Carlo Matera

Epiboxidine and novel-related analogues : A convenient synthetic approach and estimation of their affinity at neuronal nicotinic acetylcholine receptor subtypes

Racemic exo-epiboxidine 3, endo-epiboxidine 6, and the two unsaturated epiboxidine-related derivatives 7 and 8 were efficiently prepared taking advantage of a palladium-catalyzed Stille coupling as the key step in the reaction sequence. The target compounds were assayed for their binding affinity at neuronal alpha4beta2 and alpha7 nicotinic acetylcholine receptors. Epiboxidine 3 behaved as a high affinity alpha4beta2 ligand (K(i)=0.4 nM) and, interestingly, evidenced a relevant affinity also for the alpha7 subtype (K(i)=6 nM). Derivative 7, the closest analogue of 3 in this group, bound with lower affinity at both receptor subtypes (K(i)=50 nM for alpha4beta2 and K(i)=1.6 microM for alpha7) evidenced a gain in the alpha4beta2 versus alpha7 selectivity when compared with the model compound.

Design, synthesis, and pharmacological characterization of novel spirocyclic quinuclidinyl-Δ2-isoxazoline derivatives as potent and selective agonists of α7 nicotinic acetylcholine receptors.

A set of racemic spirocyclic quinuclidinyl‐Δ2‐isoxazoline derivatives was synthesized using a 1,3‐dipolar cycloaddition‐based approach. Target compounds were assayed for binding affinity toward rat neuronal homomeric (α7) and heteromeric (α4β2) nicotinic acetylcholine receptors. Δ2‐Isoxazolines 3 a (3‐Br), 6 a (3‐OMe), 5 a (3‐Ph), 8 a (3‐OnPr), and 4 a (3‐Me) were the ligands with the highest affinity for the α7 subtype (Ki values equal to 13.5, 14.2, 25.0, 71.6, and 96.2 nM, respectively), and showed excellent α7 versus α4β2 subtype selectivity. These compounds, tested in electrophysiological experiments against human α7 and α4β2 receptors stably expressed in cell lines, behaved as partial α7 agonists with varying levels of potency. The two enantiomers of (±)‐3‐methoxy‐1‐oxa‐2,7‐diaza‐7,10‐ethanospiro[4.5]dec‐2‐ene sesquifumarate 6 a were prepared using (+)‐dibenzoyl‐L‐ or (−)‐dibenzoyl‐D‐tartaric acid as resolving agents. Enantiomer (R)‐(−)‐6 a was found to be the eutomer, with Ki values of 4.6 and 48.7 nM against rat and human α7 receptors, respectively.

Design of novel α7-subtype-preferring nicotinic acetylcholine receptor agonists: Application of docking and MM-PBSA computational approaches, synthetic and pharmacological studies

In the search for nicotinic acetylcholine receptor (nAChRs) agonists with a selective affinity for the homomeric alpha7 channels, we carried out the virtual screening of a test set of potential nicotinic ligands, and adopted a simplified MM-PBSA approach to estimate their relative binding free energy values. By means of this procedure, previously validated by a training set of compounds, we reached a realistic compromise between computational accuracy and calculation rate, and singled out a small group of novel structurally related derivatives characterized by a promising theoretical affinity for the alpha7 subtype. Among them, five new compounds were synthesized and assayed in binding experiments at neuronal alpha7 as well as alpha4beta2 nAChRs.

