Positive allosteric modulators (PAMs) of the group II metabotropic glutamate receptors: Design, synthesis, and evaluation as ex-vivo tool compounds.

This letter describes synthesis and evaluation of two series of dual mGlu2/mGlu3 positive allosteric modulators with moderate mGlu3 potency and robust mGlu2 potency in thallium flux assays. These compounds were profiled their ability to modulate mGlu3-mediated signaling in central neurons by co-application of a selective mGlu2 NAM to isolate mGlu3-selective effects. Using acute mouse brain slices from the prefrontal cortex, potentiation of group II mGlu receptor agonist Ca2+ signaling in PFC pyramidal cells with either the dual mGlu2/mGlu3 PAM 16e or 23d demonstrated effects mediated selectively via mGlu3.

Discovery and optimization of a novel CNS penetrant series of mGlu4 PAMs based on a 1,4-thiazepane core with in vivo efficacy in a preclinical Parkinsonian model.

A high throughput screen (HTS) identified a novel, but weak (EC50 = 6.2 µM, 97% Glu Max) mGlu4 PAM chemotype based on a 1,4-thiazepane core, VU0544412. Reaction development and chemical optimization delivered a potent mGlu4 PAM VU6022296 (EC50 = 32.8 nM, 108% Glu Max) with good CNS penetration (Kp = 0.45, Kp,uu = 0.70) and enantiopreference. Finally, VU6022296 displayed robust, dose-dependent efficacy in reversing Haloperidol-Induced Catalepsy (HIC), a rodent preclinical Parkinson's disease model.

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 mGlu2/4 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 mGlu2/4 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 mGlu2/4 heterodimers; however, another compound displayed 75-fold preference for the mGlu2/2 homodimer over heterodimeric mGlu2/4 or homomeric mGlu4/4. 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 VU2957 (Valiglurax): An mGlu4 Positive Allosteric Modulator Evaluated as a Preclinical Candidate for the Treatment of Parkinson's Disease.

Herein, we report the discovery of a novel potent, selective, CNS penetrant, and orally bioavailable mGlu4 PAM, VU0652957 (VU2957, Valiglurax). VU2957 possessed attractive in vitro and in vivo pharmacological and DMPK properties across species. To advance toward the clinic, a spray-dried dispersion (SDD) formulation of VU2957 was developed to support IND-enabling toxicology studies. Based on its overall profile, VU2957 was evaluated as a preclinical development candidate for the treatment of Parkinson's disease.

Discovery, Structure-Activity Relationship, and Biological Characterization of a Novel Series of 6-((1 H-Pyrazolo[4,3- b]pyridin-3-yl)amino)-benzo[ d]isothiazole-3-carboxamides as Positive Allosteric Modulators of the Metabotropic Glutamate Receptor 4 (mGlu4).

This work describes the discovery and characterization of novel 6-(1 H-pyrazolo[4,3- b]pyridin-3-yl)amino-benzo[ d]isothiazole-3-carboxamides as mGlu4 PAMs. This scaffold provides improved metabolic clearance and CYP1A2 profiles compared to previously discovered mGlu4 PAMs. From this work, 27o (VU6001376) was identified as a potent (EC50 = 50.1 nM, 50.5% GluMax) and selective mGlu4 PAM with an excellent rat DMPK profile ( in vivo rat CLp = 3.1 mL/min/kg, t1/2 = 445 min, CYP1A2 IC50 > 30 µM). Compound 27o was also active in reversing haloperidol induced catalepsy in a rodent preclinical model of Parkinson's disease.

VU6010608, a Novel mGlu7 NAM from a Series of N-(2-(1H-1,2,4-Triazol-1-yl)-5-(trifluoromethoxy)phenyl)benzamides.

