Targeting Alzheimer’s disease: Novel indanone hybrids bearing a pharmacophoric fragment of AP2238

Synthesis and biological evaluation of a new series of ebselen derivatives as glutathione peroxidase (GPx) mimics and cholinesterase inhibitors against Alzheimer's disease

A series of ebselen derivatives were designed, synthesised and evaluated as inhibitors of cholinesterases (ChEs) and glutathione peroxidase (GPx) mimics. Most of the compounds were found to be potent against AChEs and BuChE, compounds 5e and 5i, proved to be the most potent against AChE with IC₅₀ values of 0.76 and 0.46 μM, respectively. Among these hybrids, most of the compounds were found to be good GPx mimics compare with ebselen. The selected compounds 5e and 5i were also used to determine the catalytic parameters and in vitro hydrogen peroxide scavenging activity. The results indicate that compounds 5e and 5i may be excellent multifunctional agents for the treatment of AD.

Structural analysis of 2-arylidene-1-indanone derivatives by electrospray ionization tandem mass spectrometry

RATIONALE

2-arylidene-4-methoxy (or hydroxy)-7-methyl-1-indanone derivatives inspired from donepezil, the current drug used for the treatment of Alzheimer's disease as inhibitor of acetylcholinesterase (AChE), were studied for the first time by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). Structurally, these arylidene-indanone compounds are considered as cyclic analogues of chalcones.

METHODS

ESI-MS and tandem mass spectra were acquired using a Q-TOF 2 instrument. Fragmentation patterns were analyzed by CID-MS(2-3) spectra acquired in a Q-TOF and in LXQ linear ion trap mass spectrometers using standard isolation and excitation procedures.

RESULTS

All the 2-arylidene indanones have shown a common fragmentation pathway leading to a (2(1), 1')A(+) product ion at m/z 187 and the retro-aldol product ion [(2, 2(1))B(+)] that allow to establish the substitution in the B ring. The effect of electron-donating and -withdrawing substituents on these fragmentation pathways was noticed. The presence of the OCH3, OH, NO2 and Br substituents gave typical fragmentation processes that allowed their unequivocal fingerprinting. The combined loss of the ortho substituent in the B-ring plus hydrogen (H, OCH3, Br and F) is proposed to form a stable cyclic ring product.

CONCLUSIONS

Arylidene indanones with different substituents on the B ring are associated with a specific fragmentation pattern. In addition, differentiation between isomers with substituents in B ring at ortho and para positions were achieved using ESI-MS/MS. These fragmentation pathways can be used to further identify and determine the fate of these molecules in all stages of drug discovery.

Synthesis of bistetrahydroquinolines as potential anticholinesterasic agents by double Diels-Alder reactions

The tetrahydroquinoline ring system is a unit found in many biologically active natural products and pharmacologically relevant therapeutic agents. A new series of bistetrahydroquinolines (bis-THQs) was synthesized using imino Diels-Alder reactions between dialdehydes, anilines and N-vinyl-2-pyrrolidone (NVP). The notable features of this procedure are mild reaction conditions, greater selectivity and good yields of products. In addition, the inhibitory activity against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) of some selected derivatives is reported. The feasible binding modes of these active compounds, within AChE and BuChE binding sites, were predicted by molecular docking experiments and their binding affinity was estimated by means of free energy calculations through the MM-GBSA approximation.

Synthesis, pharmacological assessment, and molecular modeling of 6-chloro-pyridonepezils: new dual AChE inhibitors as potential drugs for the treatment of Alzheimer's disease

