Discovery of imidazo[1,2-a]-, [1,2,4]triazolo[4,3-a]-, and [1,2,4]triazolo[1,5-a]pyridine-8-carboxamide negative allosteric modulators of metabotropic glutamate receptor subtype 5

Based on a hypothesis that an intramolecular hydrogen bond was present in our lead series of picolinamide mGlu₅ NAMs, we reasoned that an inactive nicotinamide series could be modified through introduction of a fused heterocyclic core to generate potent mGlu₅ NAMs. In this Letter, we describe the synthesis and evaluation of compounds that demonstrate the viability of that approach. Selected analogs were profiled in a variety of in vitro assays, and two compounds were evaluated in rat pharmacokinetic studies and a mouse model of obsessive-compulsive disorder. Ancillary pharmacology screening revealed that members of this series exhibited moderate inhibition of the dopamine transporter (DAT), and SAR was developed that expanded the selectivity for mGlu₅ versus DAT.     

Discovery of molecular switches within the ADX-47273 mGlu5 PAM scaffold that modulate modes of pharmacology to afford potent mGlu5 NAMs, PAMs and partial antagonists

This Letter describes a chemical lead optimization campaign directed at a weak mGlu₅ NAM discovered while developing SAR for the mGlu₅ PAM, ADX-47273. An iterative parallel synthesis effort discovered multiple, subtle molecular switches that afford potent mGlu₅ NAMs, mGlu₅ PAMs as well as mGlu₅ partial antagonists.     

Discovery of VU0409106: A negative allosteric modulator of mGlu5 with activity in a mouse model of anxiety

Development of SAR in an aryl ether series of mGlu₅ NAMs leading to the identification of tool compound VU0409106 is described in this Letter. VU0409106 is a potent and selective negative allosteric modulator of mGlu₅ that binds at the known allosteric binding site and demonstrates good CNS exposure following intraperitoneal dosing in mice. VU0409106 also proved efficacious in a mouse marble burying model of anxiety, an assay known to be sensitive to mGlu₅ antagonists as well as clinically efficacious anxiolytics.     

Further exploration of an N-aryl phenoxyethoxy pyridinone-based series of mGlu3 NAMs: Challenging SAR,enantiospecific activity and in vivo efficacy

This letter describes the further optimization of a series of mGlu₃ NAMs based on an N-aryl phenoxyethoxy pyridinone core. A multidimensional optimization campaign, with focused matrix libraries, quickly established challenging SAR, enantiospecific activity, differences in assay read-outs (Ca²⁺ flux via a promiscuous G protein (G_α15) versus native coupling to GIRK channels), identified both full and partial mGlu₃ NAMs and a new in vivo tool compound, VU6017587. This mGlu₃ NAM showed efficacy in tail suspension, elevated zero maze and marble burying, suggesting selective inhibition of mGlu₃ affords anxiolytic-like and antidepressant-like phenotypes in mice.     

Synthesis and SAR of substituted pyrazolo[1,5-a]quinazolines as dual mGlu2/mGlu3 NAMs

Herein we report the design and synthesis of a series of substituted pyrazolo[1,5-a]quinazolin-5(4H)-ones as negative allosteric modulators of metabotropic glutamate receptors 2 and 3 (mGlu₂ and mGlu₃, respectively). Development of this series was initiated by reports that pyrazolo[1,5-a]quinazoline-derived scaffolds can yield compounds with activity at group II mGlu receptors which are prone to molecular switching following small structural changes. Several potent analogues, including 4-methyl-2-phenyl-8-(pyrimidin-5-yl)pyrazolo[1,5-a]quinazolin-5(4H)-one (10b), were discovered with potent in vitro activity as dual mGlu₂/mGlu₃ NAMs, with excellent selectivity versus the other mGluRs.     

Surveying heterocycles as amide bioisosteres within a series of mGlu7 NAMs: Discovery of VU6019278

This letter describes a diversity-oriented library approach to rapidly assess diverse heterocycles as bioisosteric replacements for a metabolically labile amide moiety within a series of mGlu₇ negative allosteric modulators (NAMs). SAR rapidly honed in on either a 1,2,4- or 1,3,4-oxadizaole ring system as an effective bioisostere for the amide. Further optimization of the southern region of the mGlu₇ NAM chemotype led to the discovery of VU6019278, a potent mGlu₇ NAM (IC₅₀?=?501?nM, 6.3% L-AP₄ Min) with favorable plasma protein binding (rat f_u?=?0.10), low predicted hepatic clearance (rat CL_hep?=?27.7?mL/min/kg) and high CNS penetration (rat K_p?=?4.9, K_p,uu?=?0.65).     

