Synthesis and Nicotinic Acetylcholine Receptor in Vitro and in Vivo Pharmacological Properties of 2′-Fluoro-3′-(substituted phenyl)deschloroepibatidine Analogues of 2′-Fluoro-3′-(4-nitrophenyl)deschloroepibatidine

Herein, we report the synthesis and nicotinic acetylcholine receptor (nAChR) in vitro and in vivo pharmacological properties of 2′-fluoro-3′-(substituted phenyl)­deschloroepibatidines <b>5b</b>–<b>g</b>, analogues of 3′-(4-nitrophenyl) compound <b>5a</b>. All compounds had high affinity for α4β2-nAChR and low affinity for α7-nAChR. Initial electrophysiological studies showed that all analogues were antagonists at α4β2-, α3β4-, and α7-nAChRs. The 4-carbamoylphenyl analogue <b>5g</b> was highly selective for α4β2-nAChR over α3β4- and α7-nAChRs. All the analogues were antagonists of nicotine-induced antinociception in the tail-flick test. Molecular modeling docking studies using the agonist-bound form of the X-ray crystal structure of the acetylcholine binding protein suggested several different binding modes for epibatidine, varenicline, and <b>5a</b>–<b>g</b>. In particular, a unique binding mode for <b>5g</b> was suggested by these docking simulations. The high binding affinity, in vitro efficacy, and selectivity of <b>5g</b> for α4β2-nAChR combined with its nAChR functional antagonist properties suggest that <b>5g</b> will be a valuable pharmacological tool for studying the nAChR and may have potential as a pharmacotherapy for addiction and other central nervous system disorders

Synthesis and Evaluation of Metabotropic Glutamate Receptor Subtype 5 Antagonists Based on Fenobam

In an effort to discover potent and selective metabotropic glutamate receptor subtype 5 (mGluR5) antagonists, 15 tetrahydropyrimidinone analogues of 1-(3-chlorophenyl)-3-(1-methyl-4-oxo-4,5-dihydro-1<i>H</i>-imidazol-2-yl)-urea (fenobam) were synthesized. These compounds were evaluated for antagonism of glutamate-mediated mobilization of internal calcium in an mGluR5 in vitro efficacy assay. The IC₅₀ value for 1-(3-chlorophenyl)-3-(1-methyl-4-oxo-1,4,5,6-tetrahydropyridine)­urea (<b>4g</b>) was essentially identical to that of fenobam

Synthesis, Nicotinic Acetylcholine Receptor Binding, and Antinociceptive Properties of 2′-Fluoro-3′-(substituted pyridinyl)-7-deschloroepibatidine Analogues

2′-Fluoro-3-(substituted pyridine)­epibatidine analogues <b>7a</b>–<b>e</b> and <b>8a</b>–<b>e</b> were synthesized, and their in vitro and in vivo nAChR properties were determined. 2′-Fluoro-3′-(4″-pyridinyl)­deschloroepibatidine (<b>7a</b>) and 2′-fluoro-3′-(3″-pyridinyl)­deschloroepibatidine (<b>8a</b>) were synthesized as bioisosteres of the 4′-nitrophenyl lead compounds <b>5a</b> and <b>5g</b>. Comparison of the in vitro nAChR properties of <b>7a</b> and <b>8a</b> to those of <b>5a</b> and <b>5g</b> showed that <b>7a</b> and <b>8a</b> had in vitro nAChR properties similar to those of <b>5a</b> and <b>5g</b> but both were more selective for the α4β2-nAChR relative to the α3β4- and α7-nAChRs than <b>5a</b> and <b>5g</b>. The in vivo nAChR properties in mice of <b>7a</b> were similar to those of <b>5a</b>. In contrast, <b>8a</b> was an agonist in all four mouse acute tests, whereas <b>5g</b> was active only in a spontaneous activity test. In addition, <b>5g</b> was a nicotine antagonist in both the tail-flick and hot-plate tests, whereas <b>8a</b> was an antagonist only in the tail-flick test

4β-Methyl-5-(3-hydroxyphenyl)morphan Opioid Agonist and Partial Agonist Derived from a 4β-Methyl-5-(3-hydroxyphenyl)morphan Pure Antagonist

In previous studies we reported that addition of 7α-acylamino groups to <i>N</i>-phenylpropyl-4β-methyl-5-(3-hydroxyphenyl)­morphan (<b>4</b>) led to compounds that were pure opioid receptor antagonists. In contrast to these findings we report in this study that addition of a 7α-amino (<b>5a</b>), 7α-alkylamino (<b>5b</b>–<b>e</b>), or 7α-dialkylamino (<b>5f</b>–<b>h</b>) group to <b>4</b> leads to opioid receptor ligands with varying degrees of agonist/antagonist activity. The 7α-amino and 7α-methylamino analogues were full agonists at the μ and δ receptors and antagonists at the κ receptor. The 7α-cyclopropylmethylamino analogue <b>5h</b> was a full agonist at the μ receptor with weaker agonist activity at the δ and κ receptors. Whereas the addition of a 7α-acylamino group to the pure nonselective opioid receptor antagonist <i>N</i>-phenylpropyl-4β-methyl-5-(3-hydroxyphenyl)­morphan (<b>4</b>) led to κ selective pure opioid receptor antagonist, the addition of a 7α-amino, 7α-alkylamino, or 7α-dialkylamino group to <b>4</b> leads to opioid ligands that are largely μ or δ agonist with mixed agonist/antagonist properties

