Neuroprotective and Antioxidant Properties of CholesteroNitrone ChN2 and QuinolylNitrone QN23 in an Experimental Model of Cerebral Ischemia: Involvement of Necrotic and Apoptotic Cell Death

Ischemic stroke is the leading cause of disability and the second leading cause of death worldwide. However, current therapeutic strategies are scarce and of limited efficacy. The abundance of information available on the molecular pathophysiology of ischemic stroke has sparked considerable interest in developing new neuroprotective agents that can target different events of the ischemic cascade and may be used in combination with existing treatments. In this regard, nitrones represent a very promising alternative due to their renowned antioxidant and anti-inflammatory effects. In this study, we aimed to further investigate the neuroprotective effects of two nitrones, cholesteronitrone 2 (ChN2) and quinolylnitrone 23 (QN23), which have previously shown great potential for the treatment of stroke. Using an experimental in vitro model of cerebral ischemia, we compared their anti-necrotic, anti-apoptotic, and antioxidant properties with those of three reference compounds. Both ChN2 and QN23 demonstrated significant neuroprotective effects (EC₅₀ = 0.66 ± 0.23 μM and EC₅₀ = 2.13 ± 0.47 μM, respectively) comparable to those of homo-bis-nitrone 6 (HBN6) and N-acetylcysteine (NAC) and superior to those of α-phenyl-N-tert-butylnitrone (PBN). While primarily derived from the nitrones' anti-necrotic capacities, their anti-apoptotic effects at high concentrations and antioxidant powers-especially in the case of QN23-also contribute to their neuroprotective effects.

The Chemotype of Chromanones as a Privileged Scaffold for Multineurotarget Anti-Alzheimer Agents

The multifactorial nature of Alzheimer's disease necessitates the development of agents able to interfere with different relevant targets. A series of 22 tailored chromanones was conceptualized, synthesized, and subjected to biological evaluation. We identified one representative bearing a linker-connected azepane moiety (compound 19) with balanced pharmacological properties. Compound 19 exhibited inhibitory activities against human acetyl-, butyrylcholinesterase and monoamine oxidase-B, as well as high affinity to both the σ1 and σ2 receptors. Our study provides a framework for the development of further chromanone-based multineurotarget agents.

Postischemic Neuroprotection of Aminoethoxydiphenyl Borate Associates Shortening of Peri-Infarct Depolarizations

Brain stroke is a highly prevalent pathology and a main cause of disability among older adults. If not promptly treated with recanalization therapies, primary and secondary mechanisms of injury contribute to an increase in the lesion, enhancing neurological deficits. Targeting excitotoxicity and oxidative stress are very promising approaches, but only a few compounds have reached the clinic with relatively good positive outcomes. The exploration of novel targets might overcome the lack of clinical translation of previous efficient preclinical neuroprotective treatments. In this study, we examined the neuroprotective properties of 2-aminoethoxydiphenyl borate (2-APB), a molecule that interferes with intracellular calcium dynamics by the antagonization of several channels and receptors. In a permanent model of cerebral ischemia, we showed that 2-APB reduces the extent of the damage and preserves the functionality of the cortical territory, as evaluated by somatosensory evoked potentials (SSEPs). While in this permanent ischemia model, the neuroprotective effect exerted by the antioxidant scavenger cholesteronitrone F2 was associated with a reduction in reactive oxygen species (ROS) and better neuronal survival in the penumbra, 2-APB did not modify the inflammatory response or decrease the content of ROS and was mostly associated with a shortening of peri-infarct depolarizations, which translated into better cerebral blood perfusion in the penumbra. Our study highlights the potential of 2-APB to target spreading depolarization events and their associated inverse hemodynamic changes, which mainly contribute to extension of the area of lesion in cerebrovascular pathologies.

