Design, synthesis, and pharmacological evaluation of JDTic analogs to examine the significance of replacement of the 3-hydroxyphenyl group with pyridine or thiophene bioisosteres.

The potent and selective KOR antagonist JDTic was derived from the N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine class of pure opioid antagonists. In previous studies we reported that compounds that did not have a hydroxyl on the 3-hydroxyphenyl group and did not have methyl groups at the 3- and 4-position of the piperidine ring were still potent and selective KOR antagonists. In this study we report JDTic analogs 2, 3a-b, 4a-b, and 5, where the 3-hydroxyphenyl ring has been replaced by a 2-, 3-, or 4-pyridyl or 3-thienyl group and do not have the 3-methyl or 3,4-dimethyl groups, remain potent and selective KOR antagonists. Of these, (3R)-7-hydroxy-N-(1S)-2-methyl-[4-methyl-4-pyridine-3-yl-carboxamide (3b) had the best overall binding potency and selectivity in a [(35)S]GTPγS functional assay, with a Ke=0.18nM at the KOR and 273- and 16,700-fold selectivity for the KOR relative to the MOR and DOR, respectively. Calculated physiochemical properties for 3b suggest that it will cross the blood-brain barrier.

Discovery of a novel small molecule agonist scaffold for the APJ receptor.

The apelinergic system includes a series of endogenous peptides apelin, ELABELA/TODDLER and their 7-transmembrane G-protein coupled apelin receptor (APJ, AGTRL-1, APLNR). The APJ receptor is an attractive therapeutic target because of its involvement in cardiovascular diseases and potentially other disorders including liver fibrosis, obesity, diabetes, and neuroprotection. To date, pharmacological characterization of the APJ receptor has been limited due to the lack of small molecule functional agonists or antagonists. Through focused screening we identified a drug-like small molecule agonist hit 1 with a functional EC50 value of 21.5±5µM and binding affinity (Ki) of 5.2±0.5µM. Initial structure-activity studies afforded compound 22 having a 27-fold enhancement in potency and the first sub-micromolar full agonist with an EC50 value of 800±0.1nM and Ki of 1.3±0.3µM. Preliminary SAR, synthetic methodology, and in vitro pharmacological characterization indicate this scaffold will serve as a favorable starting point for further refinement of APJ potency and selectivity.

The amide linker in nonpeptide neurotensin receptor ligands plays a key role in calcium signaling at the neurotensin receptor type 2.

Compounds acting via the GPCR neurotensin receptor type 2 (NTS2) display analgesia in relevant preclinical models. The amide bond in nonpeptide NTS1 antagonists plays a central role in receptor recognition and molecular conformation. Using NTS2 FLIPR and binding assays, we found that it is also a key molecular structure for binding and calcium mobilization at NTS2. We found that reversed amides display a shift from agonist to antagonist activity and provided examples of the first competitive nonpeptide antagonists observed in the NTS2 FLIPR assay. These compounds will be valuable tools for determining the role of calcium signaling in vitro to NTS2 mediated analgesia.

Identification of N-{[6-chloro-4-(2,6-dimethoxyphenyl)quinazolin-2-yl]carbonyl}-l-leucine (NTRC-808), a novel nonpeptide chemotype selective for the neurotensin receptor type 2.

Compounds acting via the GPCR neurotensin receptor type 2 (NTS2) display analgesic effects in relevant animal models. Using a pharmacophore model based on known NT receptor nonpeptide compounds, we screened commercial databases to identify compounds that might possess activity at NTS2 receptor sites. Modification of our screening hit to include structural features known to be recognized by NTS1 and NTS2, led to the identification of the novel NTS2 selective nonpeptide, N-{[6-chloro-4-(2,6-dimethoxyphenyl)quinazolin-2-yl]carbonyl}-l-leucine (9). This compound is a potent partial agonist in the FLIPR assay with a profile of activity similar to that of the reference NTS2 analgesic nonpeptide levocabastine (5).

Design, synthesis, and pharmacological evaluation of JDTic analogs to examine the significance of the 3- and 4-methyl substituents.

The design and discovery of JDTic as a potent and selective kappa opioid receptor antagonist used the N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine pharmacophore as the lead structure. In order to determine if the 3-methyl or 4-methyl groups were necessary in JDTic and JDTic analogs for antagonistic activity, compounds 4a-c, and 4d-f which have either the 3-methyl or both the 3- and 4-methyl groups removed, respectively, from JDTic and analogs were synthesized and evaluated for their in vitro opioid receptor antagonist activities using a [(35)S]GTPγS binding assay. Other ADME properties were also assessed for selected compounds. These studies demonstrated that neither the 3-methyl or 3,4-dimethyl groups present in JDTic and analogs are required to produce potent and selective κ opioid receptor antagonists.

