Identification of Neuropeptide S Antagonists: Structure–Activity Relationship Studies, X‑ray Crystallography, and in Vivo Evaluation

Modulation of the neuropeptide S (NPS) system has been linked to a variety of CNS disorders such as panic disorder, anxiety, sleeping disorders, asthma, obesity, PTSD, and substance abuse. In this study, a series of diphenyltetrahydro-1<i>H</i>-oxazolo­[3,4-α]­pyrazin-3­(5<i>H</i>)-ones were synthesized and evaluated for antagonist activity at the neuropeptide S receptor. The absolute configuration was determined by chiral resolution of the key synthetic intermediate, followed by analysis of one of the individual enantiomers by X-ray crystallography. The <i>R</i> isomer was then converted to a biologically active compound (<b>34</b>) that had a <i>K</i>_e of 36 nM. The most potent compound displayed enhanced aqueous solubility compared with the prototypical antagonist SHA-68 and demonstrated favorable pharmacokinetic properties for behavioral assessment. In vivo analysis in mice indicated a significant blockade of NPS induced locomotor activity at an ip dose of 50 mg/kg. This suggests that analogs having improved drug-like properties will facilitate more detailed studies of the neuropeptide S receptor system

Discovery of Novel Proline-Based Neuropeptide FF Receptor Antagonists

The neuropeptide FF (NPFF) system has been implicated in a number of physiological processes including modulating the pharmacological activity of opioid analgesics and several other classes of drugs of abuse. In this study, we report the discovery of a novel proline scaffold with antagonistic activity at the NPFF receptors through a high throughput screening campaign using a functional calcium mobilization assay. Focused structure–activity relationship studies on the initial hit <b>1</b> have resulted in several analogs with calcium mobilization potencies in the submicromolar range and modest selectivity for the NPFF1 receptor. Affinities and potencies of these compounds were confirmed in radioligand binding and functional cAMP assays. Two compounds, <b>16</b> and <b>33</b>, had good solubility and blood–brain barrier permeability that fall within the range of CNS permeant candidates without the liability of being a P-glycoprotein substrate. Finally, both compounds reversed fentanyl-induced hyperalgesia in rats when administered intraperitoneally. Together, these results point to the potential of these proline analogs as promising NPFF receptor antagonists

Effect of 1‑Substitution on Tetrahydroisoquinolines as Selective Antagonists for the Orexin‑1 Receptor

Selective blockade of the orexin-1 receptor (OX₁) has been suggested as a potential approach to drug addiction therapy because of its role in modulating the brain’s reward system. We have recently reported a series of tetrahydroisoquinoline-based OX₁ selective antagonists. Aimed at elucidating structure–activity relationship requirements in other regions of the molecule and further enhancing OX₁ potency and selectivity, we have designed and synthesized a series of analogues bearing a variety of substituents at the 1-position of the tetrahydroisoquinoline. The results show that an optimally substituted benzyl group is required for activity at the OX₁ receptor. Several compounds with improved potency and/or selectivity have been identified. When combined with structural modifications that were previously found to improve selectivity, we have identified compound <b>73</b> (RTIOX-251) with an apparent dissociation constant (<i>K</i>_e) of 16.1 nM at the OX₁ receptor and >620-fold selectivity over the OX₂ receptor. In vivo, compound <b>73</b> was shown to block the development of locomotor sensitization to cocaine in rats

Identification of 1‑({[1-(4-Fluorophenyl)-5-(2-methoxyphenyl)‑1<i>H</i>‑pyrazol-3-yl]carbonyl}amino)cyclohexane Carboxylic Acid as a Selective Nonpeptide Neurotensin Receptor Type 2 Compound

Compounds active at neurotensin receptors (NTS1 and NTS2) exert analgesic effects on different types of nociceptive modalities, including thermal, mechanical, and chemical stimuli. The NTS2 preferring peptide JMV-431 (<b>2</b>) and the NTS2 selective nonpeptide compound levocabastine (<b>6</b>) have been shown to be effective in relieving the pain associated with peripheral neuropathies. With the aim of identifying novel nonpeptide compounds selective for NTS2, we examined analogues of SR48692 (<b>5a</b>) using a FLIPR calcium assay in CHO cells stably expressing rat NTS2. This led to the discovery of the NTS2 selective nonpeptide compound 1-({[1-(4-fluorophenyl)-5-(2-methoxyphenyl)-1<i>H</i>-pyrazol-3-yl]­carbonyl}­amino)­cyclohexane carboxylic acid (NTRC-739, <b>7b</b>) starting from the nonselective compound <b>5a</b>

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

Identification of 2‑({[1-(4-Fluorophenyl)-5-(2-meth­oxy­phen­yl)‑1<i>H</i>‑pyr­azol-3-yl]­carb­onyl}ami­no)tri­cyclo[3.3.1.13,7]­dec­ane-2-carb­oxy­lic Acid (NTRC-844) as a Selective Antagonist for the Rat Neurotensin Receptor Type 2

Neurotensin receptor type 2 (NTS2) compounds display analgesic activity in animal pain models. We have identified the first high-affinity NTS2-selective antagonist (<b>8</b>) that is active in vivo. This study also revealed that the NTS2 FLIPR assay designation for a compound, agonist, partial agonist, and so forth, did not correlate with its in vivo activity as observed in the thermal tail-flick acute model of pain. This suggests that calcium mobilization is not the signaling pathway involved in NTS2-mediated analgesia as assessed by the thermal tail-flick model. Finally, we found a significant bias between rat and human for compound <b>9</b> in the NTS2 binding assay

Blocking Alcoholic Steatosis in Mice with a Peripherally Restricted Purine Antagonist of the Type 1 Cannabinoid Receptor

Type 1 cannabinoid receptor (CB1) antagonists have demonstrated promise for the treatment of obesity, liver disease, metabolic syndrome, and dyslipidemias. However, the inhibition of CB1 receptors in the central nervous system can produce adverse effects, including depression, anxiety, and suicidal ideation. Efforts are now underway to produce peripherally restricted CB1 antagonists to circumvent CNS-associated undesirable effects. In this study, a series of analogues were explored in which the 4-aminopiperidine group of compound <b>2</b> was replaced with aryl- and heteroaryl-substituted piperazine groups both with and without a spacer. This resulted in mildly basic, potent antagonists of human CB1 (hCB1). The 2-chlorobenzyl piperazine, <b>25</b>, was found to be potent (<i>K</i>_i = 8 nM); to be >1000-fold selective for hCB1 over hCB2; to have no hERG liability; and to possess favorable ADME properties including high oral absorption and negligible CNS penetration. Compound <b>25</b> was tested in a mouse model of alcohol-induced liver steatosis and found to be efficacious. Taken together, <b>25</b> represents an exciting lead compound for further clinical development or refinement