6-Chloro-pyridonepezils are chloropyridine-donepezil hybrids designed by combining the N-benzylpiperidine moiety present in donepezil with the 2-chloropyridine-3,5-dicarbonitrile heterocyclic ring system, both connected by an appropriate polymethylene linker. 6-Chloro-pyridonepezils1-8 were prepared by reaction of 2,6-dichloro-4-phenylpyridine-3,5-dicarbonitrile (13) [or 2,6-dichloropyridine-3,5-dicarbonitrile (14)] with suitable 2-(1-benzylpiperidin-4-yl)alkylamines (9-12). The biological evaluation showed that these new compounds are cholinesterase inhibitors, in the submicromolar range, one of them (6) being a potent hBuChE inhibitor (IC50 = 0.47 ± 0.08 μM). 6-Chloro-pyridonepezils4, 7 and 8 are potent hAChE inhibitors showing IC50 in the 0.013-0.054 μM range. Particularly, 6-chloro-pyridonepezil8 is 625-fold more selective for hAChE than for hBuChE and compared to donepezil is equipotent for the inhibition of hAChE. Molecular modeling investigation on 6-chloro-pyridonepezils4, 6-8 supports its dual AChE inhibitory profile, by binding simultaneously at the catalytic active and at peripheral anionic sites of the enzyme. The in vitro Blood Brain Barrier (BBB) and theoretical ADME analysis of 6-chloro-pyridonepezils1-8 have been carried out. Overall, compound 8, is a permeable potent and selective dual AChEI that can be considered as a good candidate with potential impact for further pharmacological development in Alzheimer's therapy.

Biological activity of sym-triazines with acetylcholine-like substitutions as multitarget modulators of Alzheimer's disease

The bioactivities of two novel compounds (TAE-1 and TAE-2) that contain a sym-triazine scaffold with acetylcholine-like substitutions are examined as promising candidate agents against Alzheimer's disease. Inhibition of amyloid-β fibril formation in the presence of Aβ1-42, evaluated by Thioflavin T fluorescence, demonstrated comparable or improved activity to a previously reported pentapeptide-based fibrillogenesis inhibitor, iAβ5p. Destabilization of Aβ1-42 assemblies by TAE-1 and TAE-2 was confirmed by scanning electron microscopy imaging. sym-Triazine inhibition of acetylcholinesterase (AChE) activity was observed in cytosol extracted from differentiated human SH-SY5Y neuronal cells and also using human erythrocyte AChE. The sym-triazine derivatives were well tolerated by these cells and promoted beneficial effects on human neurons, upregulating expression of synaptophysin, a synaptic marker protein, and MAP2, a neuronal differentiation marker.

Pyridonepezils, new dual AChE inhibitors as potential drugs for the treatment of Alzheimer's disease: synthesis, biological assessment, and molecular modeling

The synthesis, biological assessment and molecular modeling of new pyridonepezils1-8, able to inhibit human acetylcholinesterase (hAChE) and human butyrylcholinesterase (hBuChE), are described. The new compounds have been designed as hybrids resulting from a conjunctive approach that combines the N-benzylpiperidine moiety, present in donepezil, and the 2-amino-6-chloropyridine heterocyclic ring system, connected by an appropriate polymethylene linker. Compounds 1-8 were prepared by reaction of 2-amino-6-chloro-4-phenylpyridine-3,5-dicarbonitrile (13) [or 2-amino-6-chloropyridine-3,5-dicarbonitrile (14)] with 2-(1-benzylpiperidin-4-yl)alkylamines (9-12). The biological evaluation of molecules 1-8 showed that compounds 1-6 are potent AChE inhibitors, in the submicromolar, while compounds 7 and 8 are on the nanomolar range, the most potent, 2-amino-6-((3-(1-benzylpiperidin-4-yl)propyl)amino)pyridine-3,5-dicarbonitrile (7), showing a IC(50) (hAChE) = 9.4 ± 0.4 nM. Inhibitors 2-8 are permeable as determined in the PAMPA assay. Compared to donepezil, compound 7 is in the same range of inhibitory activity for hAChE, and 703-fold more selective for hAChE than for hBuChE. Molecular modeling investigation on pyridonepezil7 supports its dual AChE inhibitory profile, binding simultaneously at the catalytic active and at peripheral anionic sites of the enzyme. The theoretical ADME analysis of pyridonepezils1-8 has been carried out. Overall, compound 7, a potent and selective dual AChEI, can be considered as a candidate with potential impact for further pharmacological development in Alzheimer's therapy.

