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The voltage-gated sodium channel Na

[Image: see text] Cystic fibrosis (CF) is a genetic disorder that affects multiple tissues and organs. CF is caused by mutations in the CFTR gene, resulting in insufficient or impaired cystic fibrosis transmembrane conductance regulator (CFTR) protein. The deletion of phenylalanine at position 508 of the protein (F508del-CFTR) is the most common mutation observed in CF patients. The most effective treatments of these patients employ two CFTR modulator classes, correctors and potentiators. CFTR correctors increase protein levels at the cell surface; CFTR potentiators enable the functional opening of CFTR channels at the cell surface. Triple-combination therapies utilize two distinct corrector molecules (C1 and C2) to further improve the overall efficacy. We identified the need to develop a C2 corrector series that had the potential to be used in conjunction with our existing C1 corrector series and provide robust clinical efficacy for CF patients. The identification of a pyrrolidine series of CFTR C2 correctors and the structure–activity relationship of this series is described. This work resulted in the discovery and selection of (2S,3R,4S,5S)-3-(tert-butyl)-4-((2-methoxy-5-(trifluoromethyl)pyridin-3-yl)methoxy)-1-((S)-tetrahydro-2H-pyran-2-carbonyl)-5-(o-tolyl)pyrrolidine-2-carboxylic acid (ABBV/GLPG-3221), which was advanced to clinical trials.

Cystic fibrosis (CF) is an autosomal recessive disease resulting from mutations on both copies of the CFTR gene. Phenylalanine deletion at position 508 of the CFTR protein (F508del-CFTR) is the most frequent mutation in CF patients. Currently, the most effective treatments of CF use a dual or triple combination of CFTR correctors and potentiators. In triple therapy, two correctors (C1 and C2) and a potentiator are employed. Herein, we describe the identification and exploration of the SAR of a series of 4-aminopyrrolidine-2-carboxylic acid C2 correctors of CFTR to be used in conjunction with our existing C1 corrector series for the treatment of CF.

Na(v)1.8 (also known as PN3) is a tetrodotoxin-resistant (TTx-r) voltage-gated sodium channel (VGSC) that is highly expressed on small diameter sensory neurons. It has been implicated in the pathophysiology of inflammatory and neuropathic pain, and we envisioned that selective blockade of Na(v)1.8 would be analgesic, while reducing adverse events typically associated with non-selective VGSC blocking therapeutic agents. Herein, we describe the preparation and characterization of a series of 6-aryl-2-pyrazinecarboxamides, which are potent blockers of the human Na(v)1.8 channel and also block TTx-r sodium currents in rat dorsal root ganglia (DRG) neurons. Selected derivatives display selectivity versus human Na(v)1.2. We further demonstrate that an example from this series is orally bioavailable and produces antinociceptive activity in vivo in a rodent model of neuropathic pain following oral administration.

A series of aryl-substituted nicotinamide derivatives with selective inhibitory activity against the Na(v)1.8 sodium channel is reported. Replacement of the furan nucleus and homologation of the anilide linker in subtype-selective blocker A-803467 (1) provided potent, selective derivatives with improved aqueous solubility and oral bioavailability. Representative compounds from this series displayed efficacy in rat models of inflammatory and neuropathic pain.

A series of 5-(pyridine-3-yl)octahydropyrrolo[3,4-c]pyrroles have been prepared that exhibit high affinity to alpha4beta2 and/or alpha7 nicotinic acetylcholine receptors (nAChRs). Simple substitution patterns have been identified that allow construction of ligands that are highly selective for either nAChR subtype. The effects of substitution on subtype selectivity provide some insight into the differences in the ligand binding domains of the alpha4beta2 and alpha7 receptors, especially in regions removed from the cation binding pocket.

The voltage-gated sodium channels are a family of proteins that control the flow of sodium ions across cell membranes. Considerable data support the hypothesis that hyperexcitability and spontaneous action potential firing in peripheral sensory neurons mediated by voltage-gated sodium channels contribute to the pathophysiology of chronic pain. Sodium channel blockers are, therefore, appealing entities for therapeutic intervention in painful human neuropathies. This review will focus on the latest advances in the development of small molecule sodium channel blockers and their application to the treatment of chronic pain.