Privileged Quinolylnitrones for the Combined Therapy of Ischemic Stroke and Alzheimer's Disease

Cerebrovascular diseases such as ischemic stroke are known to exacerbate dementia caused by neurodegenerative pathologies such as Alzheimer’s disease (AD). Besides, the increasing number of patients surviving stroke makes it necessary to treat the co-occurrence of these two diseases with a single and combined therapy. For the development of new dual therapeutic agents, eight hybrid quinolylnitrones have been designed and synthesized by the juxtaposition of selected pharmacophores from our most advanced lead-compounds for ischemic stroke and AD treatment. Biological analyses looking for efficient neuroprotective effects in suitable phenotypic assays led us to identify MC903 as a new small quinolylnitrone for the potential dual therapy of stroke and AD, showing strong neuroprotection on (i) primary cortical neurons under oxygen–glucose deprivation/normoglycemic reoxygenation as an experimental ischemia model; (ii), neuronal line cells treated with rotenone/oligomycin A, okadaic acid or β-amyloid peptide Aβ_25–35, modeling toxic insults found among the effects of AD.

In Vitro and In Silico ADME-Tox Profiling and Safety Significance of Multifunctional Monoamine Oxidase Inhibitors Targeting Neurodegenerative Diseases

Herein we report in vitro metabolic stability in human liver microsomes (HLMs), interactions with cytochrome P450 isoenzymes (CYP3A4, CYP2D6, and CYP2C9), and cytotoxicity analyses on HEK-293, HepG2, Huh7, and WTIIB cell lines of our most recent multitarget directed ligands PF9601N, ASS234, and contilisant. Based on these results, we conclude that (1) PF9601N and contilisant are metabolically stable in the HLM assay, in contrast to the very unstable ASS234; (2) CYP3A4 activity was decreased by PF9601N at all the tested concentrations and by ASS234 and contilisant only at the highest concentration; CYP2D6 activity was reduced by ASS234 at 1, 10, and 25 μM and by PF9601N at 10 and 25 μM, whereas contilisant increased its activity at the same concentrations; CYP2C9 was inhibited by the three compounds; (3) contilisant did not affect cell viability in the widest range of concentrations: up to 10 μM on HEK-293 cells, up to 30 μM on Huh7 cells, up to 50 μM on HepG2 cells, and up to 30 or 100 μM on WTIIB cells. Based on these results, we selected contilisant as a metabolically stable and nontoxic lead compound for further studies in Alzheimer’s disease therapy.

Chromenones as Multineurotargeting Inhibitors of Human Enzymes

The complex nature of multifactorial diseases, such as Morbus Alzheimer, has produced a strong need to design multitarget-directed ligands to address the involved complementary pathways. We performed a purposive structural modification of a tetratarget small-molecule, that is contilisant, and generated a combinatorial library of 28 substituted chromen-4-ones. The compounds comprise a basic moiety which is linker-connected to the 6-position of the heterocyclic chromenone core. The syntheses were accomplished by Mitsunobu- or Williamson-type ether formations. The resulting library members were evaluated at a panel of seven human enzymes, all of which being involved in the pathophysiology of neurodegeneration. A concomitant inhibition of human acetylcholinesterase and human monoamine oxidase B, with IC₅₀ values of 5.58 and 7.20 μM, respectively, was achieved with the dual-target 6-(4-(piperidin-1-yl)butoxy)-4H-chromen-4-one (7).

Novel Quinolylnitrones Combining Neuroprotective and Antioxidant Properties

We describe here the preparation, neuroprotective analysis, and antioxidant capacity of 11 novel quinolylnitrones (QN). The neuroprotective analysis of QN1-11 in an oxygen-glucose deprivation model, in primary neuronal cultures, has been determined, allowing us to identify QN6 as a very potent neuroprotective agent, showing significant high value at 0.5 and 10 μM (86.2%), a result in good agreement with the observed strong hydroxyl radical scavenger of QN6.

New Quinolylnitrones for Stroke Therapy: Antioxidant and Neuroprotective ( Z)- N- tert-Butyl-1-(2-chloro-6-methoxyquinolin-3-yl)methanimine Oxide as a New Lead-Compound for Ischemic Stroke Treatment

We describe herein the synthesis and neuroprotective capacity of an array of 31 compounds comprising quinolyloximes, quinolylhydrazones, quinolylimines, QNs, and related heterocyclic azolylnitrones. Neuronal cultures subjected to oxygen-glucose deprivation (OGD), as experimental model for ischemic conditions, were treated with our molecules at the onset of recovery period after OGD and showed that most of these QNs, but not the azo molecules, improved neuronal viability 24 h after recovery. Especially, QN ( Z)- N-tert-butyl-1-(2-chloro-6-methoxyquinolin-3-yl)methanimine oxide (23) was shown as a very potent neuroprotective agent. Antioxidant analysis based on the ability of QN 23 to trap different types of toxic radical oxygenated species supported and confirmed its strong neuroprotective capacity. Finally, QN 23 showed also neuroprotection induction in two in vivo models of cerebral ischemia, decreasing neuronal death and reducing infarct size, allowing us to conclude that QN 23 can be considered as new lead-compound for ischemic stroke treatment.