Application of conformational clustering in protein-ligand docking

Protein-Ligand docking is a powerful technique routinely employed in structure-based drug design. Despite many reported success stories, docking is not always able to provide an accurate and easily interpretable prediction of the structure of the bound complex formed by a small organic molecule and a pharmacologically relevant target. Cluster analysis can represent a versatile and readily available postprocessing tool to be employed in combination with protein-ligand docking to simplify the evaluation of the results and help to overcome present limitations of docking protocols.

New acetylcholinesterase inhibitors for Alzheimer's disease

Acetylcholinesterase (AChE) remains a highly viable target for the symptomatic improvement in Alzheimer's disease (AD) because cholinergic deficit is a consistent and early finding in AD. The treatment approach of inhibiting peripheral AchE for myasthenia gravis had effectively proven that AchE inhibition was a reachable therapeutic target. Subsequently tacrine, donepezil, rivastigmine, and galantamine were developed and approved for the symptomatic treatment of AD. Since then, multiple cholinesterase inhibitors (ChEI) continue to be developed. These include newer ChEIs, naturally derived ChEIs, hybrids, and synthetic analogues. In this paper, we summarize the different types of ChEIs in development and their respective mechanisms of actions. This pharmacological approach continues to be active with many promising compounds.

Cognitive Enhancers in Moderate to Severe Alzheimer's Disease

The treatment of moderate to severe Alzheimer's disease is reviewed with regard to mechanisms of action, pharmacokinetics, metabolism, safety/tolerability, and efficacy in reducing cognitive, behavioral/psychiatric, functional and global symptoms. The cholinesterase inhibitors donepezil, rivastigmine and galantamine and the N-methyl-d-aspartate receptor channel blocker memantine are moderately beneficial. Small improvements over a few months are followed by slowed mental decline. Concerning cognitive, functional and global functions, these drugs are similarly effective. Cholinesterase inhibitors also reduce apathy, memantine counteracts agitation and aggression. Serious adverse effects are rare with all four drugs. Cholinesterase inhibitors bear a risk for patients with cardiac diseases. Adverse emetic events are typical for oral formulations of these drugs, but less for rivastigmine transdermal patches. Other routes of administration and use of a galantamine prodrug are currently investigated. The superiority of combination therapies over monotherapies requires further support. Promising investigational drugs include the copper/zinc ionophore PBT2 and multifunctional hybrid molecules.

Alzheimer's disease and age-related memory decline (preclinical)

An unfortunate result of the rapid rise in geriatric populations worldwide is the increasing prevalence of age-related cognitive disorders such as Alzheimer's disease (AD). AD is a devastating neurodegenerative illness that is characterized by a profound impairment of cognitive function, marked physical disability, and an enormous economic burden on the afflicted individual, caregivers, and society in general. The rise in elderly populations is also resulting in an increase in individuals with related (potentially treatable) conditions such as "Mild Cognitive Impairment" (MCI) which is characterized by a less severe (but abnormal) level of cognitive impairment and a high-risk for developing dementia. Even in the absence of a diagnosable disorder of cognition (e.g., AD and MCI), the perception of increased forgetfulness and declining mental function is a clear source of apprehension in the elderly. This is a valid concern given that even a modest impairment of cognitive function is likely to be associated with significant disability in a rapidly evolving, technology-based society. Unfortunately, the currently available therapies designed to improve cognition (i.e., for AD and other forms of dementia) are limited by modest efficacy and adverse side effects, and their effects on cognitive function are not sustained over time. Accordingly, it is incumbent on the scientific community to develop safer and more effective therapies that improve and/or sustain cognitive function in the elderly allowing them to remain mentally active and productive for as long as possible. As diagnostic criteria for memory disorders evolve, the demand for pro-cognitive therapeutic agents is likely to surpass AD and dementia to include MCI and potentially even less severe forms of memory decline. The purpose of this review is to provide an overview of the contemporary therapeutic targets and preclinical pharmacologic approaches (with representative drug examples) designed to enhance memory function.