A Novel Class of Succinimide-Derived Negative Allosteric Modulators of Metabotropic Glutamate Receptor Subtype 1 Provides Insight into a Disconnect in Activity between the Rat and Human Receptors

Recent progress in the discovery of mGlu₁ allosteric modulators has suggested the modulation of mGlu₁ could offer possible treatment for a number of central nervous system disorders; however, the available chemotypes are inadequate to fully investigate the therapeutic potential of mGlu₁ modulation. To address this issue, we used a fluorescence-based high-throughput screening assay to screen an allosteric modulator-biased library of compounds to generate structurally diverse mGlu₁ negative allosteric modulator hits for chemical optimization. Herein, we describe the discovery and characterization of a novel mGlu₁ chemotype. This series of succinimide negative allosteric modulators, exemplified by VU0410425, exhibited potent inhibitory activity at rat mGlu₁ but was, surprisingly, inactive at human mGlu₁. VU0410425 and a set of chemically diverse mGlu₁ negative allosteric modulators previously reported in the literature were utilized to examine this species disconnect between rat and human mGlu₁ activity. Mutation of the key transmembrane domain residue 757 and functional screening of VU0410425 and the literature compounds suggests that amino acid 757 plays a role in the activity of these compounds, but the contribution of the residue is scaffold specific, ranging from critical to minor. The operational model of allosterism was used to estimate the binding affinities of each compound to compare to functional data. This novel series of mGlu₁ negative allosteric modulators provides valuable insight into the pharmacology underlying the disconnect between rat and human mGlu₁ activity, an issue that must be understood to progress the therapeutic potential of allosteric modulators of mGlu₁

Discovery of (<i>R</i>)‑(2-Fluoro-4-((-4-methoxyphenyl)ethynyl)phenyl) (3-Hydroxypiperidin-1-yl)methanone (ML337), An mGlu₃ Selective and CNS Penetrant Negative Allosteric Modulator (NAM)

A multidimensional, iterative parallel synthesis effort identified a series of highly selective mGlu₃ NAMs with submicromolar potency and good CNS penetration. Of these, ML337 resulted (mGlu₃ IC₅₀ = 593 nM, mGlu₂ IC₅₀ >30 μM) with B:P ratios of 0.92 (mouse) to 0.3 (rat). DMPK profiling and shallow SAR led to the incorporation of deuterium atoms to address a metabolic soft spot, which subsequently lowered both in vitro and in vivo clearance by >50%

Substituted 1‑Phenyl-3-(pyridin-2-yl)urea Negative Allosteric Modulators of mGlu₅: Discovery of a New Tool Compound VU0463841 with Activity in Rat Models of Cocaine Addiction

Cocaine is a powerful and highly addictive stimulant that disrupts the normal reward circuitry in the central nervous system (CNS), producing euphoric effects. Cocaine use can lead to acute and life threatening emergencies, and abuse is associated with increased risk for contracting infectious diseases. Though certain types of behavioral therapy have proven effective for treatment of cocaine addiction, relapse remains high, and there are currently no approved medications for the treatment of cocaine abuse. Evidence has continued to accumulate that indicates a critical role for the metabotropic glutamate receptor subtype 5 (mGlu₅) in the modulation of neural circuitry associated with the addictive properties of cocaine. While the small molecule mGlu₅ negative allosteric modulator (NAM) field is relatively advanced, investigation into the potential of small molecule mGlu₅ NAMs for the treatment of cocaine addiction remains an area of high interest. Herein we describe the discovery and characterization of a potent and selective compound <b>29</b> (VU0463841) with good CNS exposure in rats. The utility of <b>29</b> (VU0463841) was demonstrated by its ability to attenuate drug seeking behaviors in relevant rat models of cocaine addiction

Design of 4‑Oxo-1-aryl-1,4-dihydroquinoline-3-carboxamides as Selective Negative Allosteric Modulators of Metabotropic Glutamate Receptor Subtype 2

