Modification of the anabaseine pyridine nucleus allows achieving binding and functional selectivity for the α3β4 nicotinic acetylcholine receptor subtype

Synthesis of Azabicyclo[3.1.1]heptenes Enabled by Catalyst-Controlled Annulations of Bicyclo[1.1.0]butanes with Vinyl Azides

Bridged bicyclic scaffolds are emerging bioisosteres of planar aromatic rings under the concept of "escape from flatland". However, adopting this concept into the exploration of bioisosteres of pyridines remains elusive due to the challenge of incorporating a N atom into such bridged bicyclic structures. Herein, we report practical routes for the divergent synthesis of 2- and 3-azabicyclo[3.1.1]heptenes (aza-BCHepes) as potential bioisosteres of pyridines from the readily accessible vinyl azides and bicyclo[1.1.0]butanes (BCBs) via two distinct catalytic annulations. The reactivity of vinyl azides tailored with BCBs is the key to achieving divergent transformations. TiIII-catalyzed single-electron reductive generation of C-radicals from BCBs allows a concise (3 + 3) annulation with vinyl azides, affording novel 2-aza-BCHepe scaffolds. In contrast, scandium catalysis enables an efficient dipolar (3 + 2) annulation with vinyl azides to generate 2-azidobicyclo[2.1.1]hexanes, which subsequently undergo a chemoselective rearrangement to construct 3-aza-BCHepes. Both approaches efficiently deliver unique azabicyclo[3.1.1]heptene scaffolds with a high functional group tolerance. The synthetic utility has been further demonstrated by scale-up reactions and diverse postcatalytic transformations, providing valuable azabicyclics including 2- and 3-azabicyclo[3.1.1]heptanes and rigid bicyclic amino esters. In addition, the related sp2-hybridized nitrogen atom and the similar geometric property between pyridines and corresponding aza-BCHepes indicate that they are promising bioisosteres of pyridines.

Marine Origin Ligands of Nicotinic Receptors: Low Molecular Compounds, Peptides and Proteins for Fundamental Research and Practical Applications

The purpose of our review is to briefly show what different compounds of marine origin, from low molecular weight ones to peptides and proteins, offer for understanding the structure and mechanism of action of nicotinic acetylcholine receptors (nAChRs) and for finding novel drugs to combat the diseases where nAChRs may be involved. The importance of the mentioned classes of ligands has changed with time; a protein from the marine snake venom was the first excellent tool to characterize the muscle-type nAChRs from the electric ray, while at present, muscle and α7 receptors are labeled with the radioactive or fluorescent derivatives prepared from α-bungarotoxin isolated from the many-banded krait. The most sophisticated instruments to distinguish muscle from neuronal nAChRs, and especially distinct subtypes within the latter, are α-conotoxins. Such information is crucial for fundamental studies on the nAChR revealing the properties of their orthosteric and allosteric binding sites and mechanisms of the channel opening and closure. Similar data are provided by low-molecular weight compounds of marine origin, but here the main purpose is drug design. In our review we tried to show what has been obtained in the last decade when the listed classes of compounds were used in the nAChR research, applying computer modeling, synthetic analogues and receptor mutants, X-ray and electron-microscopy analyses of complexes with the nAChRs, and their models which are acetylcholine-binding proteins and heterologously-expressed ligand-binding domains.

Design, synthesis, and electrophysiological evaluation of NS6740 derivatives: Exploration of the structure-activity relationship for alpha7 nicotinic acetylcholine receptor silent activation

The α7 nicotinic acetylcholine receptor (nAChR) silent agonists, able to induce receptor desensitization and promote the α7 metabotropic function, are emerging as new promising therapeutic anti-inflammatory agents. Herein, we report the structure-activity relationship investigation of the archetypal silent agonist NS6740 (1,4-diazabicyclo[3.2.2]nonan-4-yl(5-(3-(trifluoromethyl)-phenyl)-furan-2-yl)methanone) (1) to elucidate the ligand-receptor interactions responsible for the α7 silent activation. In this study, NS6740 fragments 11-16 and analogs 17-32 were designed, synthesized, and assayed on human α7 nAChRs expressed in Xenopus laevis oocytes with two-electrode voltage clamping experiments. All together the structural portions of NS6740 were critical to engender its peculiar activity profile. The diazabicyclic nucleus was essential but not sufficient for inducing α7 silent activation. The central hydrogen-bond acceptor core and the aromatic moiety were crucial for promoting prolonged α7 receptor binding and sustained desensitization. Compounds 13 and 17 were efficacious partial agonists. Compounds 12, 21, 23-26, and 30 strongly desensitized α7 nAChR and therefore may be of interest for additional investigation of inflammation responses. We gained key structural information useful for further silent agonist development.

