E. Gálvez

Structural and conformational study of diazabicyclanones and diazabicyclanols

Abstract 3-Methyl-7-alkyl-3,7-diazabicyclo [3.3.1] nonan-9-ones and 9-ols have been studied by 1 H, 13 C NMF_IR and Raman spectroscopy and the crystal structure of 3,7-dimethyl-3,7-diazabicyclo[8.3.1] nonan-9-ol has been determined by X-ray diffraction. The ketones studied adopt in CDCl 3 and (CD 3 ) 2 SO solution a flattened chair—chair conformation; however, in the crystalline N -methyl N -benzyl derivative, the bicyclic system adopts a chair—boat conformation. X-ray data for 3,7-dimethyl-3,7-diazabicyclo [3.3.1] nonan-9-ol have revealed that the compound has crystallized in a chair—chair conformation stabilized by water and ethanol molecules. Frc.a IR data the existence of another chair anhydrous crystalline form stabilized by intramolecular hydrogen bonding has been deduced. The preferred conformation in solution of the diazabycyclanols mainly depends on the polarity of the solvent.

Synthesis, Inhibitory Activity of Cholinesterases, and Neuroprotective Profile of Novel 1,8-Naphthyridine Derivatives

1,8-Naphthyridine derivatives related to 17 (ITH4012), a neuroprotective compound reported by our research group, have been synthesized. In general, they have shown better inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) than most tacrine derivatives previously synthesized in our laboratory. The compounds presented an interesting neuroprotective profile in SH-SY5Y neuroblastoma cells stressed with rotenone/oligomycin A. Moreover, compound 14 (ethyl 5-amino-2-methyl-6,7,8,9-tetrahydrobenzo[b][1,8]naphthyridine-3-carboxylate) also caused protection in cells stressed with okadaic acid (OA) or amyloid beta 1-42 peptide (Abeta(1-42)). Interestingly, compound 14 prevented the OA-induced PP2A inhibition, one of the enzymes implicated in tau dephosphorylation. This compound also exhibited neuroprotection against neurotoxicity elicited by oxygen and glucose deprivation in hippocampal slices. Because these stressors caused neuronal damage related to physiopathological hallmarks found in the brain of Alzheimers disease (AD) patients, we conclude that compound 14 deserves further in vivo studies in AD models to test its therapeutic potential in this disease.

Flecainide increases Kir2.1 currents by interacting with cysteine 311, decreasing the polyamine-induced rectification

Both increase and decrease of cardiac inward rectifier current (IK1) are associated with severe cardiac arrhythmias. Flecainide, a widely used antiarrhythmic drug, exhibits ventricular proarrhythmic effects while effectively controlling ventricular arrhythmias associated with mutations in the gene encoding Kir2.1 channels that decrease IK1 (Andersen syndrome). Here we characterize the electrophysiological and molecular basis of the flecainide-induced increase of the current generated by Kir2.1 channels (IKir2.1) and IK1 recorded in ventricular myocytes. Flecainide increases outward IKir2.1 generated by homotetrameric Kir2.1 channels by decreasing their affinity for intracellular polyamines, which reduces the inward rectification of the current. Flecainide interacts with the HI loop of the cytoplasmic domain of the channel, Cys311 being critical for the effect. This explains why flecainide does not increase IKir2.2 and IKir2.3, because Kir2.2 and Kir2.3 channels do not exhibit a Cys residue at the equivalent position. We further show that incubation with flecainide increases expression of functional Kir2.1 channels in the membrane, an effect also determined by Cys311. Indeed, flecainide pharmacologically rescues R67W, but not R218W, channel mutations found in Andersen syndrome patients. Moreover, our findings provide noteworthy clues about the structural determinants of the C terminus cytoplasmic domain of Kir2.1 channels involved in the control of gating and rectification.

