Multifunctional tacrine–flavonoid hybrids with cholinergic, β-amyloid-reducing, and metal chelating properties for the treatment of Alzheimer's disease

Multifunctional iminochromene-2H-carboxamide derivatives containing different aminomethylene triazole with BACE1 inhibitory, neuroprotective and metal chelating properties targeting Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder known for the presence of amyloid beta plaques resulting from the sequential action of β-secretase and γ-secretase on amyloid precursor protein. We developed and synthesized, through click reactions, a new family of iminochromene carboxamides containing different aminomethylene triazole. The BACE1 inhibition, neuroprotective capacity and metal chelation of these derivatives make them ideal candidates against AD. Most of the synthesized compounds were shown to have potent BACE1 inhibitory activity in a FRET assay, with an IC₅₀ value of 2.2 μM for the most potent compound. Moreover, molecular modeling evaluation of these BACE1 inhibitors demonstrates the vital role of the amine and amide linkers through hydrogen bond interactions with key amino acids in the BACE1 active site. Our in vitro neuroprotective evaluations in PC12 neuronal cells of Aβ-induced neuroprotection demonstrated promising activity for most of the compounds as neuroprotective agents. Based on our findings, we propose that introduction of a phthalimide substitute on the triazole ring shown to be interesting multifunctional lead compound worthy of further study.

Discovery of novel isoflavone derivatives as AChE/BuChE dual-targeted inhibitors: synthesis, biological evaluation and molecular modelling

AChE and BuChE are druggable targets for the discovery of anti-Alzheimer’s disease drugs, while dual-inhibition of these two targets seems to be more effective. In this study, we synthesised a series of novel isoflavone derivatives based on our hit compound G from in silico high-throughput screening and then tested their activities by in vitro AChE and BuChE bioassays. Most of the isoflavone derivatives displayed moderate inhibition against both AChE and BuChE. Among them, compound 16 was identified as a potent AChE/BuChE dual-targeted inhibitor (IC₅₀: 4.60 μM for AChE; 5.92 μM for BuChE). Molecular modelling study indicated compound 16 may possess better pharmacokinetic properties, e.g. absorption, blood–brain barrier penetration and CYP2D6 binding. Taken together, our study has identified compound 16 as an excellent lead compound for the treatment of Alzheimer’s disease.

Design, synthesis, biological evaluation, and molecular docking of novel flavones as H3 R inhibitors

A series of novel flavone derivatives were designed, synthesized, and evaluated for their H₃ R inhibitory activity. The results showed that four compounds exhibited significant anti-H₃ R activity. Molecular docking experiments indicated that a salt bridge, hydrogen-bonding, and hydrophobic interactions all contributed to interactions between inhibitors and H₃ R.

Recent advances in acetylcholinesterase Inhibitors and Reactivators: an update on the patent literature (2012-2015)

INTRODUCTION

Acetylcholinesterase (AChE) is the major enzyme that hydrolyzes acetylcholine, a key neurotransmitter for synaptic transmission, into acetic acid and choline. Mild inhibition of AChE has been shown to have therapeutic relevance in Alzheimer's disease (AD), myasthenia gravis, and glaucoma among others. In contrast, strong inhibition of AChE can lead to cholinergic poisoning. To combat this, AChE reactivators have to be developed to remove the offending AChE inhibitor, restoring acetylcholine levels to normal. Areas covered: This article covers recent advances in the development of acetylcholinesterase modulators, including both inhibitors of acetylcholinesterase for the efforts in development of new chemical entities for treatment of AD, as well as re-activators for resurrection of organophosphate bound acetylcholinesterase. Expert opinion: Over the past three years, research efforts have continued to identify novel small molecules as AChE inhibitors for both CNS and peripheral diseases. The more recent patent activity has focused on three AChE ligand design areas: derivatives of known AChE ligands, natural product based scaffolds and multifunctional ligands, all of which have produced some unique chemical matter with AChE inhibition activities in the mid picomolar to low micromolar ranges. New AChE inhibitors with polypharmacology or dual inhibitory activity have also emerged as highlighted by new AChE inhibitors with dual activity at L-type calcium channels, GSK-3, BACE1 and H3, although most only show low micromolar activity, thus further research is warranted. New small molecule reactivators of organophosphate-inhibited AChE have also been disclosed, which focused on the design of neutral ligands with improved pharmaceutical properties and blood-brain barrier (BBB) penetration. Gratifyingly, some research in this area is moving away from the traditional quaternary pyridinium oximes AChE reactivators, while still employing the necessary reactivation group (oximes). However, selectivity over inhibition of native AChE enzyme, effectiveness of reactivation, broad-spectrum reactivation against multiple organophosphates and reactivation of aged-enzyme continue to be hurdles for this area of research.

