Design, Synthesis, and Biological Evaluation of Novel Tetrahydroacridin Hybrids with Sulfur-Inserted Linkers as Potential Multitarget Agents for Alzheimer's Disease.

Alzheimer's disease (AD) is a complex neurodegenerative disease that can lead to the loss of cognitive function. The progression of AD is regulated by multiple signaling pathways and their associated targets. Therefore, multitarget strategies theoretically have greater potential for treating AD. In this work, a series of new hybrids were designed and synthesized by the hybridization of tacrine (4, AChE: IC50 = 0.223 µM) with pyrimidone compound 5 (GSK-3ß: IC50 = 3 µM) using the cysteamine or cystamine group as the connector. The biological evaluation results demonstrated that most of the compounds exhibited moderate to good inhibitory activities against acetylcholinesterase (AChE) and glycogen synthase kinase 3ß (GSK-3ß). The optimal compound 18a possessed potent dual AChE/GSK-3ß inhibition (AChE: IC50 = 0.047 ± 0.002 µM, GSK-3ß: IC50 = 0.930 ± 0.080 µM). Further molecular docking and enzymatic kinetic studies revealed that this compound could occupy both the catalytic anionic site and the peripheral anionic site of AChE. The results also showed a lack of toxicity to SH-SY5Y neuroblastoma cells at concentrations of up to 25 µM. Collectively, this work explored the structure-activity relationships of novel tetrahydroacridin hybrids with sulfur-inserted linkers, providing a reference for the further research and development of new multitarget anti-AD drugs.

Novel diarylated tacrine derivatives: Synthesis, characterization, anticancer, antiepileptic, antibacterial, and antifungal activities.

In this study, our goal was to synthesize novel aryl tacrine derivatives and assess their potential as anticancer, antibacterial agents, and enzyme inhibitors. We adopted a two-step approach, initiating with the synthesis of dibromotacrine derivatives 3 and 4 through the Friedlander reaction. These intermediates underwent further transformation into diarylated tacrine derivatives 3a-e and 4a-e using a Suzuki-Miyaura cross-coupling reaction. Thorough characterization of these novel diarylated tacrines was achieved using various spectroscopic techniques. Our findings highlighted the potent anticancer effects of these innovative compounds across a range of cancer cell lines, including lung, gynecologic, bone, colon, and breast cancers, while demonstrating low cytotoxicity against normal cells. Notably, these compounds surpassed the control drug, 5-Fluorouracil, in terms of antiproliferative activity in numerous cancer cell lines. Moreover, our investigation included an analysis of the inhibitory properties of these novel compounds against various microorganisms and cytosolic carbonic anhydrase enzymes. The results suggest their potential for further exploration as cancer-specific, enzyme inhibitory, and antibacterial therapeutic agents. Notably, four compounds, namely, 5,7-bis(4-(methylthio)phenyl)tacrine (3d), 5,7-bis(4-(trifluoromethoxy)phenyl)tacrine (3e), 2,4-bis(4-(trifluoromethoxy)phenyl)-7,8,9,10-tetrahydro-6H-cyclohepta[b]quinolin-11-amine (4e), and 6,8-dibromotacrine (3), emerged as the most promising candidates for preclinical studies.

Quinolinetrione-tacrine hybrids as multi-target-directed ligands against Alzheimer's disease.

Multi-target drug discovery is one of the most active fields in the search for new drugs against Alzheimer's disease (AD). This is because the complexity of AD pathological network might be adequately tackled by multi-target-directed ligands (MTDLs) aimed at modulating simultaneously multiple targets of such a network. In a continuation of our efforts to develop MTDLs for AD, we have been focusing on the molecular hybridization of the acetylcholinesterase inhibitor tacrine with the aim of expanding its anti-AD profile. Herein, we manipulated the structure of a previously developed tacrine-quinone hybrid (1). We designed and synthesized a novel set of MTDLs (2-6) by replacing the naphthoquinone scaffold of 1 with that of 2,5,8-quinolinetrione. The most interesting hybrid 3 inhibited cholinesterase enzymes at nanomolar concentrations. In addition, 3 exerted antioxidant effects in menadione-induced oxidative stress of SH-SY5Y cells. Importantly, 3 also showed low hepatotoxicity and good anti-amyloid aggregation properties. Remarkably, we uncovered the potential of the quinolinetrione scaffold, as a novel anti-amyloid aggregation and antioxidant motif to be used in further anti-AD MTDL drug discovery endeavors.