The synthesis and pharmacological characterization of a novel furan-based class of voltage-gated sodium channel blockers is reported. Compounds were evaluated for their ability to block the tetrodotoxin-resistant sodium channel Na(v)1.8 (PN3) as well as the Na(v)1.2 and Na(v)1.5 subtypes. Benchmark compounds from this series possessed enhanced potency, oral bioavailability, and robust efficacy in a rodent model of neuropathic pain, together with improved CNS and cardiovascular safety profiles compared to the clinically used sodium channel blockers mexiletine and lamotrigine.

Nav1.8 (also known as PN3) is a tetrodotoxin-resistant (TTx-r) voltage-gated sodium channel (VGSC) that is highly expressed on small diameter sensory neurons and has been implicated in the pathophysiology of inflammatory and neuropathic pain. Recent studies using an Nav1.8 antisense oligonucleotide in an animal model of chronic pain indicated that selective blockade of Nav1.8 was analgesic and could provide effective analgesia with a reduction in the adverse events associated with nonselective VGSC blocking therapeutic agents. Herein, we describe the preparation and characterization of a series of 5-substituted 2-furfuramides, which are potent, voltage-dependent blockers (IC5010 nM) of the human Nav1.8 channel. Selected derivatives, such as 7 and 27, also blocked TTx-r sodium currents in rat dorsal root ganglia (DRG) neurons with comparable potency and displayed100-fold selectivity versus human sodium (Nav1.2, Nav1.5, Nav1.7) and human ether-a-go-go (hERG) channels. Following systemic administration, compounds 7 and 27 dose-dependently reduced neuropathic and inflammatory pain in experimental rodent models.

Studies in our laboratory are directed at the advancement of synthesis, biology, and medicine. This lecture will focus on new transition metal-catalyzed reactions that have been inspired by biologically potent targets such as phorbol and Taxol® and by the more general interest in producing syntheses that are concise, efficient, cost- and resource-effective, environmentally benign, quick, and simple to conductin essence, ideal. A special emphasis in our program is placed on new transition metal-catalyzed reactions that, in the absence of catalyst, would be forbidden or difficult to achieve. We have thus far reported the first examples of intramolecular metal-catalyzed [4+2], [5+2], and [4+4] cycloadditions, reactions that produce 6-, 7-, and 8-membered rings, respectively. Recent advances in our [5+2] cycloaddition studies will be presented, including new catalysts for relative and absolute stereochemical control. We will also describe recyclable catalysts that can be used in water, thereby minimizing cost and environmental concerns about solvent waste streams. New multicomponent reactions will also be presented. Finally, we will report a new [6+2] cycloaddition that produces an 8-membered ring.

A series of diazabicyclo[3.3.0]octane substituted pyridines and pyrazines was synthesized and characterized at the α4β2 neuronal nicotinic acetylcholine receptor (nAChR). The compounds were designed to mimic the profile of ABT-089, high affinity binding ligand for the α4β2 nAChR, with limited agonist activity. Carboxamide derivatives of 3-(diazabicyclo[3.3.0]octane)-substituted pyridines or 2-(diazabicyclo[3.3.0]octane)-substituted pyrazines were found to have the desired binding and activity profile. The structure-activity relationship of these compounds is presented.

KCNQ2/3 voltage-gated potassium channels conduct low-threshold, slowly activating and non-inactivating currents to repolarize the neuronal resting membrane potential. The channels negatively regulate neuronal excitability and KCNQ2/3 openers are efficacious in hyperexcited states such as epilepsy and pain. We developed and utilized thallium influx assays to profile novel KCNQ2/3 channel openers with respect to selectivity across KCNQ subtypes and on requirement for tryptophan 236 of KCNQ2, a critical residue for activity of the KCNQ opener retigabine. Using distinct chemical series of openers, a quinazolinone series showed relatively poor selectivity across multiple KCNQ channels and lacked activity at the KCNQ2(W236L) mutant channel. In contrast, several novel benzimidazole openers showed selectivity for KCNQ2/3 and KCNQ2 and retain activity at KCNQ2(W236L). Profiling of several hundred KCNQ2/3 openers across multiple diverse chemical series revealed that openers show differential degrees of selectivity across subtypes, with selectivity most difficult to achieve against KCNQ2. In addition, we report the significant finding that KCNQ openers can pharmacologically differentiate between homomeric and heteromeric channels containing subtypes in common. Moreover, most openers assayed were dependent on the W236 for activity, whereas only a small number appear to use a distinct mechanism. Collectively, we provide novel insights into the molecular pharmacology of KCNQ channels by demonstrating differential selectivity and site of action for KCNQ2/3 openers. The high-throughput thallium influx assays should prove useful for rapid characterization of KCNQ openers and in guiding efforts to identify selective compounds for advancement towards the clinic.