Both orthosteric and allosteric antagonists of the group II metabotropic glutamate receptors (mGlus) have been used to establish a link between mGlu_2/3 inhibition and a variety of CNS diseases and disorders. Though these tools typically have good selectivity for mGlu_2/3 versus the remaining six members of the mGlu family, compounds that are selective for only one of the individual group II mGlus have proved elusive. Herein we report on the discovery of a potent and highly selective mGlu₂ negative allosteric modulator <b>58</b> (VU6001192) from a series of 4-oxo-1-aryl-1,4-dihydroquinoline-3-carboxamides. The concept for the design of this series centered on morphing a quinoline series recently disclosed in the patent literature into a chemotype previously used for the preparation of muscarinic acetylcholine receptor subtype 1 positive allosteric modulators. Compound <b>58</b> exhibits a favorable profile and will be a useful tool for understanding the biological implications of selective inhibition of mGlu₂ in the CNS

Design and Synthesis of mGlu₂ NAMs with Improved Potency and CNS Penetration Based on a Truncated Picolinamide Core

Herein, we detail the optimization of the mGlu₂ negative allosteric modulator (NAM), VU6001192, by a reductionist approach to afford a novel, simplified mGlu₂ NAM scaffold. This new chemotype not only affords potent and selective mGlu₂ inhibition, as exemplified by VU6001966 (mGlu₂ IC₅₀ = 78 nM, mGlu₃ IC₅₀ > 30 μM), but also excellent central nervous system (CNS) penetration (<i>K</i>_p = 1.9, <i>K</i>_p,uu = 0.78), a feature devoid in all previously disclosed mGlu₂ NAMs (<i>K</i>_ps ≈ 0.3, <i>K</i>_p,uus ≈ 0.1). Moreover, this series, based on overall properties, represents an exciting lead series for potential mGlu₂ PET tracer development

Discovery of Tricyclic Triazolo- and Imidazopyridine Lactams as M₁ Positive Allosteric Modulators

This Letter describes the chemical optimization of a new series of muscarinic acetylcholine receptor subtype 1 (M₁) positive allosteric modulators (PAMs) based on novel tricyclic triazolo- and imidazopyridine lactam cores, devoid of M₁ agonism, e.g., no M₁ ago-PAM activity, in high expressing recombinant cell lines. While all the new tricyclic congeners afforded excellent rat pharmacokinetic (PK) properties (CL_p < 8 mL/min/kg and <i>t</i>_1/2 > 5 h), regioisomeric triazolopyridine analogues were uniformly not CNS penetrant (<i>K</i>_p < 0.05), despite a lack of hydrogen bond donors. However, removal of a single nitrogen atom to afford imidazopyridine derivatives proved to retain the excellent rat PK and provide high CNS penetration (<i>K</i>_p > 2), despite inclusion of a basic nitrogen. Moreover, <b>24c</b> was devoid of M₁ agonism in high expressing recombinant cell lines and did not induce cholinergic seizures in vivo in mice. Interestingly, all of the new M₁ PAMs across the diverse tricyclic heterocyclic cores possessed equivalent CNS MPO scores (>4.5), highlighting the value of both “medicinal chemist’s eye” and experimental data, e.g., not sole reliance (or decision bias) on in silico calculated properties, for parameters as complex as CNS penetration

Identification of Specific Ligand–Receptor Interactions That Govern Binding and Cooperativity of Diverse Modulators to a Common Metabotropic Glutamate Receptor 5 Allosteric Site

A common metabotropic glutamate receptor 5 (mGlu₅) allosteric site is known to accommodate diverse chemotypes. However, the structural relationship between compounds from different scaffolds and mGlu₅ is not well understood. In an effort to better understand the molecular determinants that govern allosteric modulator interactions with mGlu₅, we employed a combination of site-directed mutagenesis and computational modeling. With few exceptions, six residues (P654, Y658, T780, W784, S808, and A809) were identified as key affinity determinants across all seven allosteric modulator scaffolds. To improve our interpretation of how diverse allosteric modulators occupy the common allosteric site, we sampled the wealth of mGlu₅ structure–activity relationship (SAR) data available by docking 60 ligands (actives and inactives) representing seven chemical scaffolds into our mGlu₅ comparative model. To spatially and chemically compare binding modes of ligands from diverse scaffolds, the ChargeRMSD measure was developed. We found a common binding mode for the modulators that placed the long axes of the ligands parallel to the transmembrane helices 3 and 7. W784 in TM6 not only was identified as a key NAM cooperativity determinant across multiple scaffolds, but also caused a NAM to PAM switch for two different scaffolds. Moreover, a single point mutation in TM5, G747V, altered the architecture of the common allosteric site such that 4-nitro-<i>N</i>-(1,3-diphenyl-1<i>H</i>-pyrazol-5-yl)­benzamide (VU29) was noncompetitive with the common allosteric site. Our findings highlight the subtleties of allosteric modulator binding to mGlu₅ and demonstrate the utility in incorporating SAR information to strengthen the interpretation and analyses of docking and mutational data