Chromone Containing Hybrid Analogs: Synthesis and Applications in Medicinal Chemistry.

The use of privileged scaffolds has proven beneficial for generating novel bioactive scaffolds in drug discovery program. Chromone is one such privileged scaffold that has been exploited for designing pharmacologically active analogs. The molecular hybridization technique combines the pharmacophoric features of two or more bioactive compounds to avail a better pharmacological activity in the resultant hybrid analogs. The current review summarizes the rationale and techniques involved in developing hybrid analogs of chromone, which show potential in fields of obesity, diabetes, cancer, Alzheimer's disease and microbial infections. Here the molecular hybrids of chromone with various pharmacologically active analogs or fragments (donepezil, tacrine, pyrimidines, azoles, furanchalcones, hydrazones, quinolines, etc.) are discussed with their structure-activity relationship against above-mentioned diseases. Detailed methodologies for the synthesis of corresponding hybrid analogs have also been described, with suitable synthetic schemes. The current review will shed light on various strategies utilized for the design of hybrid analogs in the field of drug discovery. The importance of hybrid analogs in various disease conditions is also illustrated.

Novel Dual AChE and ROCK2 Inhibitor Induces Neurogenesis via PTEN/AKT Pathway in Alzheimer's Disease Model.

Alzheimer's disease (AD) is a progressive and complex neurodegenerative disease. Acetylcholinesterase inhibitors (AChEIs) are a major class of drugs used in AD therapy. ROCK2, another promising target for AD, has been associated with the induction of neurogenesis via PTEN/AKT. This study aimed to characterize the therapeutic potential of a novel donepezil-tacrine hybrid compound (TA8Amino) to inhibit AChE and ROCK2 protein, leading to the induction of neurogenesis in SH-SY5Y cells. Experiments were carried out with undifferentiated and neuron-differentiated SH-SY5Y cells submitted to treatments with AChEIs (TA8Amino, donepezil, and tacrine) for 24 h or 7 days. TA8Amino was capable of inhibiting AChE at non-cytotoxic concentrations after 24 h. Following neuronal differentiation for 7 days, TA8Amino and donepezil increased the percentage of neurodifferentiated cells and the length of neurites, as confirmed by ß-III-tubulin and MAP2 protein expression. TA8Amino was found to participate in the activation of PTEN/AKT signaling. In silico analysis showed that TA8Amino can stably bind to the active site of ROCK2, and in vitro experiments in SH-SY5Y cells demonstrate that TA8Amino significantly reduced the expression of ROCK2 protein, contrasting with donepezil and tacrine. Therefore, these results provide important information on the mechanism underlying the action of TA8Amino with regard to multi-target activities.

In silico study of tacrine and acetylcholine binding profile with human acetylcholinesterase: docking and electronic structure.

Alzheimer disease (AD) is a neurodegenerative process, one of the most common and incident dementia in the population over 60 years. AD manifests the presence of complex biochemical processes involved in neuronal degeneration, such as the formation of senile plaques containing amyloid-ß peptides, the development of intracellular neurofibrillary tangles, and the suppression of the acetylcholine neurotransmitter. In this way, we performed a set of theoretical tests of tacrine ligand and acetylcholine neurotransmitter against the human acetylcholinesterase enzyme. Molecular docking was used to understand the most important interactions of these molecules with the enzyme. Computational chemistry calculation was carried out using MP2, DFT, and semi-empirical methods, starting from molecular docking structures. We have also performed studies regarding the non-covalent interactions, electron localization function, molecular electrostatic potential and explicit water molecule influence. For Trp86 residue, we show two main interactions in accordance to the results of the literature for TcAChE. First, intermolecular interactions of the cation-π and sigma-π type were found. Second, close stacking interactions were stablished between THA+ and Trp86 residue on one side and with Tyr337 residue on the other side.

