Synthesis, biological evaluation and molecular modelling of diversely functionalized heterocyclic derivatives as inhibitors of acetylcholinesterase/butyrylcholinesterase and modulators of Ca2+ channels and nicotinic receptors

Facile synthesis of novel tacrine analogues

The synthesis of highly potent and selective acetylcholinesterase inhibitors, tacrine analogues with the structure of fused 4-aminoquinolines and 4-aminopyridines, has been accomplished by direct cyclocondensation of 1-aryl-4-cyano-5-aminopyrazoles with cyclic ketones using tin(IV) chloride as catalyst.

Conjugated imines and iminium salts as versatile acceptors of nucleophiles

Growing interests in nitrogen-containing molecules involving bioactive and functional materials have stimulated the recent development of synthetic methodologies where nucleophilic addition reactions to imino carbons are utilized in crucial steps. This article summarizes double nucleophilic addition reactions with alpha,beta-unsaturated aldimines, addition reactions using alkynyl imines, "umpoled" reactions of alpha-imino esters, and the use of iminium salts as reactive electrophiles.

Modeling of acetylcholinesterase inhibition by tacrine analogues using Bayesian-regularized Genetic Neural Networks and ensemble averaging

Acetylcholinesterase inhibition was modeled for a set of 136 tacrine analogues using Bayesian-regularized Genetic Neural Networks (BRGNNs). In the BRGNN approach the Bayesian-regularization avoids overtraining/overfitting and the genetic algorithm (GA) allows exploring an ample pool of 3D-descriptors. The predictive capacity of our selected model was evaluated by averaging multiple validation sets generated as members of diverse-training set neural network ensembles (NNEs). The ensemble averaging provides reliable statistics. When 40 members are assembled, the NNE provides a reliable measure of training and test set R values of 0.921 and 0.851 respectively. In other respects, the ability of the nonlinear selected GA space for differentiating the data was evidenced when the total data set was well distributed in a Kohonen Self-Organizing Map (SOM). The location of the inhibitors in the map facilitates the analysis of the connection between compounds and serves as a useful tool for qualitative predictions.

Multifunctional neuroprotective drugs targeting monoamine oxidase inhibition, iron chelation, adenosine receptors, and cholinergic and glutamatergic action for neurodegenerative diseases

A new paradigm is emerging in the targeting of multiple disease aetiologies that collectively lead to neurodegenerative disorders such as Parkinson's disease, Alzheimer's disease, post-stroke neurodegeneration and others. This paradigm challenges the widely held assumption that 'silver bullet' agents are superior to 'dirty drugs' when it comes to drug therapy. Accumulating evidence in the literature suggests that many neurodegenerative diseases have multiple mechanisms in their aetiologies, thus suggesting that a drug with at least two mechanisms of action targeted at multiple aetiologies of the same disease may offer more therapeutic benefit in certain disorders compared with a drug that only targets one disease aetiology. This review offers a synopsis of therapeutic strategies and novel investigative drugs developed in the authors' own and other laboratories that modulate multiple disease targets associated with neurodegenerative diseases.

Quantitative structure–activity relationship (QSAR) of tacrine derivatives against acetylcholinesterase (AChE) activity using variable selections

A diverse approach to the quantitative structure-activity relationship (QSAR) of tacrine derivatives against acetylcholinesterase (AChE) activity was studied using variable selections of stepwise multiple linear regression (MLR), genetic algorithm (GA)-MLR, and simulated annealing (SA)-MLR. AChE activity (logRA) of tacrine derivatives was expressed with acceptable explanation (95.5-95.9%) and good predictive power (94.5-95.2%), respectively, in the models. The best equation was obtained from simulated annealing (SA) MLR with greater explanatory capability and better prediction, with a smaller standard error than other methods. The resulting models with the given descriptors illustrate the significant roles of hydrophobic and electrostatic interaction on increasing AChE activity, but hydrophilic and topological feature of molecules were shown to decrease AChE activity.

Synthesis of substituted 4-azaisoindoles — New tacrine analogues

The regioselective Friedländer reaction of 3-amino-4-cyanopyrroles with a series of cyclic ketones has enabled the first reported synthesis of substituted 4-azaisoindoles. Structurally, this new class of compounds stands for the first reported 4-azaisoindole tacrine analogues. A reaction mechanism for the formation of the reported 4-azaisoindoles is proposed.Key words: 4-azaisoindoles, tacrine, Friedländer reaction, pyrroles, mechanism.

Synthesis and biological evaluation of new 4H-pyrano[2,3-b]quinoline derivatives that block acetylcholinesterase and cell calcium signals, and cause neuroprotection against calcium overload and free radicals

The synthesis and biological evaluation of ethyl 5-amino-4-(3-pyridyl)-2-methyl-6,7,8,9-tetrahydro-4H-pyrano[2,3-b]quinoline-3-carboxylates (9-11) is described. We have found that these compounds inhibit AChE with a mild potency, mitigates the [Ca(2+)](c) triggered by high K(+), and cause neuroprotection against Ca(2+) overloading and free radical-induced neuronal death.

New multipotent tetracyclic tacrines with neuroprotective activity

The synthesis and the biological evaluation (neuroprotection, voltage dependent calcium channel blockade, AChE/BuChE inhibitory activity and propidium binding) of new multipotent tetracyclic tacrine analogues (5-13) are described. Compounds 7, 8 and 11 showed a significant neuroprotective effect on neuroblastoma cells subjected to Ca(2+) overload or free radical induced toxicity. These compounds are modest AChE inhibitors [the best inhibitor (11) is 50-fold less potent than tacrine], but proved to be very selective, as for most of them no BuChE inhibition was observed. In addition, the propidium displacement experiments showed that these compounds bind AChE to the peripheral anionic site (PAS) of AChE and, consequently, are potential agents that can prevent the aggregation of beta-amyloid. Overall, compound 8 is a modest and selective AChE inhibitor, but an efficient neuroprotective agent against 70mM K(+) and 60microM H(2)O(2). Based on these results, some of these molecules can be considered as lead candidates for the further development of anti-Alzheimer drugs.

Synthesis, acetylcholinesterase inhibition and neuroprotective activity of new tacrine analogues

The synthesis and the biological evaluation (acetylcholinesterase inhibition activity and neuroprotection) of the new tacrine analogues 2-14 is described.

Synthesis and evaluation of tacrine–E2020 hybrids as acetylcholinesterase inhibitors for the treatment of Alzheimer’s disease

Tacrine-E2020 hybrids and some related compounds were prepared and their bioactivities on the Alzheimer's disease were assayed. The optimum hybrid inhibitor 3 is 37-fold more potent and 31-fold more selective than tacrine in vitro.