Tacripyrimidines, the first tacrine-dihydropyrimidine hybrids, as multi-target-directed ligands for Alzheimer's disease

Notwithstanding the combination of cholinesterase (ChE) inhibition and calcium channel blockade within a multitarget therapeutic approach is envisaged as potentially beneficial to confront Alzheimer's disease (AD), this strategy has been scarcely investigated. To explore this promising line, a series of 5-amino-4-aryl-3,4,6,7,8,9-hexahydropyrimido [4,5-b]quinoline-2(1H)-thiones (tacripyrimidines) (4a-l) were designed by juxtaposition of tacrine, a ChE inhibitor (ChEI), and 3,4-dihydropyrimidin-2(1H)-thiones, as efficient calcium channel blockers (CCBs). In agreement with their design, all tacripyrimidines, except the unsubstituted parent compound and its p-methoxy derivative, acted as moderate to potent CCBs with activities generally similar or higher than the reference CCB drug nimodipine and were modest-to-good ChEIs. Most interestingly, the 3'-methoxy derivative (4e) emerged as the first well balanced ChEI/CCB agent, acting as low micromolar hChEI (3.05 μM and 3.19 μM on hAChE and hBuChE, respectively) and moderate CCB (30.4% at 1 μM) with no significant hepatotoxicity toward HepG2 cells and good predicted oral absorption and blood brain barrier permeability.

Quinolinyl Nitrone RP19 Induces Neuroprotection after Transient Brain Ischemia

There is a need to develop additional effective therapies for ischemic stroke. Nitrones, which were first developed as reactive oxygen species (ROS)-trapping compounds, have been proposed as neuroprotective agents for ischemic stroke, a ROS-related disorder. The previous reported ROS-trapping compound, quinolyl nitrone RP19, is here being assayed to induce neuroprotection to ischemia-reperfusion injury in three experimental ischemia models: (i) oxygen-glucose deprivation (OGD) on primary neuronal cultures; (ii) transient global cerebral ischemia in four-vessel occlusion model; and (iii) transient focal cerebral ischemia in middle cerebral artery occlusion (tMCAO) model. RP19 (50 μM) induced long-term neuroprotection at 5 days of recovery after OGD in primary neuronal cultures, evaluated by cell viability assay, and decreased both ROS formation and lipid peroxidation upon recovery after OGD. Furthermore, treatment of animals with RP19 at the onset of reperfusion after either global or focal ischemia, at the dose range that was demonstrated to be neuroprotective in neuronal cultures, decreased neuronal death and apoptosis induction, reduced the size of infarct, and improved the neurological deficit scores after 48 h or 5 days of reperfusion after ischemia. The molecule proposed, quinolyl nitrone RP19, induced substantial neuroprotection on experimental ischemia in neuronal cells, and against ischemic injury following transient brain ischemia in treated animals. This molecule may have potential therapeutic interest in ischemic stroke and to reduce the reoxygenation-induced injury after induced reperfusion.

Multitarget-Directed Ligands Combining Cholinesterase and Monoamine Oxidase Inhibition with Histamine H3 R Antagonism for Neurodegenerative Diseases

The therapy of complex neurodegenerative diseases requires the development of multitarget-directed drugs (MTDs). Novel indole derivatives with inhibitory activity towards acetyl/butyrylcholinesterases and monoamine oxidases A/B as well as the histamine H₃ receptor (H3R) were obtained by optimization of the neuroprotectant ASS234 by incorporating generally accepted H3R pharmacophore motifs. These small-molecule hits demonstrated balanced activities at the targets, mostly in the nanomolar concentration range. Additional in vitro studies showed antioxidative neuroprotective effects as well as the ability to penetrate the blood-brain barrier. With this promising in vitro profile, contilisant (at 1 mg kg^-1 i.p.) also significantly improved lipopolysaccharide-induced cognitive deficits.