Discovery of novel tacrine derivatives as potent antiproliferative agents with CDKs inhibitory property.

Tacrine was the first approved drug by the FDA for the treatment of Alzheimer's disease (AD) but was withdrawn from the market due to its dose-dependent hepatotoxicity. Herein, we describe our efforts toward the discovery of a novel series of tacrine derivatives for cancer therapeutics. Intensive structural modifications of tacrine led to the identification of N-(4-{9-[(3S)-3-aminopyrrolidin-1-yl]-5,6,7,8-tetrahydroacridin-2-yl}pyridin-2-yl)cyclopropanecarboxamide hydrochloride ((S)-45, ZLWT-37) as a potent antiproliferative agent (GI50 = 0.029 µM for HCT116). In addition, ZLWT-37 exhibited lower inhibitory activity against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) compared to tacrine. The in vitro studies demonstrated that ZLWT-37 could significantly induce apoptosis and arrest the cell cycle in the G2/M phase in HCT116 cells. The in vivo studies revealed that compound ZLWT-37 showed excellent antitumor efficacy in HCT116 xenograft tumor model and favorable pharmacokinetics profiles (F% = 28.70%) as well as low toxicity in the acute toxicity test with a median lethal dose (LD50) of 380.3 mg/kg. Encouragingly, ZLWT-37 had no obvious hepatotoxicity, nephrotoxicity, and hematologic toxicity. Kinase assay suggested that ZLWT-37 possessed potent cyclin-dependent kinase 9 (CDK9) inhibitory activity (IC50 = 0.002 µM) and good selectivity over CDK2 (IC50 = 0.054 µM). Collectively, these findings indicate that compound ZLWT-37 is a promising anti-cancer agent that deserves further preclinical evaluation.

Synthesis and evaluation of novel arylisoxazoles linked to tacrine moiety: in vitro and in vivo biological activities against Alzheimer's disease.

Alzheimer's disease (AD) is now ranked as the third leading cause of death after heart disease and cancer. There is no definite cure for AD due to the multi-factorial nature of the disease, hence, multi-target-directed ligands (MTDLs) have attracted lots of attention. In this work, focusing on the efficient cholinesterase inhibitory activity of tacrine, design and synthesis of novel arylisoxazole-tacrine analogues was developed. In vitro acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibition assay confirmed high potency of the title compounds. Among them, compounds 7l and 7b demonstrated high activity toward AChE and BChE with IC50 values of 0.050 and 0.039 µM, respectively. Both compounds showed very good self-induced Aß aggregation and AChE-induced inhibitory activity (79.4 and 71.4% for compound 7l and 61.8 and 58.6% for compound 7b, respectively). Also, 7l showed good anti-BACE1 activity with IC50 value of 1.65 µM. The metal chelation test indicated the ability of compounds 7l and 7b to chelate biometals (Zn2+, Cu2+, and Fe2+). However, they showed no significant neuroprotectivity against Aß-induced damage in PC12 cells. Evaluation of in vitro hepatotoxicity revealed comparable toxicity of compounds 7l and 7b with tacrine. In vivo studies by Morris water maze (MWM) task demonstrated that compound 7l significantly reversed scopolamine-induced memory deficit in rats. Finally, molecular docking studies of compounds 7l and 7b confirmed establishment of desired interactions with the AChE, BChE, and BACE1 active sites.

Design, Synthesis, biological investigations and molecular interactions of triazole linked tacrine glycoconjugates as Acetylcholinesterase inhibitors with reduced hepatotoxicity.

