Synthesis and activity of 3-pyridylamine ligands at central nicotinic receptors

Discovery and Development of 3-(6-Chloropyridine-3-yloxymethyl)-2-azabicyclo[3.1.0]hexane Hydrochloride (SUVN-911): A Novel, Potent, Selective, and Orally Active Neuronal Nicotinic Acetylcholine α4β2 Receptor Antagonist for the Treatment of Depression

A series of chemical optimizations guided by in vitro affinity at the α4β2 receptor in combination with selectivity against the α3β4 receptor, pharmacokinetic evaluation, and in vivo efficacy in a forced swim test resulted in identification of 3-(6-chloropyridine-3-yloxymethyl)-2-azabicyclo[3.1.0]hexane hydrochloride (9h, SUVN-911) as a clinical candidate. Compound 9h is a potent α4β2 receptor ligand with a K_i value of 1.5 nM. It showed >10 μM binding affinity toward the ganglionic α3β4 receptor apart from showing selectivity over 70 other targets. It is orally bioavailable and showed good brain penetration in rats. Marked antidepressant activity and dose-dependent receptor occupancy in rats support its potential therapeutic utility in the treatment of depression. It does not affect the locomotor activity at doses several folds higher than its efficacy dose. It is devoid of cardiovascular and gastrointestinal side effects. Successful long-term safety studies in animals and phase-1 evaluation in healthy humans for safety, tolerability, and pharmacokinetics paved the way for its further development.

The Oncolytic Efficacy and in Vivo Pharmacokinetics of [2-(4-Chlorophenyl)quinolin-4-yl](piperidine-2-yl)methanol (Vacquinol-1) Are Governed by Distinct Stereochemical Features

Glioblastoma remains an incurable brain cancer. Drugs developed in the past 20 years have not improved the prognosis for patients, necessitating the development of new treatments. We have previously reported the therapeutic potential of the quinoline methanol Vacquinol-1 (1) that targets glioblastoma cells and induces cell death by catastrophic vacuolization. Compound 1 is a mixture of four stereoisomers due to the two adjacent stereogenic centers in the molecule, complicating further development in the preclinical setting. This work describes the isolation and characterization of the individual isomers of 1 and shows that these display stereospecific pharmacokinetic and pharmacodynamic features. In addition, we present a stereoselective synthesis of the active isomers, providing a basis for further development of this compound series into a novel experimental therapeutic for glioblastoma.

The design of 8-hydroxyquinoline tetracyclic lactams as HIV-1 integrase strand transfer inhibitors

A novel series of HIV-1 integrase strand transfer inhibitors were designed using the venerable two-metal binding pharmacophore model and incorporating structural elements from two different literature scaffolds. This manuscript describes a number of 8-hydroxyquinoline tetracyclic lactams with exceptional antiviral activity against HIV-1 and little loss of potency against the IN signature resistance mutations Q148K and G140S/Q148H.

A Facile N-monoalkylation of Aminopyridines

The N-monoalkylation of 2- or 3-aminopyridines by a carboxylic acid and sodium borohydride afforded the corresponding alkylaminopyridine under mild conditions in good yields. N-Alkylaminopyridines are important intermediate for preparing N-containing heterocycles, such as “flytrap” aminopyridinium-based anion hosts and pharmaceuticals.

Synthesis and biological activity of a novel class nicotinic acetylcholine receptors (nAChRs) ligands structurally related to anatoxin-a

The introduction of the isoxazole ring as bioisosteric replacement of the acetyl group of anatoxin-a led to a new series of derivatives binding to nicotinic acetylcholine receptors. Bulkier substitutions than methyl at the 3 position of isoxazole were shown to be detrimental for the activity. The binding potency of the most interesting compounds with α1, α7 and α3β4 receptor subtypes, was, anyway, only at micromolar level. Moreover, differently from known derivatives with pyridine, isoxazole condensed to azabicyclo ring led to no activity.