Imidazole-derived agonists for the neurotensin 1 receptor.

A scaffold-hop program seeking full agonists of the neurotensin-1 (NTR1) receptor identified the probe molecule ML301 (1) and associated analogs, including its naphthyl analog (14) which exhibited similar properties. Compound 1 showed full agonist behavior (79-93%) with an EC50 of 2.0-4.1µM against NTR1. Compound 1 also showed good activity in a Ca mobilization FLIPR assay (93% efficacy at 298nM), consistent with it functioning via the Gq coupled pathway, and good selectivity relative to NTR2 and GPR35. In further profiling, 1 showed low potential for promiscuity and good overall pharmacological data. This report describes the discovery, synthesis, and SAR of 1 and associated analogs. Initial in vitro pharmacologic characterization is also presented.

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.

The identification of nonpeptide neurotensin receptor partial agonists from the potent antagonist SR48692 using a calcium mobilization assay.

In a search for nonpeptide agonists for the neurotensin receptor (NTR1), we replaced the adamantyl amino acid moiety found in the antagonist SR48692 (1a) with leucine and related alpha-alkylamino acids found in peptide agonists. When tested in a calcium mobilization assay, we found that both d- and l-leucine confer partial agonist activity to the pyrazole scaffold with the l-enantiomer (3a) providing a significantly greater response. A brief SAR survey demonstrated that the observed agonist activity was resilient to changes made to the dimethoxyaryl ring in 3a. The resulting compounds were less potent relative to 3a but showed greater agonist responses. The partial agonist activity was extinguished when the chloroquinoline ring was replaced with naphthalene. Thus, while l-leucine appears to possess a powerful agonist directing affect for the NTR1 receptor, its presence alone in the molecular architecture is not sufficient to insure agonist behavior.

The effect of kappa-opioid receptor agonists on tetrodotoxin-resistant sodium channels in primary sensory neurons.

BACKGROUND: A non-opioid receptor-mediated inhibition of sodium channels in dorsal root ganglia (DRGs) by kappa-opioid receptor agonists (kappa-ORAs) has been reported to contribute to the antinociceptive actions in animals and humans. In this study, we examined structurally diverse kappa-ORAs for their abilities to inhibit tetrodotoxin-resistant (TTX-r) sodium channels in adult rat DRGs. METHODS: Whole-cell recordings of TTX-r sodium currents were performed on cultured adult rat DRGs. Structurally diverse kappa-ORAs were studied for their abilities to inhibit TTX-r sodium channels. RESULTS: The racemic kappa-ORA, (+/-)U50,488, inhibited TTX-r sodium currents in a voltage-dependent manner, yielding IC(50) values of 49 and 8 muM, at prepulse potentials of -100 and -40 mV, respectively. Furthermore, we found that both the kappa-ORA U50,488 active enantiomer 1S,2S U50,488 and the inactive enantiomer 1R,2R U50,488 were equally potent inhibitors of TTX-r sodium currents. Structurally related kappa-ORAs, such as BRL 52537 and ICI 199,441 also inhibited TTX-r sodium currents. However, sodium channel inhibition and kappa-opioid receptor agonism have a distinct structure-activity relationship because another kappa-ORA (ICI 204,488) was inactive versus TTX-r sodium channels. We further investigated the sodium channel block of this class of compounds by studying (+/-)U50,488. (+/-)U50,488 was found to preferentially interact with the slow inactivated state of TTX-r sodium channels and to retard recovery from inactivation. CONCLUSION: Our results suggest that TTX-r sodium channels can be inhibited by many kappa-ORAs via an opioid receptor-independent mechanism. Although the potency for sodium channel inhibition is typically much less than apparent affinity for opioid receptors, sodium channel block may still contribute to the antinociceptive effects of this class of compounds.

Synthesis and in vitro opioid receptor functional antagonism of analogues of the selective kappa opioid receptor antagonist (3R)-7-hydroxy-N-((1S)-1-{[(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinyl]methyl}-2-methylpropyl)-1,2,3,4-tetrahydro-3-isoquinolinecarboxamide (JDTic).

In previous structure-activity relationship (SAR) studies, we identified (3 R)-7-hydroxy- N-((1 S)-1-{[(3 R,4 R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinyl]methyl}-2-methylpropyl)-1,2,3,4-tetrahydro-3-isoquinolinecarboxamide (JDTic, 1) as the first potent and selective kappa opioid receptor antagonist from the trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine class of opioid antagonist. In the present study, we report the synthesis and in vitro opioid receptor functional antagonism of a number of analogues of 1 using a [ (35) S]GTPgammaS binding assay. The results from the studies better define the pharmacophore for this class of kappa opioid receptor antagonist and has identified new potent and selective kappa antagonist. (3 R)-7-Hydroxy- N-[(1 S,2 S)-1-{[(3 R,4 R)-4-(3-hydroxyphenyl)-3,4-dimethylpiperidin-1-yl]methyl}-2-methylbutyl]-1,2,3,4-tetrahydroisoquinoline-3-carboxamide ( 3) with a K e value of 0.03 nM at the kappa receptor and 100- and 793-fold selectivity relative to the mu and delta receptors was the most potent and selective kappa opioid receptor antagonist identified.