Combinatorial Synthesis of Structurally Diverse Triazole-Bridged Flavonoid Dimers and Trimers

Flavonoids are a large family of compounds associated with a broad range of biologically useful properties. In recent years, synthetic compounds that contain two flavonoid units linked together have attracted attention in drug discovery and development projects. Numerous flavonoid dimer systems, incorporating a range of monomers attached via different linkers, have been reported to exhibit interesting bioactivities. From a medicinal chemistry perspective, the 1,2,3-triazole ring system has been identified as a particularly attractive linker moiety in dimeric derivatives (owing to several favourable attributes including proven biological relevance and metabolic stability) and triazole-bridged flavonoid dimers possessing anticancer and antimalarial activities have recently been reported. However, there are relatively few examples of libraries of triazole-bridged flavonoid dimers and the diversity of flavonoid subunits present within these is typically limited. Thus, this compound type arguably remains underexplored within drug discovery. Herein, we report a modular strategy for the synthesis of novel and biologically interesting triazole-bridged flavonoid heterodimers and also very rare heterotrimers from readily available starting materials. Application of this strategy has enabled step-efficient and systematic access to a library of structurally diverse compounds of this sort, with a variety of monomer units belonging to six different structural subclasses of flavonoid successfully incorporated.

Rational modification of donepezil as multifunctional acetylcholinesterase inhibitors for the treatment of Alzheimer's disease

A series of novel donepezil derivatives was designed, synthesized and evaluated as multifunctional acetylcholinesterase (AChE) inhibitors for the treatment of Alzheimer's disease (AD). The screening results indicated that most of the compounds exhibited potent inhibition of AChE with IC50 values in the nanomolar range. Moreover, these derivatives displayed good antioxidant, Aβ interaction, blood-brain barrier penetration (PAMPA-BBB+) and ADMET properties (in silico). Among them, 5c demonstrated excellent AChE inhibition (IC50: 85 nM for eeAChE, 73 nM for hAChE), metal chelation, and inhibitory effects on self-induced, hAChE-induced and Cu(2+)-induced Aβ1-42 aggregation (18.5%, 72.4% and 46.3%, at 20 μM). Kinetic analysis and molecular modeling studies suggested that 5c could bind simultaneously to the catalytic active site (CAS) and peripheral anionic site (PAS) of AChE. More importantly, 5c exhibited significant neuroprotective potency against Aβ1-42-induced PC12 cell injury. Furthermore, the step-through passive avoidance test showed 5c significantly reversed scopolamine-induced memory deficit and no hepatotoxicity in mice. These results indicated that 5c might be a promising drug candidate for AD therapy.

Synthesis and evaluation of multi-target-directed ligands for the treatment of Alzheimer's disease based on the fusion of donepezil and melatonin

A novel series of compounds obtained by fusing the acetylcholinesterase (AChE) inhibitor donepezil and the antioxidant melatonin were designed as multi-target-directed ligands for the treatment of Alzheimer's disease (AD). In vitro assay indicated that most of the target compounds exhibited a significant ability to inhibit acetylcholinesterase (eeAChE and hAChE), butyrylcholinesterase (eqBuChE and hBuChE), and β-amyloid (Aβ) aggregation, and to act as potential antioxidants and biometal chelators. Especially, 4u displayed a good inhibition of AChE (IC50 value of 193nM for eeAChE and 273nM for hAChE), strong inhibition of BuChE (IC50 value of 73nM for eqBuChE and 56nM for hBuChE), moderate inhibition of Aβ aggregation (56.3% at 20μM) and good antioxidant activity (3.28trolox equivalent by ORAC assay). Molecular modeling studies in combination with kinetic analysis revealed that 4u was a mixed-type inhibitor, binding simultaneously to catalytic anionic site (CAS) and the peripheral anionic site (PAS) of AChE. In addition, 4u could chelate metal ions, reduce PC12 cells death induced by oxidative stress and penetrate the blood-brain barrier (BBB). Taken together, these results strongly indicated the hybridization approach is an efficient strategy to identify novel scaffolds with desired bioactivities, and further optimization of 4u may be helpful to develop more potent lead compound for AD treatment.