Tacrine is a known Acetylcholinesterase (AChE) inhibitors having hepatotoxicity as main liability associated with it. The present study aims to reduce its hepatotoxicity by synthesizing tacrine linked triazole glycoconjugates via Huisgen's [3 + 2] cycloaddition of anomeric azides and terminal acetylenes derived from tacrine. A series of triazole based glycoconjugates containing both acetylated (A-1 to A-7) and free sugar hydroxyl groups (A-8 to A-14) at the amino position of tacrine were synthesized in good yield taking aid from molecular docking studies and evaluated for their in vitro AChE inhibition activity as well as hepatotoxicity. All the hybrids were found to be non-toxic on HePG2 cell line at 200 µM (100 % cell viability) as compared to tacrine (35 % cell viability) after 24 h of incubation period. Enzyme kinetic studies carried out for one of the potent hybrids in the series A-1 (IC50 0.4 µM) revealed its mixed inhibition approach. Thus, compound A-1 can be used as principle template to further explore the mechanism of action of different targets involved in Alzheimer's disease (AD) which stands as an adequate chemical probe to be launched in an AD drug discovery program.

Tacrine Induces Endoplasmic Reticulum-Stressed Apoptosis via Disrupting the Proper Assembly of Oligomeric Acetylcholinesterase in Cultured Neuronal Cells.

Acetylcholinesterase inhibitors (AChEIs), the most developed treatment strategies for Alzheimer's disease (AD), will be used in clinic for, at least, the next decades. Their side effects are in highly variable from drug to drug with mechanisms remaining to be fully established. The withdrawal of tacrine (Cognex) in the market makes it as an interesting case study. Here, we found tacrine could disrupt the proper trafficking of proline-rich membrane anchor-linked tetrameric acetylcholinesterase (AChE) in the endoplasmic reticulum (ER). The exposure of tacrine in cells expressing AChE, e.g., neurons, caused an accumulation of the misfolded AChE in the ER. This misfolded enzyme was not able to transport to the Golgi/plasma membrane, which subsequently induced ER stress and its downstream signaling cascade of unfolded protein response. Once the stress was overwhelming, the cooperation of ER with mitochondria increased the loss of mitochondrial membrane potential. Eventually, the tacrine-exposed cells lost homeostasis and underwent apoptosis. The ER stress and apoptosis, induced by tacrine, were proportional to the amount of AChE. Other AChEIs (rivastigmine, bis(3)-cognitin, daurisoline, and dauricine) could cause the same problem as tacrine by inducing ER stress in neuronal cells. The results provide guidance for the drug design and discovery of AChEIs for AD treatment. SIGNIFICANCE STATEMENT: Acetylcholinesterase inhibitors (AChEIs) are the most developed treatment strategies for Alzheimer's disease (AD) and will be used in clinic for at least the next decades. This study reports that tacrine and other AChEIs disrupt the proper trafficking of acetylcholinesterase in the endoplasmic reticulum. Eventually, the apoptosis of neurons and other cells are induced. The results provide guidance for drug design and discovery of AChEIs for AD treatment.

Discovery of Novel Tacrine-Pyrimidone Hybrids as Potent Dual AChE/GSK-3 Inhibitors for the Treatment of Alzheimer's Disease.

Based on a multitarget strategy, a series of novel tacrine-pyrimidone hybrids were identified for the potential treatment of Alzheimer's disease (AD). Biological evaluation results demonstrated that these hybrids exhibited significant inhibitory activities toward acetylcholinesterase (AChE) and glycogen synthase kinase 3 (GSK-3). The optimal compound 27g possessed excellent dual AChE/GSK-3 inhibition both in terms of potency and equilibrium (AChE: IC50 = 51.1 nM; GSK-3ß: IC50 = 89.3 nM) and displayed significant amelioration on cognitive deficits in scopolamine-induced amnesia mice and efficient reduction against phosphorylation of tau protein on Ser-199 and Ser-396 sites in glyceraldehyde (GA)-stimulated differentiated SH-SY5Y cells. Furthermore, compound 27g exhibited eligible pharmacokinetic properties, good kinase selectivity, and moderate neuroprotection against GA-induced reduction in cell viability and neurite damage in SH-SY5Y-derived neurons. The multifunctional profiles of compound 27g suggest that it deserves further investigation as a promising lead for the prospective treatment of AD.