5-Methyl-N-(8-(5,6,7,8-tetrahydroacridin-9-ylamino)octyl)-5H-indolo[2,3-b]quinolin-11-amine: a highly potent human cholinesterase inhibitor

The synthesis, cholinesterase inhibition, molecular modelling and ADME properties of novel tacrine-neocryptolepine heterodimers are described. Compound 3 [5-methyl-N-(8-(5,6,7,8-tetrahydroacridin-9-ylamino)octyl)-5H-indolo[2,3-b]quinolin-11-amine], showing a moderate inhibition of the Aβ1-42 self-aggregation (26.5% at a 1 : 5 ratio with Aβ1-42), and a calculated log BB value (0.27) indicating excellent potential BBB penetration, is a highly potent human cholinesterase inhibitor [IC50 (hAChE) = 0.95 ± 0.04 nM; IC50 (hBuChE) = 2.29 ± 0.14 nM] which can be listed among the most potent hAChE inhibitors so far identified, and is not hepatotoxic in vitro at the concentrations at which the ChEs are inhibited. A molecular modeling study was also undertaken in order to elucidate the AChE and the BuChE bind modes of all the new compounds. The docking results show that all of them bind to AChE in extended conformations and to BuChE in folded conformations. Moreover, these studies revealed that the length of the linker is crucial to binding both the catalytic anionic site and the peripheral anionic site.

N-Benzylpiperidine Derivatives as α7 Nicotinic Receptor Antagonists

A series of multitarget directed propargylamines, as well as other differently susbstituted piperidines have been screened as potential modulators of neuronal nicotinic acetylcholine receptors (nAChRs). Most of them showed antagonist actions on α7 nAChRs. Especially, compounds 13, 26, and 38 displayed submicromolar IC50 values on homomeric α7 nAChRs, whereas they were less effective on heteromeric α3β4 and α4β2 nAChRs (up to 20-fold higher IC50 values in the case of 13). Antagonism was concentration dependent and noncompetitive, suggesting that these compounds behave as negative allosteric modulators of nAChRs. Upon the study of a series of less complex derivatives, the N-benzylpiperidine motif, common to these compounds, was found to be the main pharmacophoric group. Thus, 2-(1-benzylpiperidin-4-yl)-ethylamine (48) showed an inhibitory potency comparable to the one of the previous compounds and also a clear preference for α7 nAChRs. In a neuroblastoma cell line, representative compounds 13 and 48 also inhibited, in a concentration-dependent manner, cytosolic Ca(2+) signals mediated by nAChRs. Finally, compounds 38 and 13 inhibited 5-HT3A serotonin receptors whereas they had no effect on α1 glycine receptors. Given the multifactorial nature of many pathologies in which nAChRs are involved, these piperidine antagonists could have a therapeutic potential in cases where cholinergic activity has to be negatively modulated.

Imidazopyranotacrines as Non-Hepatotoxic, Selective Acetylcholinesterase Inhibitors, and Antioxidant Agents for Alzheimer's Disease Therapy

Herein we describe the synthesis and in vitro biological evaluation of thirteen new, racemic, diversely functionalized imidazo pyranotacrines as non-hepatotoxic, multipotent tacrine analogues. Among these compounds, 1-(5-amino-2-methyl-4-(1-methyl-1H-imidazol-2-yl)-6,7,8,9-tetrahydro-4H-pyrano[2,3-b]quinolin-3-yl)ethan-1-one (4) is non-hepatotoxic (cell viability assay on HepG2 cells), a selective but moderately potent EeAChE inhibitor (IC50 = 38.7 ± 1.7 μM), and a very potent antioxidant agent on the basis of the ORAC test (2.31 ± 0.29 μmol·Trolox/μmol compound).