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.

A new synthesis of the ORL-1 antagonist 1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidinyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (J-113397) and activity in a calcium mobilization assay.

A new chiral synthesis of the ORL-1 antagonist 1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidinyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (2, J-113397) was developed. J-113397 has a K(e)=0.85nM in an ORL-1 calcium mobilization assay and is 89-, 887-, and 227-fold selective for the ORL-1 receptor relative to the mu, delta, and kappa opioid receptors.

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.

Potent and Selective Tetrahydroisoquinoline Kappa Opioid Receptor Antagonists of Lead Compound (3 R)- N-[1 R)-1-(Cyclohexylmethyl)-2-methylpropyl]-7-hydroxy-1,2,3,4-tetrahydroisoquinoline-3-carboxamide (CDTic).

Animal pharmacological studies suggest that potent and selective κ opioid receptor antagonists have potential as pharmacotherapies targeting depression, anxiety, and substance abuse (opiates, alcohol, nicotine, cocaine). We recently reported lead compound 1 as a new class of κ opioid receptor antagonists with only one basic amine group. Analogues were synthesized and evaluated for their in vitro opioid receptor antagonist properties using a [35S]GTPγS binding assay. All analogues were pure opioid receptor antagonists with no agonist activity. Compounds 1, 8, 9, 13, and 14 ( Ke values 0.058-0.64 nM) are highly potent and highly selective for the κ relative to the µ and δ opioid receptors. Favorable calculated physiochemical properties were confirmed in rat PK studies, demonstrating brain penetration for selected compounds 1, 9, and 13. High κ opioid receptor potency and selectivity and highly favorable calculated physiochemical and PK properties for brain penetration suggest these compounds should be considered for further development.

Potent and Selective Tetrahydroisoquinoline Kappa Opioid Receptor Antagonists of Lead Compound (3 R)-7-Hydroxy- N-[(1 S)-2-methyl-1-(piperidin-1-ylmethyl)propyl]-1,2,3,4-tetrahydroisoquinoline-3-carboxamide (PDTic).

Past studies have shown that it has been difficult to discover and develop potent and selective κ opioid receptor antagonists, particularly compounds having potential for clinical development. In this study, we present a structure-activity relationship (SAR) study of a recently discovered new class of tetrahydroisoquinoline κ opioid receptor antagonists which led to (3 R)-7-hydroxy- N-{(1 S)-2-methyl-1-[(-4-methylpiperidine-1-yl)methyl]propyl}-1,2,3,4-tetrahydroisoquinoline-3-carboxamide (12) (4-Me-PDTic). Compound 12 had a Ke = 0.37 nM in a [35S]GTPγS binding assay and was 645- and >8100-fold selective for the κ relative to the µ and δ opioid receptors, respectively. Calculated log BB and CNS (central nervous system) multiparameter optimization (MPO) and low molecular weight values all predict that 12 will penetrate the brain, and pharmacokinetic studies in rats show that 12 does indeed penetrate the brain.

Anxiolytic-like effects of kappa-opioid receptor antagonists in models of unlearned and learned fear in rats.

Endogenous opioid systems regulate neurobiological responses to threatening stimuli. Stimulation of kappa-opioid receptors (KORs) produces analgesia but induces prodepressive-like effects in a variety of animal models. In contrast, KOR antagonists have antidepressant-like effects. KORs and their endogenous ligand dynorphin are expressed throughout brain areas involved in fear and anxiety, including the extended amygdala. Here, we examined whether KOR antagonists would affect unlearned fear (anxiety) in the elevated plus maze (EPM) and open field (OF) paradigms and learned fear in the fear-potentiated startle (FPS) paradigm. These studies were designed to accommodate the slow onset (approximately 24 h) and extended time course (>3 weeks) of the prototypical KOR antagonists nor-binaltorphimine hydrochloride (norBNI) and JDTic [(3R)-7-hydroxy-N-[(1S)-1-[[(3R, 4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinyl]methyl]-2-methylpropyl]-1,2,3,4-tetrahydro-3-isoquinoline-carboxamide hydrochloride]. Rats received an i.p. injection of norBNI (3.0-30 mg/kg) or JDTic (1.0-10 mg/kg) 48 h before EPM testing. One day later, they were tested in the OF, and 5 and 7 days later, they were trained and tested in the FPS paradigm. Both KOR antagonists dose-dependently increased open arm exploration in the EPM without affecting OF behavior. They also decreased conditioned fear in the FPS paradigm. The anxiolytic-like effects of KOR antagonists were qualitatively similar to those of the benzodiazepine chlordiazepoxide in the EPM. The selective serotonin reuptake inhibitor fluoxetine had no effect in the EPM and anxiogenic-like effects in the OF. Our results indicate that KOR antagonists produce a unique combination of antidepressant- and anxiolytic-like effects and suggest that this class of drugs may be particularly effective for the treatment of comorbid depressive and anxiety disorders.

