Rigidified 2-aminopyrimidines as histamine H4 receptor antagonists: effects of substitution about the rigidifying ring.

Three novel series of histamine H(4) receptor (H(4)R) antagonists containing the 2-aminopyrimidine motif are reported. The best of these compounds display good in vitro potency in both functional and binding assays. In addition, representative compounds are able to completely block itch responses when dosed ip in a mouse model of H(4)-agonist induced scratching, thus demonstrating their activities as H(4)R antagonists.

Subtype-selective Na(v)1.8 sodium channel blockers: identification of potent, orally active nicotinamide derivatives.

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.

Discovery and biological evaluation of potent, selective, orally bioavailable, pyrazine-based blockers of the Na(v)1.8 sodium channel with efficacy in a model of neuropathic pain.

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.

Discovery and biological evaluation of 5-aryl-2-furfuramides, potent and selective blockers of the Nav1.8 sodium channel with efficacy in models of neuropathic and inflammatory pain.

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 (IC50 < 10 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 displayed >100-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.

Discovery of potent furan piperazine sodium channel blockers for treatment of neuropathic 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.

In vitro structure-activity relationship and in vivo characterization of 1-(aryl)-3-(4-(amino)benzyl)urea transient receptor potential vanilloid 1 antagonists.

The synthesis and structure-activity relationship of 1-(aryl)-3-(4-(amino)benzyl)urea transient receptor potential vanilloid 1 (TRPV1) antagonists are described. A variety of cyclic amine substituents are well tolerated at the 4-position of the benzyl group on compounds containing either an isoquinoline or indazole heterocyclic core. These compounds are potent antagonists of capsaicin activation of the TRPV1 receptor in vitro. Analogues, such as compound 45, have been identified that have good in vivo activity in animal models of pain. Further optimization of 45 resulted in compound 58 with substantially improved microsome stability and oral bioavailability, as well as in vivo activity.

Novel transient receptor potential vanilloid 1 receptor antagonists for the treatment of pain: structure-activity relationships for ureas with quinoline, isoquinoline, quinazoline, phthalazine, quinoxaline, and cinnoline moieties.

Novel transient receptor potential vanilloid 1 (TRPV1) receptor antagonists with various bicyclic heteroaromatic pharmacophores were synthesized, and their in vitro activity in blocking capsaicin activation of TRPV1 was assessed. On the basis of the contribution of these pharmacophores to the in vitro potency, they were ranked in the order of 5-isoquinoline > 8-quinoline = 8-quinazoline > 8-isoquinoline > or = cinnoline approximately phthalazine approximately quinoxaline approximately 5-quinoline. The 5-isoquinoline-containing compound 14a (hTRPV1 IC50 = 4 nM) exhibited 46% oral bioavailability and in vivo activity in animal models of visceral and inflammatory pain. Pharmacokinetic and pharmacological properties of 14a are substantial improvements over the profile of the high-throughput screening hit 1 (hTRPV1 IC50 = 22 nM), which was not efficacious in animal pain models and was not orally bioavailable.

Synthesis and structure-activity relationships of a novel series of tricyclic dihydropyridine-based KATP openers that potently inhibit bladder contractions in vitro.

Structure-activity relationships were investigated on a novel series of tricyclic dihydropyridine-containing K(ATP) openers. This diverse group of analogues, comprising a variety of heterocyclic rings fused to the dihydropyridine nucleus, was designed to determine the influence on activity of hydrogen-bond-donating and -accepting groups and their stereochemical disposition. Compounds were evaluated for K(ATP) activity in guinea pig bladder cells using a fluorescence-based membrane potential assay and in a pig bladder strip assay. The inhibition of spontaneous bladder contractions in vitro was also examined for a subset of compounds. All compounds studied showed greater potency to inhibit spontaneous bladder contractions relative to their potencies to inhibit contractions elicited by electrical stimulation.

Synthesis and structure-activity relationships of a novel series of 2,3,5,6,7,9-hexahydrothieno[3,2-b]quinolin-8(4H)-one 1,1-dioxide K(ATP) channel openers: discovery of (-)-(9S)-9-(3-bromo-4-fluorophenyl)-2,3,5,6,7,9- hexahydrothieno[3,2-b]quinolin-8(4H)-one 1,1-dioxide (A-278637), a potent K(ATP) opener that selectively inhibits spontaneous bladder contractions.