Discovery of a Selective and CNS Penetrant Negative Allosteric Modulator of Metabotropic Glutamate Receptor Subtype 3 with Antidepressant and Anxiolytic Activity in Rodents

Previous preclinical work has demonstrated the therapeutic potential of antagonists of the group II metabotropic glutamate receptors (mGlus). Still, compounds that are selective for the individual group II mGlus (mGlu₂ and mGlu₃) have been scarce. There remains a need for such compounds with the balance of properties suitable for convenient use in a wide array of rodent behavioral studies. We describe here the discovery of a selective mGlu₃ NAM <b>106</b> (VU0650786) suitable for in vivo work. Compound <b>106</b> is a member of a series of 5-aryl-6,7-dihydropyrazolo­[1,5-<i>a</i>]­pyrazine-4­(5<i>H</i>)-one compounds originally identified as a mGlu₅ positive allosteric modulator (PAM) chemotype. Its suitability for use in rodent behavioral models has been established by extensive in vivo PK studies, and the behavioral experiments presented here with compound <b>106</b> represent the first examples in which an mGlu₃ NAM has demonstrated efficacy in models where prior efficacy had previously been noted with nonselective group II antagonists

Discovery of <i>N</i>‑(5-Fluoropyridin-2-yl)-6-methyl-4-(pyrimidin-5-yloxy)picolinamide (VU0424238): A Novel Negative Allosteric Modulator of Metabotropic Glutamate Receptor Subtype 5 Selected for Clinical Evaluation

Preclinical evidence in support of the potential utility of mGlu₅ NAMs for the treatment of a variety of psychiatric and neurodegenerative disorders is extensive, and multiple such molecules have entered clinical trials. Despite some promising results from clinical studies, no small molecule mGlu₅ NAM has yet to reach market. Here we present the discovery and evaluation of <i>N</i>-(5-fluoropyridin-2-yl)-6-methyl-4-(pyrimidin-5-yloxy)­picolinamide (<b>27</b>, VU0424238), a compound selected for clinical evaluation. Compound <b>27</b> is more than 900-fold selective for mGlu₅ versus the other mGlu receptors, and binding studies established a <i>K</i>_i value of 4.4 nM at a known allosteric binding site. Compound <b>27</b> had a clearance of 19.3 and 15.5 mL/min/kg in rats and cynomolgus monkeys, respectively. Imaging studies using a known mGlu₅ PET ligand demonstrated 50% receptor occupancy at an oral dose of 0.8 mg/kg in rats and an intravenous dose of 0.06 mg/kg in baboons

Discovery of <i>N</i>‑(5-Fluoropyridin-2-yl)-6-methyl-4-(pyrimidin-5-yloxy)picolinamide (VU0424238): A Novel Negative Allosteric Modulator of Metabotropic Glutamate Receptor Subtype 5 Selected for Clinical Evaluation

Preclinical evidence in support of the potential utility of mGlu₅ NAMs for the treatment of a variety of psychiatric and neurodegenerative disorders is extensive, and multiple such molecules have entered clinical trials. Despite some promising results from clinical studies, no small molecule mGlu₅ NAM has yet to reach market. Here we present the discovery and evaluation of <i>N</i>-(5-fluoropyridin-2-yl)-6-methyl-4-(pyrimidin-5-yloxy)­picolinamide (<b>27</b>, VU0424238), a compound selected for clinical evaluation. Compound <b>27</b> is more than 900-fold selective for mGlu₅ versus the other mGlu receptors, and binding studies established a <i>K</i>_i value of 4.4 nM at a known allosteric binding site. Compound <b>27</b> had a clearance of 19.3 and 15.5 mL/min/kg in rats and cynomolgus monkeys, respectively. Imaging studies using a known mGlu₅ PET ligand demonstrated 50% receptor occupancy at an oral dose of 0.8 mg/kg in rats and an intravenous dose of 0.06 mg/kg in baboons