Design, Synthesis, and Molecular Docking of Some Novel Tacrine Based Cyclopentapyranopyridine- and Tetrahydropyranoquinoline-Kojic Acid Derivatives as Anti-Acetylcholinesterase Agents.

A novel series of tacrine based cyclopentapyranopyridine- and tetrahydropyranoquinoline-kojic acid derivatives were designed, synthesized, and evaluated as anti-cholinesterase agents. The chemical structures of all target compounds were characterized by 1 H-NMR, 13 C-NMR, and elemental analyses. The synthesized compounds mostly inhibited acetylcholinesterase enzyme (AChE) with IC50 values of 4.18-48.71 µM rather than butyrylcholinesterase enzyme (BChE) with IC50 values of >100 µM. Among them, cyclopentapyranopyridine-kojic acid derivatives showed slightly better AChE inhibitory activity compared to tetrahydropyranoquinoline-kojic acid. The compound 10-amino-2-(hydroxymethyl)-11-(4-isopropylphenyl)-7,8,9,11-tetrahydro-4H-cyclopenta[b]pyrano[2',3' : 5,6]pyrano[3,2-e]pyridin-4-one (6f) bearing 4-isopropylphenyl moiety and cyclopentane ring exhibited the highest anti-AChE activity with IC50 value of 4.18 µM. The kinetic study indicated that the compound 6f acts as a mixed inhibitor and the molecular docking studies also illustrated that the compound 6f binds to both the catalytic site (CS) and peripheral anionic site (PAS) of AChE. The compound 6f showed moderate neuroprotective properties against H2 O2 -induced cytotoxicity in PC12 cells. The theoretical ADME study also predicted good drug-likeness for the compound 6f. Based on these results, the compound 6f seems to be a very promising AChE inhibitor for the treatment of Alzheimer's disease.

Tacrine-Coumarin Derivatives as Topoisomerase Inhibitors with Antitumor Effects on A549 Human Lung Carcinoma Cancer Cell Lines.

A549 human lung carcinoma cell lines were treated with a series of new drugs with both tacrine and coumarin pharmacophores (derivatives 1a-2c) in order to test the compounds' ability to inhibit both cancer cell growth and topoisomerase I and II activity. The ability of human topoisomerase I (hTOPI) and II to relax supercoiled plasmid DNA in the presence of various concentrations of the tacrine-coumarin hybrid molecules was studied with agarose gel electrophoresis. The biological activities of the derivatives were studied using MTT assays, clonogenic assays, cell cycle analysis and quantification of cell number and viability. The content and localization of the derivatives in the cells were analysed using flow cytometry and confocal microscopy. All of the studied compounds were found to have inhibited topoisomerase I activity completely. The effect of the tacrine-coumarin hybrid compounds on cancer cells is likely to be dependent on the length of the chain between the tacrine and coumarin moieties (1c, 1d = tacrine-(CH2)8-9-coumarin). The most active of the tested compounds, derivatives 1c and 1d, both display longer chains.

Thieno[2,3-b]pyridine amines: Synthesis and evaluation of tacrine analogs against biological activities related to Alzheimer's disease.

In search of safer tacrine analogs, various thieno[2,3-b]pyridine amine derivatives were synthesized and evaluated for their inhibitory activity against cholinesterases (ChEs). Among the synthesized compounds, compounds 5e and 5d showed the highest activity towards acetylcholinesterase and butyrylcholinesterase, with IC50 values of 1.55 and 0.23 µM, respectively. The most active ChE inhibitors (5e and 5d) were also candidates for further complementary assays, such as kinetic and molecular docking studies as well as studies on inhibitory activity towards amyloid-beta (ßA) aggregation and ß-secretase 1, neuroprotectivity, and cytotoxicity against HepG2 cells. Our results indicated efficient anti-Alzheimer's activity of the synthesized compounds.