DADS Analogues Ameliorated the Cognitive Impairments of Alzheimer-Like Rat Model Induced by Scopolamine

The development of agents that affect two or more relevant targets has drawn considerable attention in treatment of AD. Diallyl disulfide (DADS), an active principle of garlic, has been reported to prevent APP processing by amyloidogenic pathway. Recently, we have reported a new series of DADS derivatives and our findings revealed that compound 7k and 7l could provide good templates for developing new multifunctional agents for AD treatment. Thus, the present study was constructed to investigate the neuroprotective effect of DADS analogues (7k and 7l) against Aβ-induced neurotoxicity in SH-SY5Y human neuroblastoma cells and in ameliorating the cognition deficit induced by scopolamine in rat model. The results indicated that compound 7k and 7l significantly inhibited Aβ1-42-induced neuronal cell death by inhibiting ROS generation. Moreover, they prevented apoptosis, in response to ROS, by restoring normal Bax/Bcl-2 ratio. Furthermore, it was observed that scopolamine-induced memory impairment was coupled by alterations in neurotransmitters, acetylcholinesterase activity and oxidative stress markers. Histological analysis revealed severe damaging effects of scopolamine on the structure of cerebral cortex and hippocampus. Administration of compounds 7k and 7l at 5 mg/kg significantly reversed scopolamine-induced behavioural, biochemical, neurochemical and histological changes in a manner comparable to standard donepezil. Together the present findings and previous studies indicate that compounds 7k and 7l have neuroprotective and cognition-enhancing effects, which makes them a promising multi-target candidate for addressing the complex nature of AD.

Combined 3D-QSAR, molecular docking, and molecular dynamics study of tacrine derivatives as potential acetylcholinesterase (AChE) inhibitors of Alzheimer's disease

Acetylcholinesterase (AChE) is one of the key targets of drugs for treating Alzheimer's disease (AD). Tacrine is an approved drug with AChE-inhibitory activity. In this paper, 3D-QSAR, molecular docking, and molecular dynamics were carried out in order to study 60 tacrine derivatives and their AChE-inhibitory activities. 3D-QSAR modeling resulted in an optimal CoMFA model with q(2) = 0.552 and r(2) = 0.983 and an optimal CoMSIA model with q(2) = 0.581 and r(2) = 0.989. These QSAR models also showed that the steric and H-bond fields of these compounds are important influences on their activities. The interactions between these inhibitors and AChE were further explored through molecular docking and molecular dynamics simulation. A few key residues (Tyr70, Trp84, Tyr121, Trp279, and Phe330) at the binding site of AChE were identified. The results of this study improve our understanding of the mechanisms of AChE inhibitors and afford valuable information that should aid the design of novel potential AChE inhibitors. Graphical Abstract Superposition of backbone atoms of the lowest-energy structure obtained from MD simulation (magenta) onto those of the structure of the initial molecular docking model (green).

Design, synthesis and evaluation of novel 5,6,7-trimethoxyflavone-6-chlorotacrine hybrids as potential multifunctional agents for the treatment of Alzheimer's disease

A series of 5,6,7-trimethoxyflavone-6-chlorotacrine hybrids were designed, synthesized and evaluated as multifunctional agents for the treatment of Alzheimer's disease (AD). The results showed that the target compounds exhibited good acetylcholinesterase (AChE) inhibitory potencies, high selectivity toward AChE over butyrylcholinesterase (BuChE), potential antioxidant activities and significant inhibitory potencies of self-induced beta-amyloid peptide (Aβ) aggregation. In particular, compound 14c had the strongest AChE inhibitory activity with IC50 value of 12.8 nM, potent inhibition of self-induced Aβ1-42 aggregation with inhibition ratio of 33.8% at 25 μM. Moreover, compound 14c acted as an antioxidant, as well as a neuroprotectant. Furthermore, 14c could cross the blood-brain barrier (BBB) in vitro. The results showed that compound 14c might be a potential multifunctional candidate for the treatment of AD.

Isoindoline-1,3-dione derivatives targeting cholinesterases: design, synthesis and biological evaluation of potential anti-Alzheimer's agents

Alzheimer's disease is a fatal neurodegenerative disorder with a complex etiology. Because the available therapy brings limited benefits, the effective treatment for Alzheimer's disease remains the unmet challenge. Our aim was to develop a new series of donepezil-based compounds endowed with inhibitory properties against cholinesterases and β-amyloid aggregation. We designed the target compounds as dual binding site acetylcholinesterase inhibitors with N-benzylamine moiety interacting with the catalytic site of the enzyme and an isoindoline-1,3-dione fragment interacting with the peripheral anionic site of the enzyme. The results of pharmacological evaluation lead us to identify a compound 3b as the most potent and selective human acetylcholinesterase inhibitor (hAChE IC50=0.361μM). Kinetic studies revealed that 3b inhibited acetylcholinesterase in non-competitive mode. The result of the parallel artificial membrane permeability assay for the blood-brain barrier indicated that the compound 3b would be able to cross the blood-brain barrier and reach its biological targets in the central nervous system. The selected compound 3b represents a potential lead structure for further development of anti-Alzheimer's agents.