ICH3, a selective alpha7 nicotinic acetylcholine receptor agonist, modulates adipocyte inflammation associated with obesity

PURPOSE

The alpha7 nicotinic acetylcholine receptor (α7nAChR), involved in the modulation of inflammation and insulin sensitivity, is downregulated in white adipose tissue (WAT) of obese patients. This study aims to test the ability of a selective synthetic α7nAChR agonist, the spirocyclic Δ²-isoxazoline derivative (R)-(-)-ICH3 (ICH3), to counteract acute inflammation and obesity-associated modifications in WAT.

METHODS

We employed the LPS-septic shock murine model, human primary adipocytes and diet-induced obese (DIO) mice. Inflammatory factor expression was assessed by ELISA and quantitative real-time PCR. Flow cytometry was employed to define WAT inflammatory infiltrate. Insulin signaling was monitored by quantification of AKT phosphorylation.

RESULTS

In the septic shock model, ICH3 revealed antipyretic action and reduced the surge of circulating cytokines. In vitro, ICH3 stimulation (10 µM) preserved viability of human adipocytes, decreased IL-6 mRNA (P < 0.05) and blunted LPS-induced peak of TNFα (P < 0.05) and IL-6 (P < 0.01). Chronic administration of ICH3 to DIO mice was associated with lower numbers of CD8+ T cells (P < 0.05) and to changed WAT expression of inflammatory factors (Hp, P < 0.05; CD301/MGL1, P < 0.01; Arg-1, P < 0.05). As compared to untreated, ICH3 DIO mice exhibited improved insulin signaling in the skeletal muscle (P < 0.01) mirrored by an improved response to glucose load (ipGTT: P < 0.05 at 120 min).

CONCLUSIONS

We proved that ICH3 is an anti-inflammatory drug, able to reduce inflammatory cytokines in human adipocytes and to blunt the effects of obesity on WAT inflammatory profile, on glucose tolerance and on tissue insulin sensitivity.

New Rigid Nicotine Analogues, Carrying a Norbornane Moiety, Are Potent Agonists of α7 and α3* Nicotinic Receptors

A three-dimensional database search has been applied to design a series of endo- and exo-3-(pyridin-3-yl)bicyclo[2.2.1]heptan-2-amines as nicotinic receptor ligands. The synthesized compounds were tested in radioligand binding assay on rat cortex against [³H]-cytisine and [³H]-methyllycaconitine to measure their affinity for α4β2* and α7* nicotinic receptors. The new derivatives showed some preference for the α4β2* over the α7* subtype, with their affinity being dependent on the endo/exo isomerism and on the methylation degree of the basic nitrogen. The endo primary amines displayed the lowest K_i values on both receptor subtypes. Selected compounds (1a, 2a, 3a, and 6a) were tested on heterologously expressed α4β2, α7, and α3β2 receptors and on SHSY-5Y cells. Compounds 1a and 2a showed α4β2 antagonistic properties while behaved as full agonists on recombinant α7 and on SHSY5Y cells. On the α3β2 subtype, only the chloro derivative 2a showed full agonist activity and submicromolar potency (EC₅₀ = 0.43 μM). The primary amines described here represent new chemotypes for the α7 and α3* receptor subtypes.

A Small Library of 1,2,3-Triazole Analogs of CAP-55: Synthesis and Binding Affinity at Nicotinic Acetylcholine Receptors

Alpha7 nicotinic acetylcholine receptor is emerging as a central regulator in inflammatory processes, as documented by increasing studies reported in the literature. For instance, the activation of this nicotinic receptor subtype in resident macrophages inhibits the production of pro-inflammatory cytokines, thereby attenuating local inflammatory responses, and may open a new window in the treatment of chronic inflammatory disease, such as Crohn's disease, rheumatoid arthritis, psoriasis, and asthma. In continuation of our ongoing research for the development of new cholinergic drug candidates, we selected the nicotine derivative CAP55, which was previously shown to exert anti-inflammatory effects via nicotinic stimulation, as a suitable compound for lead optimization. Through the isosteric replacement of its 3,5-disubstituted 4,5-dihydroisoxazole core with a 1,4-disubstituted 1,2,3-triazole ring, we could rapidly generate a small library of CAP55-related analogs via a one-pot copper(I)-catalyzed azide-alkyne cycloaddition. Receptor binding assays at nAChRs led to the identification of two promising derivatives, compounds 4 and 10, worthy of further pharmacological studies.