Synthesis and pharmacological evaluation of bivalent tethered ligands to target the mGlu2/4 heterodimeric receptor results in a compound with mGlu2/2 homodimer selectivity

This Letter details our ongoing efforts to develop selective positive allosteric modulators (PAMs) of the mGlu_2/4 heterodimeric receptor that exists in the CNS and may represent a novel drug target to modulate the glutamatergic system. As multiple hit-to-lead campaigns from HTS hits failed to produce selective small molecule mGlu_2/4 heterodimer PAMs, we were inspired by the work of Portoghese to synthesize and evaluate a set of nine bivalent tethered ligands (possessing an mGlu₂ PAM at one terminus and an mGlu₄ PAM at the other). Utilizing G protein-Inwardly Rectifying Potassium (GIRK) channel functional assays, we found that the tethered ligands displayed PAM activity in a cell line co-expressing both mGlu₂ and mGlu₄ but also in cells expressing mGlu₂ or mGlu₄ alone. In a CODA-RET assay, one of the tethered ligands potentiated mGlu_2/4 heterodimers; however, another compound displayed 75-fold preference for the mGlu_2/2 homodimer over heterodimeric mGlu_2/4 or homomeric mGlu_4/4. This work highlights the development of mGlu receptor PAMs with homodimer/heterodimer preference and expands the potential for PAMs as tethered ligands beyond the more classical antagonists and NAMs.     

Discovery of VU0431316: A negative allosteric modulator of mGlu5 with activity in a mouse model of anxiety

Development of SAR in an aryl ether series of mGlu₅ NAMs leading to the identification of pyrazine analog VU0431316 is described in this Letter. VU0431316 is a potent and selective non-competitive antagonist of mGlu₅ that binds at a known allosteric binding site. VU0431316 demonstrates an attractive DMPK profile, including moderate clearance and good bioavailability in rats. Intraperitoneal (IP) dosing of VU0431316 in a mouse marble burying model of anxiety, an assay known to be sensitive to mGlu₅ antagonists and other anxiolytics, produced dose proportional effects.     

Fused thiazolyl alkynes as potent mGlu5 receptor positive allosteric modulators

A new series of potent fused thiazole mGlu₅ receptor positive allosteric modulators (PAMs) (10, 11 and 27–31) are disclosed and details of the SAR and optimization are described. Optimization of alkynyl thiazole 9 (Lu AF11205) led to the identification of potent fused thiazole analogs 10b, 27a, 28j and 31d. In general, substituted cycloalkyl, aryl and heteroaryl carboxamides, and carbamate analogs are mGlu₅ PAMs, whereas smaller alkyl carboxamide, sulfonamide and sulfamide analogs tend to be mGlu₅ negative allosteric modulators (NAMs).     

Discovery of novel positive allosteric modulators of the metabotropic glutamate receptor 5 (mGlu5)

Novel in vitro mGlu₅ positive allosteric modulators with good potency, solubility, and low lipophilicity are described. Compounds were identified which did not rely on the phenylacetylene and carbonyl functionalities previously observed to be required for in vitro activity. Investigation of the allosteric binding requirements of a series of dihydroquinolinone analogs led to phenylacetylene azachromanone 4 (EC₅₀ 11.5 nM). Because of risks associated with potential metabolic and toxicological liabilities of the phenylacetylene, this moiety was successfully replaced with a phenoxymethyl group (27; EC₅₀ 156.3 nM). Derivation of a second-generation of mGlu₅ PAMs lacking a ketone carbonyl resulted in azaindoline (33), azabenzimidazole (36), and N-methyl 8-azaoxazine (39) phenylacetylenes. By scoping nitrogen substituents and phenylacetylene replacements in 39, we identified phenoxymethyl 8-azaoxazine 47 (EC₅₀ 50.1 nM) as a potent and soluble mGlu₅ PAM devoid of both undesirable phenylacetylene and carbonyl functionalities.     

Discovery of 4-alkoxy-6-methylpicolinamide negative allosteric modulators of metabotropic glutamate receptor subtype 5

This letter describes the further chemical optimization of VU0424238 (auglurant), an mGlu₅ NAM clinical candidate that failed in non-human primate (NHP) 28?day toxicology due to accumulation of a species-specific aldehyde oxidase (AO) metabolite of the pyrimidine head group. Here, we excised the pyrimidine moiety, identified the minimum pharmacophore, and then developed a new series of saturated ether head groups that ablated any AO contribution to metabolism. Putative back-up compounds in this novel series provided increased sp³ character, uniform CYP₄₅₀-mediated metabolism across species, good functional potency and high CNS penetration. Key to the optimization was a combination of matrix and iterative libraries that allowed rapid surveillance of multiple domains of the allosteric ligand.     