A Second Look at the Crystal Structures of Drosophila melanogaster Acetylcholinesterase in Complex with Tacrine Derivatives Provides Insights Concerning Catalytic Intermediates and the Design of Specific Insecticides.

Over recent decades, crystallographic software for data processing and structure refinement has improved dramatically, resulting in more accurate and detailed crystal structures. It is, therefore, sometimes valuable to have a second look at "old" diffraction data, especially when earlier interpretation of the electron density maps was rather difficult. Here, we present updated crystal structures of Drosophila melanogaster acetylcholinesterase (DmAChE) originally published in [Harel et al., Prot Sci (2000) 9:1063-1072], which reveal features previously unnoticed. Thus, previously unmodeled density in the native active site can be interpreted as stable acetylation of the catalytic serine. Similarly, a strong density in the DmAChE/ZA complex originally attributed to a sulfate ion is better interpreted as a small molecule that is covalently bound. This small molecule can be modeled as either a propionate or a glycinate. The complex is reminiscent of the carboxylate butyrylcholinesterase complexes observed in crystal structures of human butyrylcholinesterases from various sources, and demonstrates the remarkable ability of cholinesterases to stabilize covalent complexes with carboxylates. A very strong peak of density (10 σ) at covalent distance from the Cß of the catalytic serine is present in the DmAChE/ZAI complex. This can be undoubtedly attributed to an iodine atom, suggesting an unanticipated iodo/hydroxyl exchange between Ser238 and the inhibitor, possibly driven by the intense X-ray irradiation. Finally, the binding of tacrine-derived inhibitors, such as ZA (1DX4) or the iodinated analog, ZAI (1QON) results in the appearance of an open channel that connects the base of the active-site gorge to the solvent. This channel, which arises due to the absence of the conserved tyrosine present in vertebrate cholinesterases, could be exploited to design inhibitors specific to insect cholinesterases. The present study demonstrates that updated processing of older diffraction images, and the re-refinement of older diffraction data, can produce valuable information that could not be detected in the original analysis, and strongly supports the preservation of the diffraction images in public data banks.

A new fluorescent probe for sensing of biothiols and screening of acetylcholinesterase inhibitors.

A new N2O-type BODIPY probe (LF-Bop) has been proposed for the selective and sensitive detection of biologically relevant small molecular thiols. This detection is based on the Michael addition reaction between the thiol and nitrostyrene groups in the probe, which decreases the quenching effect from the nitro group, thus resulting in the recovery of the deep-red fluorescence from the BODIPY structure. The results show that LF-Bop is able to detect all tested free thiols through a fluorescence turn-on assay. The lowest limit of detection (LOD) for glutathione was found to be down to nanomolar levels (220 nM). Based on this probe, we have developed a new fluorescence assay for the screening of acetylcholinesterase inhibitors. In total, 11 natural and synthetic alkaloids have been evaluated. Both experimental measurements and theoretical molecular docking results reveal that both natural berberine and its synthetic derivative dihydroberberine are potential inhibitors of acetylcholinesterase.

Model Amphipathic Peptide Coupled with Tacrine to Improve Its Antiproliferative Activity.