Involvement of Nicotinic Receptor Subtypes in the Behavioral Effects of Nicotinic Drugs in Squirrel Monkeys

Evidence suggests that the α4β2, but not the α7, subtype of the nicotinic acetylcholine receptor (nAChR) plays a key role in mediating the behavioral effects of nicotine and related drugs. However, the importance of other nAChR subtypes remains unclear. The present studies were conducted to examine the involvement of nAChR subtypes by determining the effects of selected nicotinic agonists and antagonists in squirrel monkeys either 1) responding for food reinforcement or 2) discriminating the nicotinic agonist (+)-epibatidine (0.001 mg/kg) from vehicle. In food-reinforcement studies, nicotine, (+)-epibatidine, varenicline and cytisine all produced dose-dependent decreases in rates of food-maintained responding. The rate-decreasing effects of nicotine were antagonized by mecamylamine (nonselective), not appreciably altered by dihydro-β-erythroidine (α4β2 selective), and exacerbated by the nicotinic partial agonists, varenicline and cytisine. Results from discrimination studies show that non-nicotinic drugs did not substitute for (+)-epibatidine, and that except for lobeline, the nicotinic agonists produced either full [(+)-epibatidine, (-)-epibatidine, and nicotine] or partial (varenicline, cytisine, anabaseine, and isoarecolone) substitution for (+)-epibatidine. In interaction studies with antagonists differing in selectivity, (+)-epibatidine discrimination was substantively antagonized by mecamylamine, slightly attenuated by hexamethonium (peripherally restricted) or dihydro-β-erythroidine, and not altered by methyllycaconitine (α7 selective). Varenicline and cytisine enhanced (+)-epibatidine's discriminative-stimulus effects. Correlational analysis revealed a close correspondence between relative behavioral potencies of nicotinic agonists in both studies and their published relative binding affinities at α4β2 and α3β4, but not α7 nAChR, subtypes. Collectively, these results are consistent with the idea that the α4β2 and α3β4, but not α7 nAChR subtypes play a role in the behavioral effects of nicotinic agonists.

Quantitative structure-activity relationship (QSAR) directed the discovery of 3-(pyridin-2-yl)benzenesulfonamide derivatives as novel herbicidal agents

BACKGROUND

Agrochemicals have been crucial to the production of food, and the need for the development of novel agrochemicals continues unceasing owing to the loss of existing produces via the growth of resistance and the desire for products with more propitious environmental and toxicological patterns.

RESULTS

The results of both CoMFA and CoMSIA models indicated that biological activity can effectively be improved through the structural optimisation and molecular design of these synthetic compounds from the aspects of steric, electrostatic, hydrophobic, hydrogen bond donor and acceptor fields. Data of postemergence herbicidal activity in the greenhouse explained that most new 3-(pyridin-2-yl)benzenesulfonamide derivatives (4c-4 t) could control highly effectively against barnyardgrass, foxtail, vetleaf, and youth and old age (herbicidal activity ≥90%); for example, compounds 4q-4 t exhibit excellent biological activity equivalent/superior to commercial saflufenacil/sulcotrione at the low concentration of 37.5 g a.i./ha, and in particular, the herbicidal activity of compound 4 t for four experimental plant species is found to be notably greater than saflufenacil (3.75 g a.i./ha). Meanwhile, compound 4 t also has good crop selectivity for weed control in maize.

CONCLUSION

The novel compounds such as 4 t have remarkable biological activity after the structural optimisation utilising the constructed 3D-QSAR models, i.e. such QSAR models have great accuracy. © 2017 Society of Chemical Industry.