Simple Tetrahydroisoquinolines Are Potent and Selective Kappa Opioid Receptor Antagonists.

Potent and selective κ opioid receptor antagonists have been derived from the N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine class of pure opioid receptor antagonists. In order to determine if the 3-hydroxyphenyl and/or the piperidine amino groups are required for obtaining the pure opioid antagonists, (3R)-7-hydroxy-N-[(1S)-2-methyl-1-(piperidine-1-ylmethyl)propyl]-1,2,3,4-tetrahydroiosquinoline-3-carboxamide (1), which does not have a 4-(3-hydroxyphenyl) group, and (3R)-N-(1R)-1-(cyclohexylmethyl)-2-methylpropyl]-7-hydroxy-1,2,3,4-tetrahydroisoquinoline-3-carboxamide (2), which does not have a 4-hydroxylphenyl or a piperidine amino group, were synthesized and evaluated for their [35S]GTPγS binding properties at the µ, δ, and κ opioid receptors. Surprisingly compound 1 remained a pure opioid antagonist with a Ke = 6.80 nM at the κ opioid receptor and is 21- and 441-fold selective for the κ receptor relative to the µ and δ opioid receptors, respectively. Even more unexpected and novel is the finding that 2 has a Ke = 0.14 nM at κ and is 1730- and 4570-fold selective for κ relative to the µ and δ opioid receptors, respectively.

Highly potent and selective phenylmorphan-based inverse agonists of the opioid delta receptor.

We recently reported the discovery of (+)-5-(3-hydroxyphenyl)-4-methyl-2-(3-phenylpropyl)-2-azabicyclo[3.3.1]non-7-yl-(1-phenyl-1-cyclopentane)carboxamide [(+)-KF4, (+)-5] as a novel chemotype possessing potent antagonist activity at the delta opioid receptor. Additional SAR studies involving changes to both the 2-amino and 7-amido N-substituents using this same (+)-morphan scaffold have revealed compounds with improved potency and selectivity for the delta opioid receptor. The highly potent and selective 2,2-dimethylphenylacetamide analogue (+)-N-[(1S,4R,5R,7S)-5-(3-hydroxyphenyl)-4-methyl-2-(3-phenylpropyl)-2-azabicyclo[3.3.1]non-7-yl]-2-methyl-2-phenylpropanamide (13d, delmorphan-A) showed picomolar inhibitory potency (Ke = 0.1 nM) in the [35S]GTPgammaS functional assay with delta opioid receptor selectivity ratios of 103- and 132-fold versus the mu and kappa opioid receptors, respectively. The compounds showed no agonist activity at any of the three opioid receptors; however, measurements of delta inverse agonist activity within this series illustrated a broad range of negative efficacy and IC50 values 650-fold more potent than the prototypical delta opioid receptor inverse agonist ICI 174,864 (22).

N-substituted 4beta-methyl-5-(3-hydroxyphenyl)-7alpha-amidomorphans are potent, selective kappa opioid receptor antagonists.

In a previous study, we identified (-)-N-[(1R,4S,5S,7R)-5-(3-hydroxyphenyl)-4-methyl-2-(3-phenylpropyl)-2-azabicyclo[3.3.1]non-7-yl]-3-(1-piperidinyl)propanamide (5a, KAA-1) as the first potent and selective kappa opioid receptor antagonist from the 5-(3-hydroxyphenyl)morphan class of opioids. In this study we report an improved synthesis of this class of compounds. The new synthetic method was used to prepare analogues 5b-r where the morphan N-substituent and 7alpha-amido group were varied. Most of the analogues showed sub-nanomolar potency for the kappa opioid receptor and were highly selective relative to the mu and delta opioid receptors. (-)-3-(3,4-Dihydroisoquinolin-2(1H)-yl)-N-{(1R,4S,5S,7R)-5-(3-hydroxyphenyl)-4-methyl-2-[2-(2-methylphenyl)ethyl]-2-azabicyclo[3.3.1]non-7-yl}propanamide (5n, MTHQ) is at least as potent and selective as nor-BNI as a kappa opioid receptor antagonist in the [35S]GTP-gamma-S in vitro functional test.