Synthesis and SAR of novel, 4-(phenylsulfamoyl)phenylacetamide mGlu4 positive allosteric modulators (PAMs) identified by functional high-throughput screening (HTS)

Herein we disclose the synthesis and SAR of a series of 4-(phenylsulfamoyl)phenylacetamide compounds as mGlu₄ positive allosteric modulators (PAMs) that were identified via a functional HTS. An iterative parallel approach to these compounds culminated in the discovery of VU0364439 (11) which represents the most potent (19.8 nM) mGlu₄ PAM reported to date.     

Discovery and SAR of a novel series of metabotropic glutamate receptor 5 positive allosteric modulators with high ligand efficiency

We report the optimization of a series of novel metabotropic glutamate receptor 5 (mGlu₅) positive allosteric modulators (PAMs) from a 5,6-bicyclic class of dihydropyrazolo[1,5-a]pyridin-4(5H)-ones containing a phenoxymethyl linker. Studies focused on a survey of non-amide containing hydrogen bond accepting (HBA) pharmacophore replacements. A highly potent and selective PAM, 2-(phenoxymethyl)-6,7-dihydropyrazolo[1,5-a]pyridin-4(5H)-one (11, VU0462054), bearing a simple ketone moiety, was identified (LE = 0.52, LELP = 3.2). In addition, hydroxyl, difluoro, ether, and amino variations were examined. Despite promising lead properties and exploration of alternative core heterocycles, linkers, and ketone replacements, oxidative metabolism and in vivo clearance remained problematic for the series.     

New 1,2,4-oxadiazole derivatives with positive mGlu4 receptor modulation activity and antipsychotic-like properties

Considering the allosteric regulation of mGlu receptors for potential therapeutic applications, we developed a group of 1,2,4-oxadiazole derivatives that displayed mGlu₄ receptor positive allosteric modulatory activity (EC₅₀ = 282–656 nM). Selectivity screening revealed that they were devoid of activity at mGlu₁, mGlu₂ and mGlu₅ receptors, but modulated mGlu₇ and mGlu₈ receptors, thus were classified as group III-preferring mGlu receptor agents. None of the compounds was active towards hERG channels or in the mini-AMES test. The most potent in vitro mGlu₄ PAM derivative 52 (N-(3-chloro-4-(5-(2-chlorophenyl)-1,2,4-oxadiazol-3-yl)phenyl)picolinamide) was readily absorbed after i.p. administration (male Albino Swiss mice) and reached a maximum brain concentration of 949.76 ng/mL. Five modulators (34, 37, 52, 60 and 62) demonstrated significant anxiolytic- and antipsychotic-like properties in the SIH and DOI-induced head twitch test, respectively. Promising data were obtained, especially for N-(4-(5-(2-chlorophenyl)-1,2,4-oxadiazol-3-yl)-3-methylphenyl)picolinamide (62), whose effects in the DOI-induced head twitch test were comparable to those of clozapine and better than those reported for the selective mGlu₄ PAM {"type":"entrez-protein","attrs":{"text":"ADX88178","term_id":"323512724"}}ADX88178.     

Discovery and SAR of a novel series of non-MPEP site mGlu5 PAMs based on an aryl glycine sulfonamide scaffold

Herein we report the discovery and SAR of a novel series of non-MPEP site metabotropic glutamate receptor 5 (mGlu₅) positive allosteric modulators (PAMs) based on an aryl glycine sulfonamide scaffold. This series represents a rare non-MPEP site mGlu₅ PAM chemotype.     

3-(Pyridin-2-yl-ethynyl)benzamide metabotropic glutamate receptor 5 negative allosteric modulators: hit to lead studies

A series of 3-(pyridin-2-yl-ethynyl)benzamide negative allosteric modulators of the metabotropic glutamate receptor 5 (mGluR5 NAMs) have been prepared. Starting from HTS hit 1 (IC₅₀: 926 nM), potent mGluR5 NAMs showing excellent potencies (IC₅₀s <50 nM) and good physicochemical profiles were prepared by monitoring LipE values. One compound 26 showed excellent mGluR5 binding (K_i: 21 nM) and antagonism (IC₅₀: 8 nM), an excellent rat PK profile (CL: 12 mL/min/kg, %F: 85) and showed oral activity in a mouse 4-Plate Behavioral model of anxiety (MED: 30 mpk) and a mouse Stress Induced Hyperthermia model of anxiety (MED 17.8 mpk).     