Synthesis, biological assessment and molecular modeling of new multipotent MAO and cholinesterase inhibitors as potential drugs for the treatment of Alzheimer’s disease

The synthesis, biological evaluation and molecular modeling of new multipotent inhibitors of type I and type II, able to simultaneously inhibit monoamine oxidases (MAO) as well as acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), is described. Compounds of type I were prepared by sequential reaction of 2,6-dichloro-4-phenylpyridine-3,5-dicarbonitrile (14) [or 2,6-dichloropyridine-3,5-dicarbonitrile (15)] with prop-2-yn-1-amine (or N-methylprop-2-yn-1-amine) and 2-(1-benzyl-piperidin-4-yl)alkylamines 22-25. Compounds of type II were prepared by Friedländer type reaction of 6-amino-5-formyl-2-(methyl(prop-2-yn-1-yl)amino)nicotinonitriles 32 and 33 with 4-(1-benzylpiperidin-4-yl)butan-2-one (31). The biological evaluation of molecules 1-11 showed that most of these compounds are potent, in the nanomolar range, and selective AChEI, with moderate and equipotent selectivity for MAO-A and MAO-B inhibition. Kinetic studies of compound 8 proved that this is a EeAChE mixed type inhibitor (IC(50) = 16 ± 2; Ki = 12 ± 3 nM). Molecular modeling investigation on compound 8 confirmed its dual AChE inhibitory profile, binding simultaneously at the catalytic active site (CAS) and at the peripheric anionic site (PAS). In overall, compound 11, as a potent and selective dual AChEI, showing a moderate and selective MAO-A inhibitory profile, can be considered as an attractive multipotent drug for further development on two key pharmacological targets playing key roles in the therapy of Alzheimers disease.

Structural and conformational study of 3-phenethyl-3-azabicyclo[3.2.1] octan-8-β-ol

Abstract The infrared and 1 H and 13 C NMR spectra of 3-aza-bicyclo[3.2.1]octane-8-β-ol have been examined in several media. To assist in interpretation of the spectroscopic data, the crystal structure has been determined by X-ray diffraction. The bicyclic system adopts a chair—envelope conformation with OH and phenethyl groups, respectively, in axial and equatorial positions with respect to the piperidine ring. The crystal structure is stabilized by means of OH…N intermolecular hydrogen bonding. In CCl 4 solution the initial chair—envelope conformation changes to a boat—envelope conformation which is stabilized by an intramolecular hydrogen bond. The unambiguous assignment of all protons of the bicyclic system, not previously described, has also been carried out.

Conformational study of N-substituted 8-azabicyclo[3.2.1]octan-3-ones

Abstract N-Substituted 8-azabicyclo[3.2.1]octan-3-ones have been studied by 1H and 13C NMR spectroscopy. In CDCl3 solutions, these ketones display the same preferred conformation. The pyrrolidine and piperidone rings adopt a flattened N-8 envelope and distorted chair conformation, puckered at N-8 and flattened at C-3, respectively, with the N-substituent in axial position with respect to the piperidone ring.

Structural and conformational study of 3,7-disubstituted 3,7-diazabicyclo[3.3.1]nonan-9-ones

Abstract 3-Alkyl-7-methyl-3,7-diazabicyclo[3.3.1]nonan-9-ones have been studied by 1 H- and 13 C-NMR spectroscopy. In CDCl 3 solutions, these ketones adopt a flattened chair—chair conformation with the N-substituents in the equatorial position. From the smallest (R = CH 3 ) to the largest (R = CH(CH 3 ) 2 ) substituent, an increase of the distortion for the N -alkylated piperidone ring is observed.

Synthesis and biological assessment of diversely substituted furo[2,3-b]quinolin-4-amine and pyrrolo[2,3-b]quinolin-4-amine derivatives, as novel tacrine analogues ☆

The synthesis and pharmacological analyses of a number of furo[2,3-b]quinolin-4-amine, and pyrrolo[2,3-b]quinolin-4-amine derivatives are reported. Thus, we synthesized diversely substituted tacrine analogues 1-11 and 12-16 by Friedländer-type reaction of readily available o-amino(furano/pyrrolo)nitriles with suitable and selected cycloalkanones. The biological evaluation of furanotacrines1-11 and pyrrolotacrine13 showed that these are good, in the micromolar range, and highly selective inhibitors of BuChE. In the furanotacrine group, the most interesting inhibitor was 2-(p-tolyl)-5,6,7,8-tetrahydrofuro[2,3-b]quinolin-4-amine (3) [IC(50) (eqBuChE)=2.9 ± 0.4 μM; IC(50) (hBuChE)=119 ± 15 μM]. Conversely, pyrrolotacrines 12 and 14 proved moderately equipotent for both cholinesterases, being 1,2-diphenyl-5,6,7,8-tetrahydro-1H-pyrrolo[2,3-b]quinolin-4-amine (12) the most potent for the inhibition of both enzymes [IC(50) (EeAChE)=0.61 ± 0.04 μM; IC(50) (eqBuChE)=0.074 ± 0.009 μM]. Moreover, pyrrolotacrine 12, at concentrations as low as 300 nM can afford significant neuroprotective effects against Aβ-induced toxicity. Docking studies show that compounds 3 and 12 bind in the middle of the AChE active site gorge, but are buried deeper inside BuChE active site gorge, as a consequence of larger BuChE gorge void. All these data suggest that these new tacrine analogues could be used for the potential treatment of Alzheimers disease.