Four new bonds and up to four new stereocenters are formed in the title reactions which allow the conversion of readily available starting materials into complex bicyclo[5.4.0]undecane derivatives. The reactions are performed in a single, simple operation that can be conducted on a preparative scale (100 mmol thus far).

Four new bonds and up to four new stereocenters are formed in the title reactions which allow the conversion of readily available starting materials into complex bicyclo[5.4.0]undecane derivatives. The reactions are performed in a single, simple operation that can be conducted on a preparative scale (100 mmol thus far).

Studies in our laboratory are directed at the advancement of synthesis, biology, and medicine. This lecture will focus on new transition metal-catalyzed reactions that have been inspired by biologically potent targets such as phorbol and Taxol ® and by the more general interest in producing syntheses that are concise, efficient, cost- and resource-effective, envi- ronmentally benign, quick, and simple to conduct—in essence, ideal. A special emphasis in our program is placed on new transition metal-catalyzed reactions that, in the absence of cat- alyst, would be forbidden or difficult to achieve. We have thus far reported the first examples of intramolecular metal-catalyzed (4+2), (5+2), and (4+4) cycloadditions, reactions that pro- duce 6-, 7-, and 8-membered rings, respectively. Recent advances in our (5+2) cycloaddition studies will be presented, including new catalysts for relative and absolute stereochemical control. We will also describe recyclable catalysts that can be used in water, thereby mini- mizing cost and environmental concerns about solvent waste streams. New multicomponent reactions will also be presented. Finally, we will report a new (6+2) cycloaddition that pro- duces an 8-membered ring.

Described herein is an efficient preparative scale synthesis of 1-(2-methyoxyethoxy)-1-vinylcyclopropane and the investigation of the utility of this reagent as a new five-carbon component in metal-catalyzed [5 + 2] cycloadditions. A new cycloaddition procedure is also described that proceeds up to 12-fold faster and with 10-fold less catalyst than previously described, providing cycloheptenones in many cases in minutes and in isolated yields of 75−97%. The procedure is readily conducted on a small or large scale (up to 100 mmol thus far).

Evidence implicating Nav1.8 and TRPV1 ion channels in various chronic pain states is extensive. In this study, we used isobolographic analysis to examine the in vivo effects of the combination of the Nav1.8 blocker A-803467 [5-(4-Chloro-phenyl)-furan-2-carboxylic acid (3,5-dimethoxy-phenyl)-amide] with 2 structurally distinct TRPV1 antagonists, A-840257 [1-(1H-Indazol-4-yl)-3-([R]-4-piperidin-1-yl-indan-1-yl)-urea] or A-425619 [1-Isoquinolin-5-yl-3-(4-trifluoromethyl-benzyl)-urea]. The antinociceptive effects of the Nav1.8 blocker alone and in combination with each TRPV1 antagonist were examined in an inflammatory (complete Freund's adjuvant, CFA) and a neuropathic (spinal nerve ligation, SNL) pain model after systemic (intraperitoneal) administration. Alone, A-803467 was efficacious in both CFA and SNL models with ED 50 values of 70 (54.2 to 95.8) mg/kg and 70 (38.1 to 111.9) mg/kg, respectively. The ED 50 values of the TRPV1 antagonists A-840257 and A-425619 alone in the CFA model were 10 (3.6 to 14.9) mg/kg and 43 (24.1 to 62.2) mg/kg, respectively; both were without significant effect in the SNL model. A series of experiments incorporating 1:1, 3:1, or 0.3:1 ED 50 dose-ratio combinations of A-840257 and A-803467, or A-425619 and A-803467 were performed in both pain models, and the effective doses of mixtures that produced 50% antinociception (ED 50, mix ) were determined by isobolographic analysis. The ED 50, mix in each case was not found to be statistically different than ED 50, add , the theoretical ED 50 calculated assuming additive effects. These data demonstrate that Nav1.8 blockers and TRPV1 antagonists administered in combination produce an additive effect in rat pain models. Using such a combination strategy to produce analgesia may potentially provide an improved therapeutic separation from unwanted in vivo side effects associated with blockade of either Nav1.8 or TRPV1 alone. Perspective In this report, effects of coadministration of TRPV1 antagonists and A-803467, a Nav1.8 blocker, were investigated in preclinical rodent models of neuropathic and inflammatory pain. The 2 classes of novel antinociceptive agents produced an additive interaction in attenuating CFA-induced thermal hyperalgesia, providing a rationale for their use as a combination strategy in the clinic for treating inflammatory pain.