Bis(ammonio)alkane-type agonists of muscarinic acetylcholine receptors: Synthesis, in vitro functional characterization, and in vivo evaluation of their analgesic activity

In this study, we synthesized and tested in vitro and in vivo two groups of bis(ammonio)alkane-type compounds, 6a-9a and 6b-9b, which incorporate the orthosteric muscarinic agonist iperoxo into a molecular fragment of the M2-selective allosteric modulators W84 and naphmethonium. The agonist potency and efficacy of these hybrid derivatives at M1, M2 and M3 muscarinic receptor subtypes and their anticholinesterase activity were evaluated on isolated tissue preparations. Their analgesic action was then assayed in vivo in the acetic acid writhing test and the occurrence of peripheral and central cholinergic side effects was also determined. The investigated hybrids behaved as potent muscarinic agonists and weak cholinesterase inhibitors. These effects were more pronounced for bisquaternary salts bearing the naphmethonium moiety than for the W84-containing analogs, and resulted in a significant analgesic activity in vivo. A promising profile was displayed by the naphmethonium-related compound 8b, which combined the most potent antinociception among the test compounds with the absence of relevant cholinergic side effects.

Pharmacological approaches to targeting muscarinic acetylcholine receptors.

The presence of cholinergic system markers and muscarinic receptor subtypes in several tissues also of nonneuronal type has been largely demonstrated. Acetylcholine, synthesized in the nervous system, can locally contribute to modulate cell proliferation, survival and apoptosis. Considering that the cholinergic system functions are impaired in a number of disorders, the identification of new drugs regulating these functions appears of great clinical relevance. The possible involvement of muscarinic acetylcholine receptors in different pathologies has been proposed in recent years and is becoming an important area of study. However, the lack of selective muscarinic receptor ligands has for long time limited the therapeutic treatment based on muscarinic receptors as targets. To date, some muscarinic ligands such as xanomeline (patent, US5980933) or cevimeline (patents US4855290, US5571918) have been developed for the treatment of several pathologies (Alzheimers and Sjogrens diseases). The present review will be focused on the potential effects produced by muscarinic receptor activation in different pathologies, including tumors. In fact, the potential use of muscarinic ligands in therapeutic protocols in cancer therapy will be discussed, considering that several muscarinic antagonists, already used in the treatment of genitourinary diseases (e.g. darifenacin, patent, US5096890, US6106864), have also been demonstrated to arrest the tumor growth in vivo. Moreover, the contribution of muscarinic receptors to analgesia is also reviewed. Finally, some of the most significant achievements in the field of bitopic/dualsteric ligands will be discussed and the molecules patented so far will be presented.

Ligand Binding Ensembles Determine Graded Agonist Efficacies at a G Protein-Coupled Receptor

G protein-coupled receptors constitute the largest family of membrane receptors and modulate almost every physiological process in humans. Binding of agonists to G protein-coupled receptors induces a shift from inactive to active receptor conformations. Biophysical studies of the dynamic equilibrium of receptors suggest that a portion of receptors can remain in inactive states even in the presence of saturating concentrations of agonist and G protein mimetic. However, the molecular details of agonist-bound inactive receptors are poorly understood. Here we use the model of bitopic orthosteric/allosteric (i.e. dualsteric) agonists for muscarinic M2 receptors to demonstrate the existence and function of such inactive agonist·receptor complexes on a molecular level. Using all-atom molecular dynamics simulations, dynophores (i.e. a combination of static three-dimensional pharmacophores and molecular dynamics-based conformational sampling), ligand design, and receptor mutagenesis, we show that inactive agonist·receptor complexes can result from agonist binding to the allosteric vestibule alone, whereas the dualsteric binding mode produces active receptors. Each agonist forms a distinct ligand binding ensemble, and different agonist efficacies depend on the fraction of purely allosteric (i.e. inactive) versus dualsteric (i.e. active) binding modes. We propose that this concept may explain why agonist·receptor complexes can be inactive and that adopting multiple binding modes may be generalized also to small agonists where binding modes will be only subtly different and confined to only one binding site.