Hit-to-lead optimization of disubstituted oxadiazoles and tetrazoles as mGluR5 NAMs

Here we report the discovery and early SAR of a series of mGluR5 negative allosteric modulators (NAMs). Starting from a moderately active HTS hit we synthesized 3,5-disubstituted-oxadiazoles and tetrazoles as mGluR5 NAMs. Based on the analysis of ligand efficiency and lipophilic efficiency metrics we identified a promising lead candidate as a starting point for further optimization.

Total synthesis studies on macrocyclic pipecolic acid natural products: FK506, the antascomicins and rapamycin

This chapter derives its inspiration from the challenges presented to total synthesis chemists, by a particular group of macrocyclic pipecolic acid natural products. Although there is considerable emphasis on the completed syntheses of the main characters (FK506 (1), the antascomycins (4 and 5) and rapamycin (7)), the overall complexity of the molecular problem has stimulated a wealth of new knowledge, including the development of novel strategies and the invention of new synthetic methods. The ingenious and innovative approaches to these targets have enabled new generations of analogues, and provided material to further probe the biology of these fascinating molecules. With pharmaceutical application as an immunosuppressant, as well as potential use for the treatment of cancer and neurodegenerative diseases, this family of natural products continues to inspire new and interesting science while providing solutions to healthcare problems of the world.

Intramolecular Conjugate Displacement: A General Route to Hexahydroquinolizines, Hexahydroindolizines, and Related [m,n,0]-Bicyclic Structures with Nitrogen at a Bridgehead

N-Protected amino aldehydes can be converted into allylic alcohols by the classical Morita-Baylis-Hillman reaction (cf. 2 --> 3) or by condensation with selenium-stabilized carbanions, followed by oxidation (cf. 2 --> 8 --> 3). The derived acetates undergo cyclization when the nitrogen protecting group is removed, affording [m,n,0]-bicyclic structures with nitrogen at a bridgehead (cf. 4 --> 5 --> 6). Formation of bicyclic structures via the reactions of Schemes 1 and 2 is general, and the stereochemistry of the starting amino aldehyde is preserved.

N, N -disubstituted piperazines and homopiperazines: synthesis and affinities at alpha4beta2* and alpha7* neuronal nicotinic acetylcholine receptors

A series of N, N- disubstituted piperazines and homopiperazines were prepared and evaluated for binding to natural alpha4beta2* and alpha7* neuronal nicotinic acetylcholine receptors (nAChRs) using whole brain membrane. Some compounds exhibited good selectivity for alpha4beta2* nAChRs and did not interact with the alpha7* nAChRs subtype. The most potent analogs were compounds 8-19 (K(i) = 10.4 microM), 8-13 (K(i) = 12.0 microM), and 8-24 (K(i) = 12.8 microM). Thus, linking together a pyridine pi-system and a cyclic amine moiety via a homopiperazine ring affords compounds with low affinity but with good selectivity for alpha4beta2* nAChRs.

Synthesis and analgesic activity of secondary amine analogues of pyridylmethylamine and positional isomeric analogues of ABT-594

A series of highly sterically hindered secondary amine analogues of pyridylmethylamine (7a-f, 8a-c) and positional isomeric analogues of ABT-594 (9a-c) were synthesized and evaluated for their in vivo analgesic activity. The compounds 7a and 7d show potent analgesic activity and lower toxicity. Some interesting structure-activity relationships have been revealed.

Docking of 6-chloropyridazin-3-yl derivatives active on nicotinic acetylcholine receptors into molluscan acetylcholine binding protein (AChBP)

The crystal structure of Acetylcholine Binding Protein (AChBP), homolog of the ligand binding domain of nAChR, has been used as model for computational investigations on the ligand-receptor interactions of derivatives of 6-chloropyridazine substituted at C3 with 3,8-diazabicyclo[3.2.1]octane, 2,5-diazabicyclo[2.2.1]heptane and with piperazine and homopiperazine, substituted or not at N4. The ligand-receptor complexes have been analyzed by docking techniques using the binding site of HEPES complexed with AChBP as template. The good relationship between the observed binding affinity and the calculated docking energy confirms that this model provides a good starting point for understanding the binding domain of neuronal nicotinic receptors. An analysis of the possible factors significant for the ligand recognition has evidenced, besides the cation-pi interaction, the distance between the chlorine atom of the pyridazinyl group and the carbonylic oxygen of Leu B112 as an important parameter in the modulation of the binding energy.