The reaction of 2-amino-4H-pyrans with N-bromosuccinimide

The reaction of racemic 2-amino-4H-pyrans, such as 3-amino-1-aryl-1H-benzo[f]chromene-2-carbonitriles, with N-bromosuccinimide (NBS), in CH2Cl2, at room temperature, is a very quick, regio, stereoselective, and high yielding process, affording major racemic (1S, 2S)-2-bromo-3-imino-benzo[f]chromene or racemic (1S, 2S)-2-bromo-3-(bromoimino)-benzo[f]chromene derivatives, when using 1.0 or 2.2 equivalents of NBS, respectively. This reaction, extended to isomeric 2-amino-4-aryl-4H-benzo[h]chromene-3-carbonitriles, showed an unexpected reactivity, affording racemic (3S,4S)-3-bromo-2-(bromoimino)-benzo[h]chromene-3-carbonitriles or 2-oxo-2H-benzo[h]chromene-3-carbonitriles, when using 2.2 or 1.0 equivalents of NBS, respectively. The reaction of alkyl 6-amino-5-cyano-2-methyl-4H-pyran-3-carboxylates has yielded unstable racemic (3S,4S)-alkyl 3-bromo-2-(bromoimino)-3-cyano-6-methyl-3,4-dihydro-2H-pyran-5-carboxylates. The mechanism of these reactions has been investigated by computational methods.

Multipotent cholinesterase/monoamine oxidase inhibitors for the treatment of Alzheimer's disease: design, synthesis, biochemical evaluation, ADMET, molecular modeling, and QSAR analysis of novel donepezil-pyridyl hybrids

The design, synthesis, and biochemical evaluation of donepezil-pyridyl hybrids (DPHs) as multipotent cholinesterase (ChE) and monoamine oxidase (MAO) inhibitors for the potential treatment of Alzheimer’s disease (AD) is reported. The 3D-quantitative structure-activity relationship study was used to define 3D-pharmacophores for inhibition of MAO A/B, acetylcholinesterase (AChE), and butyrylcholinesterase (BuChE) enzymes and to design DPHs as novel multi-target drug candidates with potential impact in the therapy of AD. DPH14 (Electrophorus electricus AChE [EeAChE]: half maximal inhibitory concentration [IC₅₀] =1.1±0.3 nM; equine butyrylcholinesterase [eqBuChE]: IC₅₀ =600±80 nM) was 318-fold more potent for the inhibition of AChE, and 1.3-fold less potent for the inhibition of BuChE than the reference compound ASS234. DPH14 is a potent human recombinant BuChE (hBuChE) inhibitor, in the same range as DPH12 or DPH16, but 13.1-fold less potent than DPH15 for the inhibition of human recombinant AChE (hAChE). Compared with donepezil, DPH14 is almost equipotent for the inhibition of hAChE, and 8.8-fold more potent for hBuChE. Concerning human monoamine oxidase (hMAO) A inhibition, only DPH9 and 5 proved active, compound DPH9 being the most potent (IC₅₀ [MAO A] =5,700±2,100 nM). For hMAO B, only DPHs 13 and 14 were moderate inhibitors, and compound DPH14 was the most potent (IC₅₀ [MAO B] =3,950±940 nM). Molecular modeling of inhibitor DPH14 within EeAChE showed a binding mode with an extended conformation, interacting simultaneously with both catalytic and peripheral sites of EeAChE thanks to a linker of appropriate length. Absortion, distribution, metabolism, excretion and toxicity analysis showed that structures lacking phenyl-substituent show better druglikeness profiles; in particular, DPHs13–15 showed the most suitable absortion, distribution, metabolism, excretion and toxicity properties. Novel donepezil-pyridyl hybrid DPH14 is a potent, moderately selective hAChE and selective irreversible hMAO B inhibitor which might be considered as a promising compound for further development for the treatment of AD.

N-(furan-2-ylmethyl)-N-methylprop-2-yn-1-amine (F2MPA): A potential cognitive enhancer with MAO inhibitor properties

BACKGROUND

A considerable body of human and animal experimental evidence links monoaminergic systems and cognition. Monoamine oxidase inhibitors (MAOIs), being able to enhance monoaminergic transmission and having neuroprotective properties, might represent a promising therapeutic strategy in cognitive impairment in Alzheimer's disease (AD) and other dementias.

METHODS

The MAO-A and MAO-B inhibition profile of N-(furan-2-ylmethyl)-N-prop-2-yn-1-amine derivates (compounds 1-3) were evaluated by fluorimetric method and their absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties estimated. The effects of the selected compound 1, N-(furan-2-ylmethyl)-N-methylprop-2-yn-1-amine (F2MPA), were evaluated on the basic synaptic transmission, long-term potentiation (LTP), and excitability in the dentate gyrus (DG) of the hippocampus of anesthetized rats.