Development of multifunctional, heterodimeric isoindoline-1,3-dione derivatives as cholinesterase and β-amyloid aggregation inhibitors with neuroprotective properties

The presented study describes the synthesis, pharmacological evaluation (AChE and BuChE inhibition, beta amyloid anti-aggregation effect and neuroprotective effect), molecular modeling and crystallographic studies of a novel series of isoindoline-1,3-dione derivatives. The target compounds were designed as dual binding site acetylcholinesterase inhibitors with an arylalkylamine moiety binding at the catalytic site of the enzyme and connected via an alkyl chain to a heterocyclic fragment, capable of binding at the peripheral anionic site of AChE. Among these molecules, compound 15b was found to be the most potent and selective AChE inhibitor (IC50EeAChE = 0.034 μM). Moreover, compound 13b in addition to AChE inhibition (IC50 EeAChE = 0.219 μM) possesses additional properties, such as the ability to inhibit Aβ aggregation (65.96% at 10 μM) and a neuroprotective effect against Aβ toxicity at 1 and 3 μM. Compound 13b emerges as a promising multi-target ligand for the further development of the therapy for age-related neurodegenerative disorders.

Recent development of multifunctional agents as potential drug candidates for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a complex and progressive neurodegenerative disorder. The available therapy is limited to the symptomatic treatment and its efficacy remains unsatisfactory. In view of the prevalence and expected increase in the incidence of AD, the development of an effective therapy is crucial for public health. Due to the multifactorial aetiology of this disease, the multi-target-directed ligand (MTDL) approach is a promising method in search for new drugs for AD. This review updates information on the development of multifunctional potential anti-AD agents published within the last three years. The majority of the recently reported structures are acetylcholinesterase inhibitors, often endowed with some additional properties. These properties enrich the pharmacological profile of the compounds giving hope for not only symptomatic but also causal treatment of the disease. Among these advantageous properties, the most often reported are an amyloid-β antiaggregation activity, inhibition of β-secretase and monoamine oxidase, an antioxidant and metal chelating activity, NOreleasing ability and interaction with cannabinoid, NMDA or histamine H3 receptors. The majority of novel molecules possess heterodimeric structures, able to interact with multiple targets by combining different pharmacophores, original or derived from natural products or existing therapeutics (tacrine, donepezil, galantamine, memantine). Among the described compounds, several seem to be promising drug candidates, while others may serve as a valuable inspiration in the search for new effective therapies for AD.

Hybrid curcumin compounds: a new strategy for cancer treatment

Cancer is a multifactorial disease that requires treatments able to target multiple intracellular components and signaling pathways. The natural compound, curcumin, was already described as a promising anticancer agent due to its multipotent properties and huge amount of molecular targets in vitro. Its translation to the clinic is, however, limited by its reduced solubility and bioavailability in patients. In order to overcome these pharmacokinetic deficits of curcumin, several strategies, such as the design of synthetic analogs, the combination with specific adjuvants or nano-formulations, have been developed. By taking into account the risk-benefit profile of drug combinations, as well as the knowledge about curcumin's structure-activity relationship, a new concept for the combination of curcumin with scaffolds from different natural products or components has emerged. The concept of a hybrid curcumin molecule is based on the incorporation or combination of curcumin with specific antibodies, adjuvants or other natural products already used or not in conventional chemotherapy, in one single molecule. The high diversity of such conjugations enhances the selectivity and inherent biological activities and properties, as well as the efficacy of the parental compound, with particular emphasis on improving the efficacy of curcumin for future clinical treatments.

Synthesis, leishmanicidal and cytotoxic activity of triclosan-chalcone, triclosan-chromone and triclosan-coumarin hybrids

Twelve hybrids derived from triclosan were obtained via Williamson etherification of O-triclosan alkyl bromide plus chalcone and O-coumarin or O-chromone alkyl bromide plus triclosan, respectively. Structures of the products were elucidated by spectroscopic analysis. The synthesized compounds were evaluated for antileishmanial activity against L. (V) panamensis amastigotes. Cytotoxic activity was also evaluated against mammalian U-937 cells. Compounds 7-9 and 17, were active against Leishmania parasites (EC50=9.4; 10.2; 13.5 and 27.5 µg/mL, respectively) and showed no toxicity toward mammalian cells (>200 µg/mL). They are potential candidates for antileishmanial drug development. Compounds 25-27, were active and cytotoxic. Further studies using other cell types are needed in order to discriminate whether the toxicity shown by these compounds is against tumor or non-tumor cells. The results indicate that compounds containing small alkyl chains show better selectivity indices. Moreover, Michael acceptor moieties may modify both the leishmanicidal activity and cytotoxicity. Further studies are required to evaluate if the in vitro activity against Leishmania panamensis demonstrated here is also observed in vivo.