Nicotinic agonists, antagonists, and modulators from natural sources

1. Acetylcholine receptors were initially defined as nicotinic or muscarinic, based on selective activation by two natural products, nicotine and muscarine. Several further nicotinic agonists have been discovered from natural sources, including cytisine, anatoxin, ferruginine, anabaseine, epibatidine, and epiquinamide. These have provided lead structures for the design of a wide range of synthetic agents. 2. Natural sources have also provided competitive nicotinic antagonists, such as the Erythrina alkaloids, the tubocurarines, and methyllycaconitine. Noncompetitive antagonists, such as the histrionicotoxins, various izidines, decahydroquinolines, spiropyrrolizidine oximes, pseudophrynamines, ibogaine, strychnine, cocaine, and sparteine have come from natural sources. Finally, galanthamine, codeine, and ivermectin represent positive modulators of nicotinic function, derived from natural sources. 3. Clearly, research on acetylcholine receptors and functions has been dependent on key natural products and the synthetic agents that they inspired.

Selective Amination of Polyhalopyridines Catalyzed by a Palladium−Xantphos Complex

[reaction: see text] Amination of 5-bromo-2-chloropyridine (1a) catalyzed by a palladium-Xantphos complex predominately gives 5-amino-2-chloropyridine product 3a in 96% isolated yield and excellent chemoselectivity (3a/4a = 97:3). Amination of 2,5-dibromopyridine (11) under the same conditions exclusively affords 2-amino-5-bromopyridine 4a.

Cholinergic nicotinic receptors: competitive ligands, allosteric modulators, and their potential applications

Discovery of the important role played by nicotinic acetylcholine receptors (nAChRs) in several CNS disorders has called attention to these membrane proteins and to ligands able to modulate their functions. The existence of different subtypes at multiple levels has complicated the understanding of this receptor's physiological role, but at the same time has increased the efforts to discover selective compounds in order to improve the pharmacological characterization of this kind of receptor and to make the possible therapeutical use of its modulators safer. This review focuses on the structure of new ligands for nAChRs, agonists, antagonists and allosteric modulators, and on their possible applications.

N,N-disubstituted piperazines: synthesis and affinities at alpha4beta2(*) and alpha7(*) neuronal nicotinic acetylcholine receptors

A series of N,N-disubstituted piperazines were prepared and evaluated for binding to alpha4beta2(*) and alpha7(*) neuronal nicotinic acetylcholine receptors using rat striatum and whole brain membrane preparations, respectively. This series of compounds exhibited selectivity for alpha4beta2(*) nAChRs and did not interact with the alpha7(*) nAChRs subtype. The most potent analogues were compounds 8b and 8f (K(i)=32 microM). Thus, linking together a pyridine pi-system and a cyclic amine moiety via a piperazine ring affords compounds with low affinity, but good selectivity for alpha4beta2(*) nicotinic receptors.

A comparison of the binding of three series of nicotinic ligands

A total of 24 aryl-substituted analogues of nicotine (1a) and two related series of nicotinic ligands, aminomethylpyridines 3 and ether analogues 8, were examined to determine if they bind at alpha4beta2 nACh receptors in a common manner. A modest correlation (r=0.785) was found between the affinities of the nicotine analogues and derivatives of 3, but little correlation (r=0.348) was found with analogues 8. However, a modest correlation (r=0.742) exists between the binding of analogues 3 and 8. It seems that 1-series and 8-series compounds bind differently but that the 3-series compounds share some intermediate binding similarity with both.