RESULTS

F2MPA is a partially reversible inhibitor of hMAO-B, with moderate to good ADMET properties and drug-likeness. Intraperitoneal administration of 1 mg/kg F2MPA greatly enhanced basic synaptic transmission, induced LTP, and potentiated electrically induced LTP in the dentate gyrus. Moreover, F2MPA did not modify seizure threshold of pilocarpine-induced convulsion in CD1 mice.

CONCLUSION

Our findings suggest that, the MAO-B inhibitor, F2MPA improves DG synaptic transmission without triggering pathological hyperexcitability. Therefore, F2MPA shows promise as a potential cognition-enhancing therapeutic drug.

Synthesis, pharmacological assessment, and molecular modeling of acetylcholinesterase/butyrylcholinesterase inhibitors: effect against amyloid-β-induced neurotoxicity

The synthesis, molecular modeling, and pharmacological analysis of phenoxyalkylamino-4-phenylnicotinates (2-7), phenoxyalkoxybenzylidenemalononitriles (12, 13), pyridonepezils (14-18), and quinolinodonepezils (19-21) are described. Pyridonepezils 15-18 were found to be selective and moderately potent regarding the inhibition of hAChE, whereas quinolinodonepezils 19-21 were found to be poor inhibitors of hAChE. The most potent and selective hAChE inhibitor was ethyl 6-(4-(1-benzylpiperidin-4-yl)butylamino)-5-cyano-2-methyl-4-phenylnicotinate (18) [IC(50) (hAChE) = 0.25 ± 0.02 μM]. Pyridonepezils 15-18 and quinolinodonepezils 20-21 are more potent selective inhibitors of EeAChE than hAChE. The most potent and selective EeAChE inhibitor was ethyl 6-(2-(1-benzylpiperidin-4-yl)ethylamino)-5-cyano-2-methyl-4-phenylnicotinate (16) [IC(50) (EeAChE) = 0.0167 ± 0.0002 μM], which exhibits the same inhibitory potency as donepezil against hAChE. Compounds 2, 7, 13, 17, 18, 35, and 36 significantly prevented the decrease in cell viability caused by Aβ(1-42). All compounds were effective in preventing the enhancement of AChE activity induced by Aβ(1-42). Compounds 2-7 caused a significant reduction whereas pyridonepezils 17 and 18, and compound 16 also showed some activity. The pyrazolo[3,4-b]quinolines 36 and 38 also prevented the upregulation of AChE induced by Aβ(1-42). Compounds 2, 7, 12, 13, 17, 18, and 36 may act as antagonists of voltage sensitive calcium channels, since they significantly prevented the Ca(2+) influx evoked by KCl depolarization. Docking studies show that compounds 16 and 18 adopted different orientations and conformations inside the active-site gorges of hAChE and hBuChE. The structural and energetic features of the 16-AChE and 18-AChE complexes compared to the 16-BuChE and 18-BuChE complexes account for a higher affinity of the ligand toward AChE. The present data indicate that compounds 2, 7, 17, 18, and 36 may represent attractive multipotent molecules for the potential treatment of Alzheimer's disease.

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.

Α-aryl-N-alkyl nitrones, as potential agents for stroke treatment: synthesis, theoretical calculations, antioxidant, anti-inflammatory, neuroprotective, and brain-blood barrier permeability properties

We report the synthesis, theoretical calculations, the antioxidant, anti-inflammatory, and neuroprotective properties, and the ability to cross the blood-brain barrier (BBB) of (Z)-α-aryl and heteroaryl-N-alkyl nitrones as potential agents for stroke treatment. The majority of nitrones compete with DMSO for hydroxyl radicals, and most of them are potent lipoxygenase inhibitors. Cell viability-related (MTT assay) studies clearly showed that nitrones 1-3 and 10 give rise to significant neuroprotection. When compounds 1-11 were tested for necrotic cell death (LDH release test) nitrones 1-3, 6, 7, and 9 proved to be neuroprotective agents. In vitro evaluation of the BBB penetration of selected nitrones 1, 2, 10, and 11 using the PAMPA-BBB assay showed that all of them cross the BBB. Permeable quinoline nitrones 2 and 3 show potent combined antioxidant and neuroprotective properties and, therefore, can be considered as new lead compounds for further development in specific tests for potential stroke treatment.

