Discovery of VU6007496: Challenges in the Development of an M1 Positive Allosteric Modulator Backup Candidate.

Herein we report progress toward a backup clinical candidate to the M1 positive allosteric modulator (PAM) VU319/ACP-319. Scaffold-hopping from the pyrrolo[2,3-b]pyridine-based M1 PAM VU6007477 to isomeric pyrrolo[3,2-b]pyridine and thieno[3,2-b]pyridine congeners identified several backup contenders. Ultimately, VU6007496, a pyrrolo[3,2-b]pyridine, advanced into late stage profiling, only to be plagued with unanticipated, species-specific metabolism and active/toxic metabolites which were identified in our phenotypic seizure liability in vivo screen, preventing further development. However, VU6007496 proved to be a highly selective and CNS penetrant M1 PAM, with minimal agonism, that displayed excellent multispecies IV/PO pharmacokinetics (PK), CNS penetration, no induction of long-term depression (or cholinergic toxicity) and robust efficacy in novel object recognition (minimum effective dose = 3 mg/kg p.o.). Thus, VU6007496 can serve as another valuable in vivo tool compound in rats and nonhuman primates, but not mouse, to study selective M1 activation.

Discovery of VU6028418: A Highly Selective and Orally Bioavailable M4 Muscarinic Acetylcholine Receptor Antagonist.

Herein, we report the SAR leading to the discovery of VU6028418, a potent M4 mAChR antagonist with high subtype-selectivity and attractive DMPK properties in vitro and in vivo across multiple species. VU6028418 was subsequently evaluated as a preclinical candidate for the treatment of dystonia and other movement disorders. During the characterization of VU6028418, a novel use of deuterium incorporation as a means to modulate CYP inhibition was also discovered.

SAR inspired by aldehyde oxidase (AO) metabolism: Discovery of novel, CNS penetrant tricyclic M4 PAMs.

This letter describes progress towards an M4 PAM preclinical candidate inspired by an unexpected aldehyde oxidase (AO) metabolite of a novel, CNS penetrant thieno[2,3-c]pyridine core to an equipotent, non-CNS penetrant thieno[2,3-c]pyrdin-7(6H)-one core. Medicinal chemistry design efforts yielded two novel tricyclic cores that enhanced M4 PAM potency, regained CNS penetration, displayed favorable DMPK properties and afforded robust in vivo efficacy in reversing amphetamine-induced hyperlocomotion in rats.

VU6005806/AZN-00016130, an advanced M4 positive allosteric modulator (PAM) profiled as a potential preclinical development candidate.

This letter describes progress towards an M4 PAM preclinical candidate that resulted in the discovery of VU6005806/AZN-00016130. While the thieno[2,3-c]pyridazine core has been a consistent feature of key M4 PAMs, no work had previously been reported with respect to alternate functionality at the C3 position of the pyridazine ring. Here, we detail new chemistry and analogs that explored this region, and quickly led to VU6005806/AZN-00016130, which was profiled as a putative candidate. While, the ß-amino carboxamide moiety engendered solubility limited absorption in higher species precluding advancement (or requiring extensive pharmaceutical sciences formulation), VU6005806/AZN-00016130 represents a new, high quality preclinical in vivo probe.

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.

Novel M4 positive allosteric modulators derived from questioning the role and impact of a presumed intramolecular hydrogen-bonding motif in ß-amino carboxamide-harboring ligands.

This letter describes a focused exercise to explore the role of the ß-amino carboxamide moiety found in all of the first generation M4 PAMs and question if the NH2 group served solely to stabilize an intramolecular hydrogen bond (IMHB) and enforce planarity. To address this issue (and to potentially find a substitute for the ß-amino carboxamide that engendered P-gp and contributed to solubility liabilities), we removed the NH2, generating des-amino congeners and surveyed other functional groups in the ß-position. These modifications led to weak M4 PAMs with poor DMPK properties. Cyclization of the ß-amino carboxamide moiety by virtue of a pyrazole ring re-enforced the IMHB, led to potent (and patented) M4 PAMs, many as potent as the classical bicyclic ß-amino carboxamide analogs, but with significant CYP1A2 inhibition. Overall, this exercise indicated that the ß-amino carboxamide moiety most likely facilitates an IMHB, and is essential for M4 PAM activity within classical bicyclic M4 PAM scaffolds.

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.

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 (Kp = 1.9, Kp,uu = 0.78), a feature devoid in all previously disclosed mGlu2 NAMs (Kps ≈ 0.3, Kp,uus ≈ 0.1). Moreover, this series, based on overall properties, represents an exciting lead series for potential mGlu2 PET tracer development.

Design and Synthesis of N-Aryl Phenoxyethoxy Pyridinones as Highly Selective and CNS Penetrant mGlu3 NAMs.

Herein, we detail the optimization of the mGlu3 NAM, VU0650786, via a reductionist approach to afford a novel, simplified mGlu3 NAM scaffold that engenders potent and selective mGlu3 inhibition (mGlu3 IC50 = 245 nM, mGlu2 IC50 > 30 µM) with excellent central nervous system penetration (rat brain/plasma Kp = 1.2, Kp,uu = 0.40). Moreover, this new chemotype, exemplified by VU6010572, requires only four synthetic steps and displays improved physiochemical properties and in vivo efficacy in a mouse tail suspension test (MED = 3 mg/kg i.p.).

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 and optimization of a novel series of highly CNS penetrant M4 PAMs based on a 5,6-dimethyl-4-(piperidin-1-yl)thieno[2,3-d]pyrimidine core.

This Letter describes the chemical optimization of a novel series of M4 positive allosteric modulators (PAMs) based on a 5,6-dimethyl-4-(piperidin-1-yl)thieno[2,3-d]pyrimidine core, identified from an MLPCN functional high-throughput screen. The HTS hit was potent and selective, but not CNS penetrant. Potency was maintained, while CNS penetration was improved (rat brain:plasma Kp=0.74), within the original core after several rounds of optimization; however, the thieno[2,3-d]pyrimidine core was subject to extensive oxidative metabolism. Ultimately, we identified a 6-fluoroquinazoline core replacement that afforded good M4 PAM potency, muscarinic receptor subtype selectivity and CNS penetration (rat brain:plasma Kp>10). Moreover, this campaign provided fundamentally distinct M4 PAM chemotypes, greatly expanding the available structural diversity for this exciting CNS target.