Novel tricyclic Δ2-isoxazoline and 3-oxo-2-methyl-isoxazolidine derivatives: Synthesis and binding affinity at neuronal nicotinic acetylcholine receptor subtypes

A group of novel tricyclic Delta(2)-isoxazolines (4b, 5b, 7a-b, and 8a-b) and 3-oxo-isoxazolidines (6a-b and 9a-b), structurally related to cytisine or norferruginine, was prepared through 1,3-dipolar cycloadditions involving suitable olefins and bromonitrile oxide. The target compounds were assayed at alpha4beta2 and alpha7 neuronal acetylcholine receptors (nAChRs). The results of competition binding experiments indicated for the new derivatives a reduction of the affinity at the alpha4beta2 subtype in comparison with the reference molecules, coupled with an overall negligible affinity at the alpha7 subtype. The binding mode of the bromo-Delta(2)-isoxazolines 4b and 7b, which were the highest affinity ligands in the series (K(i)=0.92 and 0.75 microM, respectively), was analyzed by applying a recently developed model of the alpha4beta2 nAChRs.

On the selection of an opioid for local skin analgesia: Structure-skin permeability relationships

Recent studies demonstrated that post-herpetical and inflammatory pain can be locally managed by morphine gels, empirically chosen. Aiming to rationalize the selection of the most suitable opioid for the cutaneous delivery, we studied the in vitro penetration through human epidermis of eight opioids, evidencing the critical modifications of the morphinan core. Log P, log D, solid-state features and solubility were determined. Docking simulations were performed using supramolecular assembly made of ceramide VI. The modifications on position 3 of the morphinan core resulted the most relevant in determining both physicochemical characteristics and diffusion pattern. The 3-methoxy group weakened the cohesiveness of the crystal lattice structure and increased the permeation flux (J). Computational studies emphasized that, while permeation is essentially controlled by molecule apolarity, skin retention depends on a fine balance of polar and apolar molecular features. Moreover, ChemPLP scoring the interactions between the opioids and ceramide, correlated with both the amount retained into the epidermis (Qret) and J. The balance of the skin penetration properties and the affinity potency for μ-receptors evidenced hydromorphone as the most suitable compound for the induction of local analgesia.

Bifunctional compounds targeting both D2 and non-α7 nACh receptors: design, synthesis and pharmacological characterization.

We designed, prepared and tested a set of structural analogs 1-4 as new hybrid compounds by incorporating, through a common alkyl chain of variable length, the pharmacophoric elements of N-n-alkyl nicotinium salts (non-α7 nicotinic acetylcholine receptors antagonists) and of 7-hydroxy-2-(aminomethyl)chromanes (dopaminergic D2 receptor agonists). The target compounds, which were assayed in binding experiments and electrophysiological, functional and Erk1/2 activation tests, essentially combined the pharmacological profiles of their individual receptor ligands. Among the studied derivatives, hybrid 2, one of the shortest homologs, in addition to the antagonist nicotinic profile similar to the other three congeners, behaved as a high affinity ligand at the investigated heteromeric nAChRs and as a low efficacy agonist at D2Rs. These bifunctional derivatives represent novel pharmacological tools in the study of nicotine addiction.

Synthesis and binding affinity at α4β2 and α7 nicotinic acetylcholine receptors of new analogs of epibatidine and epiboxidine containing the 7-azabicyclo[2.2.1]hept-2-ene ring system.

A group of novel racemic nicotinic ligands structurally related to epibatidine or epiboxidine [(±)-10-(±)-17] was synthesized through a palladium-catalyzed cross-coupling between the appropriate vinyl triflate and a range of organometallic heterocycles. The target compounds were evaluated for binding affinity at the α4β2 and α7 neuronal nicotinic receptors (nAChRs). The set of 3-pyridinyl derivatives (±)-10, (±)-11 and (±)-12 exhibited an affinity for the α4β2 nAChR subtype in the subnanomolar range (K(i) values of 0.20, 0.40 and 0.50nM, respectively) and behaved as α4β2 versus α7 subtype selective ligands. Interestingly, the epiboxidine-related dimethylammonium iodide (±)-17, which retained a good affinity for the α4β2 nAChR (K(i)=13.30nM), tightly bound also to the α7 subtype (K(i)=1.60nM), thus displaying a reversal of the affinity trend among the reference and new nicotinic ligands under investigation.