Synthesis, biological evaluation, and molecular modeling of donepezil and N-[(5-(benzyloxy)-1-methyl-1H-indol-2-yl)methyl]-N-methylprop-2-yn-1-amine hybrids as new multipotent cholinesterase/monoamine oxidase inhibitors for the treatment of Alzheimer's disease

A new family of multitarget molecules able to interact with acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), as well as with monoamino oxidase (MAO) A and B, has been synthesized. Novel compounds (3-9) have been designed using a conjunctive approach that combines the benzylpiperidine moiety of the AChE inhibitor donepezil (1) and the indolyl propargylamino moiety of the MAO inhibitor N-[(5-benzyloxy-1-methyl-1H-indol-2-yl)methyl]-N-methylprop-2-yn-1-amine (2), connected through an oligomethylene linker. The most promising hybrid (5) is a potent inhibitor of both MAO-A (IC50=5.2±1.1 nM) and MAO-B (IC50=43±8.0 nM) and is a moderately potent inhibitor of AChE (IC50=0.35±0.01 μM) and BuChE (IC50=0.46±0.06 μM). Moreover, molecular modeling and kinetic studies support the dual binding site to AChE, which explains the inhibitory effect exerted on Aβ aggregation. Overall, the results suggest that the new compounds are promising multitarget drug candidates with potential impact for Alzheimer's disease therapy.

Synthesis, analytical features, and biological relevance of 5-(3',4'-dihydroxyphenyl)-γ-valerolactone, a microbial metabolite derived from the catabolism of dietary flavan-3-ols

The physiological significance of 5-(3',4'-dihydroxyphenyl)-γ-valerolactone, an important metabolite derived from the catabolism of flavan-3-ols by gut microbiota, has been often overlooked due to the lack of the commercial standard. In the present work, this metabolite has been chemically synthesized, and its analytical parameters and antioxidant capacity have been determined in comparison to other chemical analogues [isomer 3-(3',4'-dihydroxyphenyl)-δ-valerolactone and γ-valerolactone] and other structurally related compounds [(+)-catechin, (-)-epicatechin, and 3-(3,4-dihydroxyphenyl)-propionic acid]. The synthesized compound was also used to perform a targeted analysis in samples collected during the in vitro fermentation of a grape seed flavan-3-ol extract with human fecal microbiota from three healthy volunteers. The time-course formation of 5-(3',4'-dihydroxyphenyl)-γ-valerolactone revealed large interindividual differences among volunteers, with concentrations ranging from 3.31 to 77.54 μM at 10 h of fermentation. These results are further discussed in view of the scarce reports quantifying 5-(3',4'-dihydroxyphenyl)-γ-valerolactone in in vitro fermentation studies, and pharmacokinetic and intervention studies.

Synthesis and pharmacological assessment of diversely substituted pyrazolo[3,4-b]quinoline, and benzo[b]pyrazolo[4,3-g][1,8]naphthyridine derivatives

The synthesis and pharmacological analyses of a number of pyrazolo[3,4-b]quinoline and benzo[b]pyrazolo[4,3-g][1,8]naphthyridine derivatives are reported. We have synthesized the diversely substituted tacrine analogues 1-6, by Friedländer-type reaction of readily available o-amino-1-methyl-pyrazole-dicarbonitriles with cyclohexanone. The biological evaluation showed that pyrazolotacrines 1-6 are inhibitors of Electrophorus electricus acetylcholinesterase (EeAChE), in the micromolar range, and quite selective in respect to serum horse butyrylcholinesterase (eqBuChE) inhibition; the most interesting inhibitor is N-(5-amino-1-methyl-6,7,8,9-tetrahydro-1H-benzo[b]pyrazolo[4,3-g][1,8]naphthyridin-3-yl)acetamide (5) [IC(50) (EeAChE) = 0.069 ± 0.006 μM; IC(50) (eqBuChE) = 6.3 ± 0.6 μM]. Kinetic studies showed that compound 5 is a mixed-type inhibitor of EeAChE (K(i) = 155 nM). Inhibitor 5 showed a 45% neuroprotection value against rotenone/oligomycin A-induced neuronal death.

