Syntheses of coumarin–tacrine hybrids as dual-site acetylcholinesterase inhibitors and their activity against butylcholinesterase,Aβ aggregation,and β-secretase

Exploring small-molecule acetylcholinesterase (AChE) inhibitors to slow the breakdown of acetylcholine (Ach) represents the mainstream direction for Alzheimer’s disease (AD) therapy. As the first acetylcholinesterase inhibitor approved for the clinical treatment of AD, tacrine has been widely used as a pharmacophore to design hybrid compounds in order to combine its potent AChE inhibition with other multi-target profiles. In present study, a series of novel tacrine–coumarin hybrids were designed, synthesized and evaluated as potent dual-site AChE inhibitors. Moreover, compound 1g was identified as the most potent candidate with about 2-fold higher potency (K_i = 16.7 nM) against human AChE and about 2-fold lower potency (K_i = 16.1 nM) against BChE than tacrine (K_i = 35.7 nM for AChE, K_i = 8.7 nM for BChE), respectively. In addition, some of the tacrine–coumarin hybrids showed simultaneous inhibitory effects against both Aβ aggregation and β-secretase. We therefore conclude that tacrine–coumarin hybrid is an interesting multifunctional lead for the AD drug discovery.     

Design,synthesis and biological evaluation of novel N-phosphorylated and O-phosphorylated tacrine derivatives as potential drugs against Alzheimer’s disease

In this work, we designed, synthesised and biologically investigated a novel series of 14 N- and O-phosphorylated tacrine derivatives as potential anti-Alzheimer’s disease agents. In the reaction of 9-chlorotacrine and corresponding diamines/aminoalkylalcohol we obtained diamino and aminoalkylhydroxy tacrine derivatives. Next, the compounds were acid to give final products 6–13 and 16–21 that were characterised by ¹H, ¹³C, ³¹P NMR and MS. The results of the docking studies revealed that the designed phosphorus hybrids, in theory can bind to AChE and BChE. All compounds exhibited significantly lower AutoDock Vina scores compared to tacrine. The inhibitory potency evaluation was performed using the Ellman’s method. The most inhibitory activity against AChE exhibited compound 8 with an IC₅₀ value of 6.11 nM and against BChE 13 with an IC₅₀ value of 1.97 nM and they were 6- and 12-fold potent than tacrine. Compound 19 showed the lack of hepatocytotoxicity in MTT assay.     

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 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.     

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.     

Donepezil-tacrine hybrid related derivatives as new dual binding site inhibitors of AChE

A new series of donepezil–tacrine hybrid related derivatives have been synthesised as dual acetylcholinesterase inhibitors that could bind simultaneously to the peripheral and catalytic sites of the enzyme. These new hybrids combined a tacrine, 6-chlorotacrine or acridine unit as catalytic binding site and indanone (the heterocycle present in donepezil) or phthalimide moiety as peripheral binding site of the enzyme, connected through a different linker tether length. One of the synthesised compounds emerged as a potent and selective AChE inhibitor, which is able to displace propidium in a competition assay. These results seem to confirm the ability of this inhibitor to bind simultaneously to both sites of the enzyme and make it a promising lead for developing disease-modifying drugs for the future treatment of Alzheimer’s disease. To gain insight into the molecular determinants that modulate the inhibitory activity of these compounds, a molecular modelling study was performed to explore their binding to the enzyme.     

Dual functional cholinesterase and PDE4D inhibitors for the treatment of Alzheimer’s disease: Design,synthesis and evaluation of tacrine-pyrazolo[3,4-b]pyridine hybrids

A series of tacrine-pyrazolo[3,4-b]pyridine hybrids were synthesised and evaluated as dual cholinesterase (ChE) and phosphodiesterase 4D (PDE4D) inhibitors for the treatment of Alzheimer’s disease (AD). Compound 10j, which is tacrine linked with pyrazolo[3,4-b]pyridine moiety by a six-carbon spacer, was the most potent acetylcholinesterase (AChE) with IC₅₀ value of 0.125 μM. Moreover, compound 10j provided a desired balance of AChE and butylcholinesterase (BuChE) and PDE4D inhibition activities, with IC₅₀ value of 0.449 and 0.271 μM, respectively. The above results indicated that this hybrid was a promising dual functional agent for the treatment of AD.     

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).     

Inhibition of cholinesterase and monoamine oxidase-B activity by Tacrine–Homoisoflavonoid hybrids

A series of Tacrine–Homoisoflavonoid hybrids were designed, synthesised and evaluated as inhibitors of cholinesterases (ChEs) and human monoamine oxidases (MAOs). Most of the compounds were found to be potent against both ChEs and MAO-B. Among these hybrids, compound 8b, with a 6 carbon linker between tacrine and (E)-7-hydroxy-3-(4-methoxybenzylidene)chroman-4-one, proved to be the most potent against AChE and MAO-B with IC₅₀ values of 67.9 nM and 0.401 μM, respectively. This compound was observed to cross the blood–brain barrier (BBB) in a parallel artificial membrane permeation assay for the BBB (PAMPA-BBB). The results indicated that compound 8b is an excellent multifunctional promising compound for development of novel drugs for Alzheimer’s disease (AD).     

