inhibitory activity and lower hepatotoxicity as a potential lead compound for the treatment of Alzheimer’s disease

Abstract

A series of tacrine–propargylamine derivatives were synthesised and evaluated as possible anti-Alzheimer’s disease (AD) agents. Among these derivatives, compounds 3a and 3b exhibited superior activities and a favourable balance of AChE and BuChE activities (3a: IC₅₀ values of 51.3 and 77.6?nM; 3b: IC₅₀ values of 11.2 and 83.5?nM). Compounds 3a and 3b also exhibited increased hAChE inhibitory activity compared with tacrine by approximately 5- and 28-fold, respectively, and low neurotoxicity. Importantly, these compounds also had lower hepatotoxicity than tacrine. Based on these results, compounds 3a and 3b could be considered as potential lead compounds for the treatment of AD and other AChE related diseases, such as schizophrenia, glaucoma and myasthenia gravis.     

Design,synthesis and anti-Alzheimer's disease activity study of xanthone derivatives based on multi-target strategy

A series of xanthone derivatives were designed, synthesized and evaluated as multifunctional ligands against Alzheimer’s disease (AD). In vitro studies showed all xanthone derivatives had good metal chelating property and exhibited selective inhibitory activity against Acetylcholinesterase (AChE). In particular, compound 2a showed the highest inhibitory activity against AChE, and the IC₅₀ value was (0.328 ± 0.001) μM, which was comparable to tacrine. Kinetic analysis and molecular docking studies indicated that these derivatives targeted both the catalytically active site (CAS) and the peripheral anion site (PAS) of AChE. Moreover, all derivatives showed higher anti-oxidative activity than vitamin C. Furthermore, copper complex had higher anti-AChE activity and antioxidant activity. Thus, these xanthone derivatives are potential multi-targeted-directed ligands for further development for the treatment of AD.     

Development of cyanopyridine–triazine hybrids as lead multitarget anti-Alzheimer agents

A series of new cyanopyridine–triazine hybrids were designed, synthesized and screened as multitargeted anti-Alzheimer’s agents. These molecules were designed while using computational techniques and were synthesized via a feasible concurrent synthetic route. Inhibition potencies of synthetic compounds 4a–4h against cholinesterases, Aβ_1–42 disaggregation, oxidative stress, cytotoxicity, and neuroprotection against Aβ_1–42-induced toxicity of the synthesized compounds were evaluated. Compounds 4d and 4h showed promising inhibitory activity on acetylcholinesterase (AChE) with IC₅₀ values 0.059 and 0.080 μM, respectively, along with good inhibition selectivity against AChE over butyrylcholinesterase (BuChE). Molecular modelling studies revealed that these compounds interacted simultaneously with the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE. The mixed type inhibition of compound 4d further confirmed their dual binding nature in kinetic studies. Furthermore, the results from neuroprotection studies of most potent compounds 4d and 4h indicate that these derivatives can reduce neuronal death induced by H₂O₂-mediated oxidative stress and Aβ_1–42 induced cytotoxicity. In addition, in silico analysis of absorption, distribution, metabolism and excretion (ADME) profile of best compounds 4d and 4h revealed that they have drug like properties. Overall, these cyanopyridine–triazine hybrids can be considered as a candidate with potential impact for further pharmacological development in Alzheimer’s therapy.     

Synthesis and in vitro evaluation of vanillin derivatives as multi-target therapeutics for the treatment of Alzheimer’s disease

A number of novel naphthalimido and phthalimido vanillin derivatives were synthesised, and evaluated as antioxidants and cholinesterase inhibitors in vitro. Antioxidant activity was assessed using DPPH, FRAP, and ORAC assays. All compounds demonstrated enhanced activity compared to the parent compound, vanillin. They also exhibited BuChE selectivity in Ellman’s assay. A lead compound, 2a (2-(3-(bis(4-hydroxy-3-methoxybenzyl)amino)propyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione), was identified and displayed strong antioxidant activity (IC₅₀ of 16.67 µM in the DPPH assay, a 25-fold increase in activity compared to vanillin in the FRAP assay, and 9.43 TE in the ORAC assay). Furthermore, 2a exhibited potent BuChE selectivity, with an IC₅₀ of 0.27 µM which was around 53-fold greater than the corresponding AChE inhibitory activity. Molecular modelling studies showed that molecules with bulkier groups, as in 2a, exhibited better BuChE selectivity. This work provides a promising basis for the development of multi-target hybrid compounds based on vanillin as potential AD therapeutics.     

Novel multipotent phenylthiazole–tacrine hybrids for the inhibition of cholinesterase activity, β-amyloid aggregation and Ca2+ overload

In this study, a series of multipotent phenylthiazole–tacrine hybrids (7a–7e, 8, and 9a–9m) were synthesized and biologically evaluated. Screening results showed that phenylthiazole–tacrine hybrids were potent cholinesterase inhibitors with pIC₅₀ (?log IC₅₀) value ranging from 5.78 ± 0.05 to 7.14 ± 0.01 for acetylcholinesterase (AChE), and from 5.75 ± 0.03 to 10.35 ± 0.15 for butyrylcholinesterase (BuChE). The second series of phenylthiazole–tacrine hybrids (9a–9m) could efficiently prevent Aβ_1–42 self-aggregation. The structure–activity relationship revealed that their inhibitory potency relied on the type of middle linker and substitutions at 4′-position of 4-phenyl-2-aminothiazole. In addition, 7a and 7c also displayed the Ca²⁺ overload blockade effect in the primary cultured cortical neurons. Consequently, these compounds emerged as promising molecules for the therapy of Alzheimer’s disease.     