Identification of α7 Nicotinic Acetylcholine Receptor Silent Agonists Based on the Spirocyclic Quinuclidine-Δ2 -Isoxazoline Scaffold: Synthesis and Electrophysiological Evaluation

Compound 11 (3-(benzyloxy)-1'-methyl-1'-azonia-4H-1'-azaspiro[isoxazole-5,3'-bicyclo[2.2.2]octane] iodide) was selected from a previous set of nicotinic ligands as a suitable model compound for the design of new silent agonists of α7 nicotinic acetylcholine receptors (nAChRs). Silent agonists evoke little or no channel activation but can induce the α7 desensitized D_s state, which is sensitive to a type II positive allosteric modulator, such as PNU-120596. Introduction of meta substituents into the benzyloxy moiety of 11 led to two sets of tertiary amines and quaternary ammonium salts based on the spirocyclic quinuclidinyl-Δ² -isoxazoline scaffold. Electrophysiological assays performed on Xenopus laevis oocytes expressing human α7 nAChRs highlighted four compounds that are endowed with a significant silent-agonism profile. Structure-activity relationships of this group of analogues provided evidence of the crucial role of the positive charge at the quaternary quinuclidine nitrogen atom. Moreover, the present study indicates that meta substituents, in particular halogens, on the benzyloxy substructure direct specific interactions that stabilize a desensitized conformational state of the receptor and induce silent activity.

Radiosynthesis of (S)-[18F]T1: The first PET radioligand for molecular imaging of α3β4 nicotinic acetylcholine receptors

Recent pharmacologic data revealed the implication of α3β4 nicotinic acetylcholine receptors (nAChRs) in nicotine and drug addiction. To image α3β4 nAChRs in vivo, we aimed to establish the synthesis of a [¹⁸F]-labelled analog of the highly affine and selective α3β4 ligand (S)-3-(4-(4-fluorophenyl)-1H-1,2,3-triazol-1-yl)quinuclidine ((S)-T1). (S)-[¹⁸F]T1 was synthesized from ethynyl-4-[¹⁸F]fluorobenzene ([¹⁸F]5) and (S)-azidoquinuclidine by click reaction. After a synthesis time of 130min (S)-[¹⁸F]T1 was obtained with a radiochemical yield (non-decay corrected) of 4.3±1.3%, a radiochemical purity of >99% and a molar activity of >158 GBq/μmol. The brain uptake and the brain-to-blood ratio of (S)-[¹⁸F]T1 in mice at 30min post injection were 2.02 (SUV) and 6.1, respectively. According to an ex-vivo analysis, the tracer remained intact (>99%) in brain. Only one major radiometabolite was detected in plasma and urine samples. In-vitro autoradiography on pig brain slices revealed binding of (S)-[¹⁸F]T1 to brain regions associated with the expression of α3β4 nAChRs, which could be reduced by the α3β4 nAChR selective drug AT-1001. These findings make (S)-[¹⁸F]T1 a potential tool for the non-invasive imaging of α3β4 nAChRs in the brain by PET.

Synthesis of chiral cyclic amines via Ir-catalyzed enantioselective hydrogenation of cyclic imines

A highly enantioselective hydrogenation of cyclic imines has been successfully realized providing chiral cyclic amines with excellent enantioselectivities in the absence of any additive.

Sky-blue phosphorescence from bis- and tris-cyclometalated iridium(iii) complexes bearing carbazole-based dendrons: fabrication of non-doped multilayer organic light-emitting diodes by solution processing

Non-doped multilayer OLEDs employing liposoluble and alcohol-insoluble dendrimers were fabricated by solution processing, exhibiting excellent charge balance factors of 0.9.

Varying Chirality Across Nicotinic Acetylcholine Receptor Subtypes: Selective Binding of Quinuclidine Triazole Compounds

The novel quinuclidine anti-1,2,3-triazole derivatives T1-T6 were designed based on the structure of QND8. The binding studies revealed that the stereochemistry at the C3 position of the quinuclidine scaffold plays an important role in the nAChR subtype selectivity. Whereas the (R)-enantiomers are selective to α7 over α4β2 (by factors of 44-225) and to a smaller degree over α3β4 (3-33), their (S)-counterparts prefer α3β4 over α4β2 (62-237) as well as over α7 (5-294). The (R)-derivatives were highly selective to α7 over α3β4 subtypes compared to (RS)- and (R)-QND8. The (S)-enantiomers are 5-10 times more selective to α4β2 than their (R) forms. The overall strongest affinity is observed for the (S)-enantiomer binding to α3β4 (K_i, 2.25-19.5 nM) followed by their (R)-counterpart binding to α7 (K_i, 22.5-117 nM), with a significantly weaker (S)-enantiomer binding to α4β2 (K_i, 414-1980 nM) still above the very weak respective (R)-analogue affinity (K_i, 5059-10436 nM).