Radiosynthesis of N-(4-chloro-3-[11C]methoxyphenyl)-2-picolinamide ([11C]ML128) as a PET radiotracer for metabotropic glutamate receptor subtype 4 (mGlu4)

N-(Chloro-3-methoxyphenyl)-2-picolinamide (3, ML128, VU0361737) is an mGlu₄ positive allosteric modulator (PAM), which is potent and centrally penetrating. 3 is also the first mGlu₄ PAM to show efficacy in a preclinical Parkinson disease model upon systemic dosing. As a noninvasive medical imaging technique and a powerful tool in neurological research, positron emission tomography (PET) offers a possibility to investigate mGlu₄ expression in vivo under physiologic and pathological conditions. We synthesized a carbon-11 labeled ML128 ([¹¹C]3) as a PET radiotracer for mGlu₄, and characterized its biological properties in Sprague Dawley rats. [¹¹C]3 was synthesized from N-(4-chloro-3-hydroxyphenyl)-2-picolinamide (2) using [¹¹C]CH₃I. Total synthesis time was 38 ± 2.2 min (n = 7) from the end of bombardment to the formulation. The radioligand [¹¹C]3 was obtained in 27.7 ± 5.3% (n = 5) decay corrected radiochemical yield based on the radioactivity of [¹¹C]CO₂. The radiochemical purity of [¹¹C]3 was >99%. Specific activity was 188.7 ± 88.8 GBq/mol (n = 4) at the end of synthesis (EOS).PET images were conducted in 20 normal male Sprague Dawley rats including 11 control studies, 6 studies blocking with an mGlu₄ modulator (4) to investigate specificity and 3 studies blocking with an mGlu₅ modulator (MTEP) to investigate selectivity. These studies showed fast accumulation of [¹¹C]3 (peak activity between 1–3 min) in several brain areas including striatum, thalamus, hippocampus, cerebellum, and olfactory bulb following with fast washout. Blocking studies with the mGlu₄ modulator 4 showed 22–28% decrease of [¹¹C]3 accumulation while studies of selectivity showed only minor decrease supporting good selectivity over mGlu₅. Biodistribution studies and blood analyses support fast metabolism. Altogether this is the first PET imaging ligand for mGlu₄, in which the labeled ML128 was used for imaging its in vivo distribution and pharmacokinetics in brain.     

Discovery of (1R,2R)-N-(4-(6-isopropylpyridin-2-yl)-3-(2-methyl-2H-indazol-5-yl)isothiazol-5-yl)-2-methylcyclopropanecarboxamide,a potent and orally efficacious mGlu5 receptor negative allosteric modulator

A novel series of selective negative allosteric modulators (NAMs) for metabotropic glutamate receptor 5 (mGlu5) was discovered from an isothiazole scaffold. One compound of this series, (1R,2R)-N-(4-(6-isopropylpyridin-2-yl)-3-(2-methyl-2H-indazol-5-yl)isothiazol-5-yl)-2-methylcyclopropanecarboxamide (24), demonstrated satisfactory pharmacokinetic properties and, following oral dosing in rats, produced dose-dependent and long-lasting mGlu5 receptor occupancy. Consistent with the hypothesis that blockade of mGlu5 receptors will produce analgesic effects in mammals, compound 24 produced a dose-dependent reduction in paw licking responses in the formalin model of persistent pain.     

Discovery and SAR of 6-substituted-4-anilinoquinazolines as non-competitive antagonists of mGlu5

A high-throughput cell-based screen identified a series of 6-substituted-4-anilinoquinazolines as non-competitive antagonists of metabotropic glutamate receptor 5 (mGlu₅). This Letter describes the SAR of this series and the profile of selected compounds in selectivity and radioligand binding assays.     

Synthesis and SAR of a series of mGlu7 NAMs based on an ethyl-8-methoxy-4-(4-phenylpiperazin-1-yl)quinoline carboxylate core

A High-Throughput Screening (HTS) campaign identified a fundamentally new mGlu₇ NAM chemotype, based on an ethyl-8-methoxy-4-(4-phenylpiperazin-1-yl)quinolone carboxylate core. The initial hit, VU0226390, was a potent mGlu₇ NAM (IC₅₀ = 647 nM, 6% L-AP4 min) with selectivity versus the other group III mGlu receptors (>30 μM vs. mGlu₄ and mGlu₈). A multi-dimensional optimization effort surveyed all regions of this new chemotype, and found very steep SAR, reminiscent of allosteric modulators, and unexpected piperazine mimetics (whereas classical bioisosteres failed). While mGlu₇ NAM potency could be improved (IC₅₀s ~ 350 nM), the necessity of the ethyl ester moiety and poor physiochemical and DMPK properties precluded optimization towards in vivo tool compounds or clinical candidates. Still, this hit-to-lead campaign afforded key medicinal chemistry insights and new opportunities.