Design, Synthesis, and Biological Evaluation of Structurally Rigid Analogues of 4‑(3-Hydroxy­phenyl)­piperidine Opioid Receptor Antagonists

In order to gain additional information concerning the active conformation of the <i>N</i>-substituted <i>trans</i>-3,4-dimethyl-4-(3-hydroxy­phenyl)­piperidine (<b>1</b>) class of opioid receptor antagonists, procedures were developed for the synthesis of structurally rigid <i>N</i>-substituted-6-(3-hydroxy­phenyl)­3-azabicyclo­[3.1.0]­hexane and 3-methyl-4-(3-hydroxy­phenyl)-4-azabicyclo­[4.1.0]­heptanes. Evaluation of the conformationally constrained series in a [³⁵S]­GTPγS assay showed that structural rigid compounds having the 3-hydroxyphenyl group locked in the piperidine equatorial orientation had potencies equal to or better than similar compounds having more flexible structures similar to <b>1</b>. The studies of the rigid compounds also suggested that the 3-methyl group present in compound <b>1</b> type antagonists may not be necessary for their pure opioid antagonist properties

Caged Naloxone: Synthesis, Characterization, and Stability of 3‑<i>O</i>‑(4,5-Dimethoxy-2-nitrophenyl)carboxymethyl Naloxone (CNV-NLX)

The photolabile analogue of the broad-spectrum opioid antagonist naloxone, 3-<i>O</i>-(4,5-dimethoxy-2-nitrophenyl)­carboxymethyl naloxone (also referred to as “caged naloxone”, 3-<i>O</i>-(α-carboxy-6-nitroveratryl)­naloxone, CNV-NLX), has been found to be a valuable biochemical probe. While the synthesis of CNV-NLX is simple, its characterization is complicated by the fact that it is produced as a mixture of α<i>R</i>,5<i>R</i>,9<i>R</i>,13<i>S</i>,14<i>S</i> and α<i>S</i>,5<i>R</i>,9<i>R</i>,13<i>S</i>,14<i>S</i> diastereomers. Using long-range and heteronuclear NMR correlations, the ¹H NMR and ¹³C NMR resonances of both diastereomers have been fully assigned, confirming the structures. Monitoring of solutions of CNV-NLX in saline buffer, in methanol, and in DMSO has shown CNV-NLX to be stable for over a week under fluorescent laboratory lights at room temperature. Exposure of such solutions to λ 365 nm from a hand-held UV lamp led to the formation of naloxone and CNV-related breakdown products

Discovery of <i>N</i>‑{4-[(3-Hydroxyphenyl)-3-methylpiperazin-1-yl]methyl-2-methylpropyl}-4-phenoxybenzamide Analogues as Selective Kappa Opioid Receptor Antagonists

There is continuing interest in the discovery and development of new κ opioid receptor antagonists. We recently reported that N-substituted 3-methyl-4-(3-hydroxyphenyl)­piperazines were a new class of opioid receptor antagonists. In this study, we report the syntheses of two piperazine JDTic-like analogues. Evaluation of the two compounds in an in vitro [³⁵S]­GTPγS binding assay showed that neither compound showed the high potency and κ opioid receptor selectivity of JDTic. A library of compounds using the core scaffold <b>21</b> was synthesized and tested for their ability to inhibit [³⁵S]­GTPγS binding stimulated by the selective κ opioid agonist U69,593. These studies led to <i>N</i>-[(1<i>S</i>)-1-{[(3<i>S</i>)-4-(3-hydroxyphenyl)-3-methylpiperazin-1-yl]­methyl}-2-methylpropyl]-4-phenoxybenzamide (<b>11a</b>), a compound that showed good κ opioid receptor antagonist properties. An SAR study based on <b>11a</b> provided 28 novel analogues. Evaluation of these 28 compounds in the [³⁵S]­GTPγS binding assay showed that several of the analogues were potent and selective κ opioid receptor antagonists

Novel Synthesis and Pharmacological Characterization of NOP Receptor Agonist 8-[(1<i>S</i>,3a<i>S</i>)-2,3,3a,4,5,6-Hexahydro-1<i>H</i>-phenalen-1-yl]-1-phenyl-1,3,8-triazaspiro[4.5]decan-4-one (Ro 64-6198)

The nociceptin/orphanin FQ opioid peptide (NOP) receptor is a widely expressed GPCR involved in the modulation of pain, anxiety, and motor behaviors. Dissecting the functional properties of this receptor is limited by the lack of systemically active ligands that are brain permeant. The small molecule NOP receptor-selective, full agonist 8-[(1<i>S</i>,3a<i>S</i>)-2,3,3a,4,5,6-hexahydro-1<i>H</i>-phenalen-1-yl]-1-phenyl-1,3,8-triazaspiro[4.5]decan-4-one (Ro 64-6198) hydrochloride is an active, brain penetrant ligand, but its difficult and cost-prohibitive synthesis limits its widespread use and availability for animal studies. Here, we detail a more efficient and convenient method of synthesis, and use both in vitro and in vivo pharmacological assays to fully characterize this ligand. Specifically, we characterize the pharmacodynamics of Ro 64-6198 in cAMP and G-protein coupling in vitro and examine, for the first time, the effects of nociceptin/orphanin FQ and Ro 64-6198 in arrestin recruitment assays. Further, we examine the effects of Ro 64-6198 on analgesia, anxiety, and locomotor responses in vivo. This new synthesis and pharmacological characterization provide additional insights into the useful, systemically active, NOP receptor agonist Ro 64-6198