Synthesis and in vitro evaluation of N-alkyl-7-methoxytacrine hydrochlorides as potential cholinesterase inhibitors in Alzheimer disease

All approved drugs for Alzheimer disease (AD) in clinical practice ameliorate the symptoms of the disease. Among them, acetylcholinesterase inhibitors (AChEIs) are used to increase the cholinergic activity. Among new AChEI, tacrine compounds were found to be more toxic compared to 7-MEOTA (9-amino-7-methoxy-1,2,3,4-tetrahydroacridine). In this Letter, series of 7-MEOTA analogues (N-alkyl-7-methoxytacrine) were synthesized. Their inhibitory ability was evaluated on recombinant human acetylcholinesterase (AChE) and plasmatic human butyrylcholinesterase (BChE). Three novel compounds showed promising results towards hAChE better to THA or 7-MEOTA. Three compounds resulted as potent inhibitors of hBChE. The SAR findings highlighted the C₆–C₇ N-alkyl chains for cholinesterase inhibition.     

Inhibition of cholinesterase activity and amyloid aggregation by berberine-phenyl-benzoheterocyclic and tacrine-phenyl-benzoheterocyclic hybrids

A series of berberine-phenyl-benzoheterocyclic (26-29) and tacrine-phenyl-benzoheterocyclic hybrids (44-46) were synthesised and evaluated as multifunctional anti-Alzheimer's disease agents. Compound 44b, tacrine linked with phenyl-benzothiazole by 3-carbon spacers, was the most potent AChE inhibitor with an IC(50) value of 0.017 μM. This compound demonstrated similar Aβ aggregation inhibitory activity with cucurmin (51.8% vs 52.1% at 20 μM, respectively), indicating that this hybrid is an excellent multifunctional drug candidate for AD.     

O-Hydroxyl- or o-amino benzylamine-tacrine hybrids: Multifunctional biometals chelators,antioxidants, and inhibitors of cholinesterase activity and amyloid-β aggregation

In an effort to identify novel multifunctional drug candidates for the treatment of Alzheimer’s disease (AD), a series of hybrid molecules were synthesised by reacting N-(aminoalkyl)tacrine with salicylic aldehyde or derivatives of 2-aminobenzaldehyde. These compounds were then evaluated as multifunctional anti-Alzheimer’s disease agents. All of the hybrids are potential biometal chelators, and in addition, most of them were better antioxidants and inhibitors of cholinesterases and amyloid-β (Aβ) aggregation than the lead compound tacrine. Compound 7c has the potential to be a candidate for AD therapy: it is a much better inhibitor of acetylcholinesterase (AChE) than tacrine (IC₅₀: 0.55 nM vs 109 nM), has good biometal chelation ability, is able to inhibit Aβ aggregation and has moderate antioxidant activity (1.22 Trolox equivalents).     

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.     

Novel tacrine–benzofuran hybrids as potential multi-target drug candidates for the treatment of Alzheimer’s Disease

Abstract

Pursuing the widespread interest on multi-target drugs to combat Alzheimer´s disease (AD), a new series of hybrids was designed and developed based on the repositioning of the well-known acetylcholinesterase (AChE) inhibitor, tacrine (TAC), by its coupling to benzofuran (BF) derivatives. The BF framework aims to endow the conjugate molecules with ability for inhibition of AChE (bimodal way) and of amyloid-beta peptide aggregation, besides providing metal (Fe, Cu) chelating ability and concomitant extra anti-oxidant activity, for the hybrids with hydroxyl substitution. The new TAC-BF conjugates showed very good activity for AChE inhibition (sub-micromolar range) and good capacity for the inhibition of self- and Cu-mediated Aβ aggregation, with dependence on the linker size and substituent groups of each main moiety. Neuroprotective effects were also found for the compounds through viability assays of neuroblastoma cells, after Aβ_1-42 induced toxicity. Structure-activity relationship analysis provides insights on the best structural parameters, to take in consideration for future studies in view of potential applications in AD therapy.     