Chemical and Pharmacological Studies on Enantiomerically Pure p-Methoxytacripyrines, Promising Multi-Target-Directed Ligands for the Treatment of Alzheimer’s Disease

Alzheimer’s disease (AD) is an age-related neurodegenerative process characterized by progressive memory loss and other cognitive impairments. Although the etiology of AD is not well known, several factors such as amyloid-b (Ab) deposits, t-protein aggregation, oxidative stress or low levels of acetylcholine are thought to play significant roles in the pathophysiology of the disease. In spite of the continuous efforts of the pharmaceutical industry and academia, an efficient strategy for the treatment of AD is still lacking. This is partially related to the complexity of the pathology, in which multiple factors contribute to the final scenario. The multifactorial nature of AD has given rise to the rational basis for the development of the most current innovative therapeutic approaches based on the “one molecule, multiple targets” paradigm. The multitarget approach has been widely explored leading to the development of several multi-target-direct ligands (MTDLs), which include novel tacrine–melatonin hybrids, dual inhibitors of acetylcholinesterase (AChE) and monoamine oxidase, or serotonin transporters, potent cholinesterase inhibitors with antioxidant and neuroprotective properties, gallamine–tacrine hybrids binding at cholinesterases and M2 muscarinic receptors, or NO-donor–tacrine hybrids as hepatoprotective anti-AD drugs. Based on the multitarget approach, some years ago we designed and synthesized novel multipotent molecules, called tacripyrines (I), by combination of tacrine and nimodipine, as reference agents with a multipotent cholinergic and calcium antagonism profile, respectively, for the treatment of AD. 18] Racemic tacripyrines exhibited potent and selective AChE inhibition, high calcium-channel blocking activity, as well as neuroprotective/antioxidant properties, able to cross the blood– brain barrier. Particularly, (R/S)-p-methoxytacripyrine (ethyl 5-amino-4-(4methoxyphenyl)-2-methyl-1,4,6,7,8,9-hexahydrobenzo[b][1,8] naphthyridine-3-carboxylate; (R/S)-1), one of the most potent cholinergic tacripyrines (IC50 = 105 15 nm against human AChE), at 100 mm showed 30.7 8.6 % inhibition of the pro-aggregating action of AChE on Ab peptide (230 mm) ; furthermore, (R/S)-1 was also a moderate inhibitor of b-amyloid selfaggregation (34.9 5.4 % at [I] = 50 mm). Overall, these results prompted us to consider 1 as an appropriate hit compound in this project, and consequently, to undertake the pharmacological analysis of both enantiomers. The detailed investigation of chiral discrimination has enormous importance in medicinal chemistry as a means to better elucidating the mechanisms of interaction and to identify structural features involved in ligand–target recognition. The synthesis of (R/S)-1 was scaled up for this study, but essentially followed the general protocol previously described. Briefly, starting from a mixture of E/Z-isomers of ethyl 2-(4-methoxybenzylidene)-3-oxobutanoate (2), and reacting it with [a] Dr. M. Bartolini, Dr. M. Pistolozzi, Prof. V. Andrisano Department of Pharmaceutical Sciences, University of Bologna Via Belmeloro 6, 40126 Bologna (Italy) Fax: (+ 39) 051-2099734 E-mail : manuela.bartolini3@unibo.it

Synthesis and structural and conformational study of some amines derived from the norgranatane system

Abstract A series of N -substituted-9-phenethyl-3-amino norgranatane derivatives have been synthesized and studied by 1 H and 13 C NMR spectroscopy. The compounds studied display in deuterochloroform the same preferred flattened chair-boat conformation with the disubstituted ring in a slightly distorted boat form. The arylamino groups, in the C-3α position lie in the symmetry plane with respect to the bicyclic system.