Structure-activity relationships were investigated on a novel series of sulfonyldihydropyridine-containing K(ATP) openers. Ring sizes, absolute stereochemistry, and aromatic substitution were evaluated for K(ATP) activity in guinea pig bladder cells using a fluorescence-based membrane potential assay and in a pig bladder strip assay. The inhibition of spontaneous bladder contractions in vitro was also examined for a select group of compounds. All compounds studied showed greater potency to inhibit spontaneous bladder contractions relative to their potencies to inhibit contractions elicited by electrical stimulation. In an anesthetized pig model of myogenic bladder overactivity, compound 14 and (-)-cromakalim 1 were found to inhibit spontaneous bladder contractions in vivo at plasma concentrations lower than those that affected hemodynamic parameters. Compound 14 showed approximately 5-fold greater selectivity than 1 in vivo and supports the concept that bladder-selective K(ATP) channel openers may have utility in the treatment of overactive bladder.

Rotationally constrained 2,4-diamino-5,6-disubstituted pyrimidines: a new class of histamine H4 receptor antagonists with improved druglikeness and in vivo efficacy in pain and inflammation models.

A new structural class of histamine H 4 receptor antagonists (6-14) was designed based on rotationally restricted 2,4-diaminopyrimidines. Series compounds showed potent and selective in vitro H 4 antagonism across multiple species, good CNS penetration, improved PK properties compared to reference H 4 antagonists, functional H 4 antagonism in cellular and in vivo pharmacological assays, and in vivo anti-inflammatory and antinociceptive efficacy. One compound, 10 (A-943931), combined the best features of the series in a single molecule and is an excellent tool compound to probe H 4 pharmacology. It is a potent H 4 antagonist in functional assays across species (FLIPR Ca (2+) flux, K b < 5.7 nM), has high (>190x) selectivity for H 4, and combines good PK in rats and mice (t 1/2 of 2.6 and 1.6 h, oral bioavailability of 37% and 90%) with anti-inflammatory activity (ED 50 = 37 micromol/kg, mouse) and efficacy in pain models (thermal hyperalgesia, ED 50 = 72 micromol/kg, rat).

Alpha-methylation at benzylic fragment of N-aryl-N'-benzyl ureas provides TRPV1 antagonists with better pharmacokinetic properties and higher efficacy in inflammatory pain model.

SAR studies for N-aryl-N'-benzyl urea class of TRPV1 antagonists have been extended to cover alpha-benzyl alkylation. Alkylated compounds showed weaker in vitro potencies in blocking capsaicin activation of TRPV1 receptor, but possessed improved pharmacokinetic properties. Further structural manipulations that included replacement of isoquinoline core with indazole and isolation of single enantiomer led to TRPV1 antagonists like (R)-16a with superior pharmacokinetic properties and greater potency in animal model of inflammatory pain.

A-803467, a potent and selective Nav1.8 sodium channel blocker, attenuates neuropathic and inflammatory pain in the rat.

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 >or=1 microM). 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) approximately 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.

Structure-activity studies of a novel series of 5,6-fused heteroaromatic ureas as TRPV1 antagonists.

Novel 5,6-fused heteroaromatic ureas were synthesized and evaluated for their activity as TRPV1 antagonists. It was found that 4-aminoindoles and indazoles are the preferential cores for the attachment of ureas. Bulky electron-withdrawing groups in the para-position of the aromatic ring of the urea substituents imparted the best in vitro potency at TRPV1. The most potent derivatives were assessed in in vivo inflammatory and neuropathic pain models. Compound 46, containing the indazole core and a 3,4-dichlorophenyl group appended to it via a urea linker, demonstrated in vivo analgesic activity upon oral administration. This derivative also showed selectivity versus other receptors in the CEREP screen and exhibited acceptable cardiovascular safety at levels exceeding the therapeutic dose.

Structure-activity studies for a novel series of tricyclic dihydropyridopyrazolones and dihydropyridoisoxazolones as K(ATP) channel openers.

In search of a novel chemotype of K(ATP) channel openers a series of tricyclic dihydropyridopyrazolones and dihydropyridoisoxazolones was synthesized. It was found that cyclopentanone in the left hand portion of the molecule was 4-fold more potent than cyclohexanone. Introduction of gem-dimethyl groups as well as incorporation of oxygen in the cyclohexanone ring in the left hand portion of the molecule increased the potency 10-fold. In the right hand portion of the molecule, the NH-group of the pyrazolone can be effectively substituted by oxygen increasing the activity 5-fold. Incorporation of a methyl group adjacent to the dihydropyridine (DHP) nitrogen not only significantly boosted activity, but also provided an additional benefit of increased metabolic stability. In vitro tests on the tissue from pig bladder strips provided further confirmation of K(ATP) activity of these compounds.

Structure-Activity studies for a novel series of tricyclic dihydropyrimidines as K(ATP) channel openers (KCOs).

A novel series of tricyclic dihydropyrimidines was synthesized and evaluated for activity as K(ATP) channel openers. The functional activity of several compounds, for example 6A (EC(50)=30nM) and its enantiomers exceeded cromakalim.