Drug repurposing and drug combination are two strategies that have been widely used to overcome the traditional development of new anticancer drugs. Several FDA-approved drugs for other indications have been tested and have demonstrated beneficial anticancer effects. In this connection, our research group recently reported that Tacrine, used to treat Alzheimer's Disease, inhibits the growth of breast cancer MCF-7 cells both alone and in combination with a reference drug. In this view, we have now coupled Tacrine with the model amphipathic cell-penetrating peptide (CPP) MAP, to ascertain whether coupling of the CPP might enhance the drug's antiproliferative properties. To this end, we synthesized MAP through solid-phase peptide synthesis, coupled it with Tacrine, and made a comparative evaluation of the parent drug, peptide, and the conjugate regarding their permeability across the blood-brain barrier (BBB), ability to inhibit acetylcholinesterase (AChE) in vitro, and antiproliferative activity on cancer cells. Both MAP and its Tacrine conjugate were highly toxic to MCF-7 and SH-SY5Y cells. In turn, BBB-permeability studies were inconclusive, and conjugation to the CPP led to a considerable loss of Tacrine function as an AChE inhibitor. Nonetheless, this work reinforces the potential of repurposing Tacrine for cancer and enhances the antiproliferative activity of this drug through its conjugation to a CPP.

Synthesis and Cholinesterase Inhibitory Activity of N-Phosphorylated/ N-Tiophosphorylated Tacrine.

BACKGROUND: Alzheimer's disease (AD) is progressive and irreversible neurodegenerative disorder. Current pharmacotherapy is not able to stop progression of the disease and can only improve cognitive functions. Therefore, new drugs are being sought that will slow down the development of the disease. OBJECTIVE: Novel phosphorus and thiophosphorus tacrine derivatives 7-14 were designed, synthesized and their biological activity and molecular modeling was investigated as a new potential anti- Alzheimer's disease (AD) agents. METHODS: 9-Chlorotacrine was treated with propane-1,3-diamine in the presence of sodium iodide to yield N1-(1,2,3,4-tetrahydroacridin-9-yl)propane-1,3-diamine 6. Finally, it was treated with corresponding acid ester or thioester to give phosphorus or thiophosphorus tacrine derivative 7-14. All of the obtained final structures were characterized by 1H NMR, 13C NMR, 31P NMR and MS. RESULTS: The results of the docking studies showed that the newly designed phosphorus and thiophosphorus tacrine analogs, theoretically possess AChE and BChE-binding ability. Kinetic study showed that 8 and 12 in the series proved to be more potent electric eel AChE (eeAChE) and human (hAChE) inhibitors than tacrine, where 8 inhibited eeAChE three times more than the referenced drug. The highest BChE inhibition revealed 11 and 13. The most active compounds against eeAChE, hAChE and BChE showed mixed type of inhibition. CONCLUSION: All new synthesized compound exhibited lower toxicity against neuroblastoma.cell line (SH-SY5Y) in comparison with tacrine. Two analogues in the series, 7 and 9, demonstrated lack of cytotoxicity against hepatocellular cells (hepG2).

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

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 Aß 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 Aß1-42 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.

Tacrine-O-protected phenolics heterodimers as multitarget-directed ligands against Alzheimer's disease: Selective subnanomolar BuChE inhibitors.

Concerned by the devastating effects of Alzheimer's disease, and the lack of effective drugs, we have carried out the design of a series of tacrine-phenolic heterodimers in order to tackle the multifactorial nature of the disease. Hybridization of both pharmacophores involved the modification of the nature (imino, amino, ether) and the length of the tether, together with the type (hydroxy, methoxy, benzyloxy), number and position of the substituents on the aromatic residue. Title compounds were found to be strong and selective inhibitors of human BuChE (from low nanomolar to subnanomolar range), an enzyme that becomes crucial in the more advanced stages of the disease. The lead compound, bearing an ether-type tether, had an IC50 value of 0.52 nM against human BuChE, and a selectivity index of 323, with an 85-fold increase of activity compared to parent tacrine; key interactions were analysed using molecular modelling. Moreover, it also inhibited the self-aggregation of Aß42, lacking neurotoxicity up to 5 µM concentration, and showed neuroprotective activity in primary rat neurons in a serum and K+ deprivation model, widely employed for reproducing neuronal injury and senescence. Moreover, low hepatoxicity effects and complete stability under physiological conditions were found for that compound. So, overall, our lead compound can be considered as a promising multitarget-directed ligand against Alzheimer's disease, and a good candidate for developing new drugs.