Herein, we report the structure-activity relationships within a series of mGlu7 NAMs based on an N-(2-(1H-1,2,4-triazol-1-yl)-5-(trifluoromethoxy)phenyl)benzamide core with excellent CNS penetration (Kp 1.9-5.8 and Kp,uu 0.4-1.4). Analogues in this series displayed steep SAR. Of these, VU6010608 (11a) emerged with robust efficacy in blocking high frequency stimulated long-term potentiation in electrophysiology studies.

Discovery of VU6005649, a CNS Penetrant mGlu7/8 Receptor PAM Derived from a Series of Pyrazolo[1,5-a]pyrimidines.

Herein, we report the structure-activity relationships within a series of mGlu7 PAMs based on a pyrazolo[1,5-a]pyrimidine core with excellent CNS penetration (Kps > 1 and Kp,uus > 1). Analogues in this series proved to display a range of Group III mGlu receptor selectivity, but VU6005649 emerged as the first dual mGlu7/8 PAM, filling a void in the Group III mGlu receptor PAM toolbox and demonstrating in vivo efficacy in a mouse contextual fear conditioning model.

Development and Antiparkinsonian Activity of VU0418506, a Selective Positive Allosteric Modulator of Metabotropic Glutamate Receptor 4 Homomers without Activity at mGlu2/4 Heteromers.

Metabotropic glutamate receptor 4 (mGlu4) is emerging as a potential therapeutic target for numerous central nervous system indications, including Parkinson's disease (PD). As the glutamate binding sites among the eight mGlu receptors are highly conserved, modulation of receptor activity via allosteric sites within the receptor transmembrane domains using positive and negative allosteric modulators (PAMs and NAMs, respectively) has become a common strategy. We and others have used PAMs targeting mGlu4 to show that potentiation of receptor signaling induces antiparkinsonian activity in a variety of PD animal models, including haloperidol-induced catalepsy and 6-hydroxydopamine-induced lesion. Recently, mGlu4 has been reported to form heteromeric complexes with other mGlu receptor subtypes, such as mGlu2, and the resulting heteromer exhibits a distinct pharmacological profile in response to allosteric modulators. For example, some mGlu4 PAMs do not appear to potentiate glutamate activity when mGlu2 and mGlu4 are coexpressed, whereas other compounds potentiate mGlu4 responses regardless of mGlu2 coexpression. We report here the discovery and characterization of VU0418506, a novel mGlu4 PAM with activity in rodent PD models. Using pharmacological approaches and Complemented Donor-Acceptor resonance energy transfer (CODA-RET) technology, we find that VU0418506 does not potentiate agonist-induced activity when mGlu2 and mGlu4 are heterodimerized, suggesting that the antiparkinsonian action of mGlu4 PAMs can be induced by compounds without activity at mGlu2/4 heteromers.

Discovery and characterization of a novel series of N-phenylsulfonyl-1H-pyrrole picolinamides as positive allosteric modulators of the metabotropic glutamate receptor 4 (mGlu4).

Herein we report the synthesis and characterization of a novel series of N-phenylsulfonyl-1H-pyrrole picolinamides as novel positive allosteric modulators of mGlu4. We detail our work towards finding phenyl replacements for the core scaffold of previously reported phenyl sulfonamides and phenyl sulfone compounds. Our efforts culminated in the identification of N-(1-((3,4-dimethylphenyl)sulfonyl)-1H-pyrrol-3-yl)picolinamide as a potent PAM of mGlu4.

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 106 (VU0650786) suitable for in vivo work. Compound 106 is a member of a series of 5-aryl-6,7-dihydropyrazolo[1,5-a]pyrazine-4(5H)-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 106 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.

Promoting peptide α-helix formation with dynamic covalent oxime side-chain cross-links.

Covalent side-chain cross-linking has been shown to be a viable strategy to control peptide folding. We report here that an oxime side-chain linkage can elicit α-helical folds from peptides in aqueous solution. The bio-orthogonal bridge is formed rapidly under neutral buffered conditions, and the resulting cyclic oximes are capable of dynamic covalent exchange.