We have recently reported that systemic delivery of A-803467 [5-(4-chlorophenyl-N-(3,5-dimethoxyphenyl)furan-2-carboxamide], a selective Na(v)1.8 sodium channel blocker, reduces behavioral measures of chronic pain. In the current study, the effects of A-803467 on evoked and spontaneous firing of wide dynamic range (WDR) neurons were measured in uninjured and rats with spinal nerve ligations (SNLs). Administration of A-803467 (10-30 mg/kg i.v.) reduced mechanically evoked (10-g von Frey hair) and spontaneous WDR neuronal activity in SNL rats. In uninjured rats, A-803467 (20 mg/kg i.v.) transiently reduced evoked but not spontaneous firing of WDR neurons. The systemic effects of A-803467 in SNL rats were not altered by spinal transection or by systemic pretreatment with the transient receptor potential vanilloid type 1 (TRPV1) receptor agonist, resiniferatoxin, at doses that impair the function of TRPV1-expressing fibers. To determine sites of action, A-803467 was administered into spinal tissue, into the uninjured L4 dorsal root ganglion (DRG), or into the neuronal receptive field. Injections of A-803467 into the L4 DRG (30-100 nmol/1 mul) or into the hindpaw receptive field (300 nmol/50 mul) reduced evoked but not spontaneous WDR firing. In contrast, intraspinal (50-150 nmol/0.5 mul) injection of A-803467 decreased both evoked and spontaneous discharges of WDR neurons. Thus, Na(v)1.8 sodium channels on the cell bodies/axons within the L4 DRG as well as on peripheral and central terminals of primary afferent neurons regulate the inflow of low-intensity mechanical signals to spinal WDR neurons. However, Na(v)1.8 sodium channels on central terminals seem to be key to the modulation of spontaneous firing in SNL rats.

Activation of tetrodotoxin-resistant sodium channels contributes to action potential electrogenesis in neurons. Antisense oligonucleotide studies directed against Na v 1.8 have shown that this channel contributes to experimental inflammatory and neuropathic pain. We report here the discovery of A-803467, a sodium channel blocker that potently blocks tetrodotoxin-resistant currents (IC 50 = 140 nM) and the generation of spontaneous and electrically evoked action potentials in vitro in rat dorsal root ganglion neurons. In recombinant cell lines, A-803467 potently blocked human Na v 1.8 (IC 50 = 8 nM) and was >100-fold selective vs. human Na v 1.2, Na v 1.3, Na v 1.5, and Na v 1.7 (IC 50 values ≥1 μM). A-803467 (20 mg/kg, i.v.) blocked mechanically evoked firing of wide dynamic range neurons in the rat spinal dorsal horn. A-803467 also dose-dependently reduced mechanical allodynia in a variety of rat pain models including: spinal nerve ligation (ED 50 = 47 mg/kg, i.p.), sciatic nerve injury (ED 50 = 85 mg/kg, i.p.), capsaicin-induced secondary mechanical allodynia (ED 50 ≈ 100 mg/kg, i.p.), and thermal hyperalgesia after intraplantar complete Freund's adjuvant injection (ED 50 = 41 mg/kg, i.p.). A-803467 was inactive against formalin-induced nociception and acute thermal and postoperative pain. These data demonstrate that acute and selective pharmacological blockade of Na v 1.8 sodium channels in vivo produces significant antinociception in animal models of neuropathic and inflammatory pain.

The first example of a transition metal-catalyzed hetero-[5 + 2] cycloaddition reaction is described. Use of cyclopropyl imines as five-atom components, an alkyne as a two-carbon component, and a Rh(I) catalyst enables a new route to dihydroazepines. This new hetero-[5 + 2] cycloaddition works well with aldimines, ketimines, and with substituted cyclopropanes and affords the desired dihydroazepines in excellent yields as single regioisomers. Use of serial imine formation/aza-[5 + 2] cycloaddition generates the desired dihydroazepines in one operation from three commercially available starting materials. The reaction has been scaled to give gram quantities of dihydroazepine.