Molecular-docking-guided design and synthesis of new IAA-tacrine hybrids as multifunctional AChE/BChE inhibitors

A series of new indole-3-acetic acid (IAA)-tacrine hybrids as dual acetylcholinesterase (AChE)/butyrylcholinesterase (BChE) inhibitors were designed and prepared based on the molecular docking mode of AChE with an IAA derivative (1a), a moderate AChE inhibitor identified by screening our compound library for anti-Alzheimer’s disease (AD) drug leads. The enzyme assay results revealed that some hybrids, e.g. 5d and 5e, displayed potent dual in vitro inhibitory activities against AChE/BChE with IC₅₀ values in low nanomolar range. Molecular modeling studies in tandem with kinetic analysis suggest that these hybrids target both catalytic active site and peripheral anionic site of cholinesterase (ChE). Molecular dynamic simulations and Molecular Mechanics/Poisson-Boltzmann Surface Area (MM-PBSA) calculations indicate that 5e has more potent binding affinity than hit 1a, which may explain the stronger inhibitory effect of 5e on AChE. Furthermore, their predicted pharmacokinetic properties and in vitro influences on mouse brain neural network electrical activity were discussed. Taken together, compound 5e can be highlighted as a lead compound worthy of further optimization for designing new anti-AD drugs.     

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.     

Novel chromanone-dithiocarbamate hybrids as multifunctional AChE inhibitors with β-amyloid anti-aggregation properties for the treatment of Alzheimer’s disease

By connecting chromanone with dithiocarbamate moieties through flexible linkers, a series of hybrids as novel multifunctional AChE inhibitors have been designed and synthesized. Most of these compounds displayed strong and excellently selective inhibition to eeAChE as well as potent inhibition to self- and AChE-induced Aβ aggregation. Among them, compound 6c showed the best activity to inhibit eeAChE (IC₅₀ = 0.10 μM) and AChE-induced Aβ aggregation (33.02% at 100 μM), and could effectively inhibit self-induced Aβ aggregation (38.25% at 25 μM). Kinetic analysis and docking study indicated that compound 6c could target both the CAS and PAS, suggesting that it was a dual binding site inhibitor for AChE. Besides, it exhibited good ability to penetrate the BBB and low neurotoxicity in SH-SY5Y cells. More importantly, compound 6c was well tolerated in mice (2500 mg/kg, po) and could attenuate the memory impairment in a scopolamine-induced mouse model. Overall, these results highlight 6c as a promising multifunctional agent for treating AD and also demonstrate that the dithiocarbamate is a valid scaffold for design of multifunctional AChE inhibitors.     

Inhibitory effect of ursolic acid purified from Origanum majorana L on the acetylcholinesterase

We screened 139 herbal spices in search of the acetylcholinesterase (AChE) inhibitor from natural resources. AChE inhibitors, which enhance cholinergic transmission by reducing the enzymatic degradation of acetylcholine, are the only source of compound currently approved for the treatment of Alzheimer's Disease (AD). Among these herbs, edible plants and spices, the ethanol extract from Origanum majorana L. showed the highest inhibitory effect on AChE in vitro. By sequential fractionation of Origanum majorana L. the active component was finally identified as ursolic acid (3 beta-Hydroxyurs-12-en-28-oic acid). The ursolic acid of Origanum majorana L. inhibited AChE activity in a dose-dependent and competitive/non-competitive type. The Ki value (representing the affinity of the enzyme and inhibitor) of Origanum majorana L. ursolic acid was 6 pM, and that of tacrine was 0.4 nM. The concentration required for 50% enzyme inhibition of the active component (IC50 value) was 7.5 nM, and that of tacrine was 1 nM. This study demonstrated that the ursolic acid of Origanum majorana L. appeared to be a potent AChE inhibitor in Alzheimer's Disease.     

Novel tacrine-coumarin hybrids linked to 1,2,3-triazole as anti-Alzheimer’s compounds: In vitro and in vivo biological evaluation and docking study

A new series of tacrine-coumarin hybrids linked to 1,2,3-triazole were designed, synthesized, and tested as potent dual binding site cholinesterase inhibitors (ChEIs) for the treatment of Alzheimer’s disease (AD). Among them, compound 8e was the most potent anti-AChE derivative (IC₅₀ = 27 nM) and compound 8m displayed the best anti-BChE activity (IC₅₀ = 6 nM) much more active than tacrine and donepezil as the reference drugs. Compound 8e was also evaluated for its BACE1 inhibitory activity and neuroprotectivity against PC12 cells exposed to Aβ_25-35 which indicated low activity. Finally, in vivo studies by Morris water maze task showed that compound 8e significantly reversed scopolamine-induced memory deficit in rats.     

New performance of biosensor technology for Alzheimer's disease drugs: in vitro comparison of tacrine and 7-methoxytacrine

Two drugs were tested using electrochemical biosensor with immobilized acetylcholinesterase (AChE). The first was commercialized drug tacrine (known also as Cognex) used for treatment of cognitive manifestation of Alzheimer\'s disease (AD). The second one was its 7-methoxy derivate (7-MEOTA) that has not been marketed. We determined the IC50 (6.67+/-0.92)x10-7 M for tacrine and (1.66+/-1.43)x10-9 M for 7-MEOTA. In this in vitro study, 7-MEOTA acts as stronger inhibitor of AChE and in this way could be more favorable for treatment of cognitive manifestation of AD. Our study shows that biosensor technology could be used as a quick and cheap tool for testing of promising AChE inhibitors (AD drug candidates).