Novel 3-substituted-1-aryl-5-phenyl-6-anilinopyrazolo[3,4-d]pyrimidin-4-ones: Docking,synthesis and pharmacological evaluation as a potential anti-inflammatory agents

Novel 3-substituted-1-aryl-5-phenyl-6-anilino-pyrazolo[3,4-d]pyrimidin-4-ones of pharmacological significance were synthesized by the reaction of ethyl-(5-amino-3-methylthio-1-aryl-5-phenyl-2H-pyrazole)-4-carboxylates 3a–c with S-methyl diphenyl thiourea independently to produce 1-aryl-3-thiomethyl-5-phenyl-pyrazolo[3,4-d]pyrimidines 4a–c in DMF with catalytic amount of K₂CO₃, which on further treatment with different aromatic amines independently under same reaction conditions generated for compounds 5a–l. The compounds were screened for the anti-inflammatory activity and evaluated for ulcerogenic potential. The compounds 5i exhibited superior anti-inflammatory activity in comparison with diclofenac sodium and comparable activity with celecoxib at a dose of 25 mg/kg. The other compounds 4c, 5c, 5f and 5l were found as active with inhibition of edema in the range of 35–39 after 3 h of administration of test compounds. The ulcerogenic potential of active compounds was observed to be quite lesser as compared to standard. COX-2 docking score of the active compound 5i was found to be better than standard celecoxib.     

Synthesis,biological evaluation and molecular modeling of substituted 2-aminobenzimidazoles as novel inhibitors of acetylcholinesterase and butyrylcholinesterase

A series of novel 2-aminobenzimidazole derivatives were synthesized under microwave irradiation. Their biological activities were evaluated on acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). A number of the 2-aminobenzimidazole derivatives showed good inhibitory activities to AChE and BuChE. Among them, compounds 9, 12 and 13 were found to be >25-fold more selective for BuChE than AChE. No evidence of cytotoxicity was observed by MTT assay in PC12 cells or HepG2 cells exposed to 100 μM of the compounds. Molecular modeling studies indicate that the benzimidazole moiety of compounds 9, 12 and 13 forms a face-to-face π–π stacking interaction in a ‘sandwich’ form with the indole ring of Trp82 (4.09 Å) in the active gorge, and compounds 12 and 13 form a hydrogen bond with His438 at the catalytic site of BuChE. In addition, compounds 12 and 13 fit well into the hydrophobic pocket formed by Ala328, Trp430 and Tyr332 of BuChE. Our data suggest the 2-aminobenzimidazole drugs as promising new selective inhibitors for AChE and BuChE, potentially useful to treat neurodegenerative diseases.     

Synthesis,bioactivity and molecular modeling studies on potential anti-Alzheimer piperidinehydrazide-hydrazones

A group of N-benzylpiperidine-3/4-carbohydrazide-hydrazones were designed, synthesized and evaluated for acetylcholinesterase (AChE), butyrylcholinesterase (BuChE) activities, Aβ₄₂ self-aggregation inhibitory potentials, and antioxidant capacities, in vitro. All of the compounds displayed eeAChE and huAChE inhibitory activity in a range of IC₅₀ = 5.68–11.35 µM and IC₅₀ = 8.80–74.40 µM, respectively and most of the compounds exhibited good to moderate inhibitory activity on BuChE enzyme. Kinetic analysis and molecular modeling studies were also performed for the most potent compounds (1g and 1j). Not only the molecular modeling studies but also the kinetic analysis suggested that these compounds might be able to interact with the catalytic active site (CAS) and the peripheral anionic site (PAS) of the enzymes. In the light of the results, compound 1g and compound 1j may be suggested as lead compounds for multifunctional therapy of AD.     

Highly potent and selective aryl-1,2,3-triazolyl benzylpiperidine inhibitors toward butyrylcholinesterase in Alzheimer's disease

Acetylcholinesterase (AChE) is the key enzyme targeted in Alzheimer's disease (AD) therapy, nevertheless butyrylcholinesterase (BuChE) has been drawing attention due to its role in the disease progression. Thus, we aimed to synthesize novel cholinesterases inhibitors considering structural differences in their peripheral site, exploiting a moiety replacement approach based on the potent and selective hAChE drug donepezil. Hence, two small series of N-benzylpiperidine based compounds have successfully been synthesized as novel potent and selective hBuChE inhibitors. The most promising compounds (9 and 11) were not cytotoxic and their kinetic study accounted for dual binding site mode of interaction, which is in agreement with further docking and molecular dynamics studies. Therefore, this study demonstrates how our strategy enabled the discovery of novel promising and privileged structures. Remarkably, compound 11 proved to be one of the most potent (0.17?nM) and selective (>58,000-fold) hBuChE inhibitor ever reported.     

Synthesis and biological evaluation of novel quinazoline-triazole hybrid compounds with potential use in Alzheimer’s disease

A library of twelve quinazoline-triazole hybrid compounds were designed, synthesized and evaluated as a novel class of acetylcholinesterase inhibitors to treat Alzheimer’s disease (AD). The biological assay results demonstrated the ability of several hybrid compounds to inhibit AChE enzyme (IC₅₀ range = 0.2–83.9 µM). To understand the high potential activity of these compounds, molecular docking simulations were performed to get better insights into the mechanism of binding of quinazoline-triazole hybrid compounds. As expected, compounds 8a and 9a-b bind to both catalytic anionic site (CAS) and peripheral anionic site (PAS) in the active site of AChE enzyme, which implicates that these compounds could act as dual binding site inhibitors. These compounds were not cytotoxic and they also displayed appropriated physicochemical as well as pharmacokinetic profile to be developed as novel anti-AD drug candidates.     

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.