Synthesis, structure, theoretical and experimental in vitro antioxidant/pharmacological properties of α-aryl, N-alkyl nitrones, as potential agents for the treatment of cerebral ischemia

The synthesis, structure, theoretical and experimental in vitro antioxidant properties using the DPPH, ORAC, and benzoic acid, as well as preliminary in vitro pharmacological activities of (Z)-α-aryl and heteroaryl N-alkyl-nitrones 6-15, 18, 19, 21, and 23, is reported. In the in vitro antioxidant activity, for the DPPH radical test, only nitrones bearing free phenol groups gave the best RSA (%) values, nitrones 13 and 14 showing the highest values in this assay. In the ORAC analysis, the most potent radical scavenger was nitrone indole 21, followed by the N-benzyl benzene-type nitrones 10 and 15. Interestingly enough, the archetypal nitrone 7 (PBN) gave a low RSA value (1.4%) in the DPPH test, or was inactive in the ORAC assay. Concerning the ability to scavenge the hydroxyl radical, all the nitrones studied proved active in this experiment, showing high values in the 94-97% range, the most potent being nitrone 14. The theoretical calculations for the prediction of the antioxidant power, and the potential of ionization confirm that nitrones 9 and 10 are among the best compounds in electron transfer processes, a result that is also in good agreement with the experimental values in the DPPH assay. The calculated energy values for the reaction of ROS (hydroxyl, peroxyl) with the nitrones predict that the most favourable adduct-spin will take place between nitrones 9, 10, and 21, a fact that would be in agreement with their experimentally observed scavenger ability. The in vitro pharmacological analysis showed that the neuroprotective profile of the target molecules was in general low, with values ranging from 0% to 18.7%, in human neuroblastoma cells stressed with a mixture of rotenone/oligomycin-A, being nitrones 18, and 6-8 the most potent, as they show values in the range 24-18.4%.

Cholinergic and neuroprotective drugs for the treatment of Alzheimer and neuronal vascular diseases. II. Synthesis, biological assessment, and molecular modelling of new tacrine analogues from highly substituted 2-aminopyridine-3-carbonitriles

The synthesis, biological assessment, and molecular modelling of new tacrine analogues 11-22 is described. Compounds 11-22 have been obtained by Friedländer-type reaction of 2-aminopyridine-3-carbonitriles 1-10 with cyclohexanone or 1-benzyl-4-piperidone. The biological evaluation showed that some of these molecules were good AChE inhibitors, in the nanomolar range, and quite selective regarding the inhibition of BuChE, the most potent being 5-amino-2-(dimethylamino)-6,7,8,9-tetrahydrobenzo[1,8-b]-naphthyridine-3-carbonitrile (11) [IC(50) (EeAChE: 14nM); IC(50) (eqBuChE: 5.2μM]. Kinetic studies on the easily available and potent anticholinesterasic compound 5-amino-2-(methoxy)-6,7,8,9-tetrahydrobenzo[1,8-b]-naphthyridine-3-carbonitrile (16) [IC(50) (EeAChE: 64nM); IC(50) (eqBuChE: 9.6μM] showed that this compound is a mixed-type inhibitor (K(i)=69.2nM) of EeAChE. Molecular modelling on inhibitor 16 confirms that this compound, as expected and similarly to tacrine, binds at the catalytic active site of EeAChE. The neuroprotective profile of molecules 11-22 has been investigated in SH-SY5Y neuroblastoma cells stressed with a mixture of oligomycin-A/rotenone. Compound 16 was also able to rescue by 50% cell death induced by okadaic acid in SH-SY5Y cells. From these results we conclude that the neuroprotective profile of these molecules is moderate, the most potent being compounds 12 and 17 which reduced cell death by 29%. Compound 16 does not affect ACh- nor K(+)-induced calcium signals in bovine chromaffin cells. Consequently, tacrine analogues 11-22 can be considered attractive therapeutic molecules on two key pharmacological targets playing key roles in the progression of Alzheimer, that is, cholinergic dysfunction and oxidative stress, as well as in neuronal cerebrovascular diseases.