The discovery of VU0486846: steep SAR from a series of M1 PAMs based on a novel benzomorpholine core

This letter describes the chemical optimization of a new series of M1 positive allosteric modulators (PAMs) based on a novel benzomorpholine core, developed via iterative parallel synthesis, and culminating in the highly utilized rodent in vivo tool compound, VU0486846 (7), devoid of adverse effect liability. This is the first report of the optimization campaign (SAR and DMPK profiling) that led to the discovery of VU0486846 and details all of the challenges faced in allosteric modulator programs (both steep and flat SAR, as well as subtle structural changes affecting CNS penetration and overall physiochemical and DMPK properties).

Effects of muscarinic receptor antagonists on cocaine discrimination in wild-type mice and in muscarinic receptor M1, M2, and M4 receptor knockout mice

Muscarinic M₁/M₄ receptor stimulation can reduce abuse-related effects of cocaine and may represent avenues for treating cocaine addiction. Muscarinic antagonists can mimic and enhance effects of cocaine, including discriminative stimulus (S^D) effects, but the receptor subtypes mediating those effects are not known. A better understanding of the complex cocaine/muscarinic interactions is needed to evaluate and develop potential muscarinic-based medications. Here, knockout mice lacking M₁, M₂, or M₄ receptors (M₁^-/-, M₂^-/-, M₄^-/-), as well as control wild-type mice and outbred Swiss-Webster mice, were trained to discriminate 10mg/kg cocaine from saline. Muscarinic receptor antagonists with no subtype selectivity (scopolamine), or preferential affinity at the M₁, M₂, or M₄ subtype (telenzepine, trihexyphenidyl; methoctramine, AQ-RA 741; tropicamide) were tested alone and in combination with cocaine. In intact animals, antagonists with high affinity at M₁/M₄ receptors partially substituted for cocaine and increased the S^D effect of cocaine, while M₂-preferring antagonists did not substitute, and reduced the S^D effect of cocaine. The cocaine-like effects of scopolamine were absent in M₁^-/- mice. The cocaine S^D attenuating effects of methoctramine were absent in M₂^-/- mice and almost absent in M₁^-/- mice. The findings indicate that the cocaine-like S^D effects of muscarinic antagonists are primarily mediated through M₁ receptors, with a minor contribution of M₄ receptors. The data also support our previous findings that stimulation of M₁ receptors and M₄ receptors can each attenuate the S^D effect of cocaine, and show that this can also be achieved by blocking M₂ autoreceptors, likely via increased acetylcholine release.

Further optimization of the M1 PAM VU0453595: Discovery of novel heterobicyclic core motifs with improved CNS penetration

This Letter describes the continued chemical optimization of the VU0453595 series of M1 positive allosteric modulators (PAMs). By surveying alternative 5,6- and 6,6-heterobicylic cores for the 6,7-dihydro-5H-pyrrolo[3,4-b]pyridine-5-one core of VU453595, we found new cores that engendered not only comparable or improved M1 PAM potency, but significantly improved CNS distribution (Kps 0.3-3.1). Moreover, this campaign provided fundamentally distinct M1 PAM chemotypes, greatly expanding the available structural diversity for this valuable CNS target, devoid of hydrogen-bond donors.

Discovery and SAR of muscarinic receptor subtype 1 (M1) allosteric activators from a molecular libraries high throughput screen. Part 1: 2,5-dibenzyl-2H-pyrazolo[4,3-c]quinolin-3(5H)-ones as positive allosteric modulators

Results from a 2012 high-throughput screen of the NIH Molecular Libraries Small Molecule Repository (MLSMR) against the human muscarinic receptor subtype 1 (M1) for positive allosteric modulators is reported. A content-rich screen utilizing an intracellular calcium mobilization triple-addition protocol allowed for assessment of all three modes of pharmacology at M1, including agonist, positive allosteric modulator, and antagonist activities in a single screening platform. We disclose a dibenzyl-2H-pyrazolo[4,3-c]quinolin-3(5H)-one hit (DBPQ, CID 915409) and examine N-benzyl pharmacophore/SAR relationships versus previously reported quinolin-3(5H)-ones and isatins, including ML137. SAR and consideration of recently reported crystal structures, homology modeling, and structure-function relationships using point mutations suggests a shared binding mode orientation at the putative common allosteric binding site directed by the pendant N-benzyl substructure.

Identification of a methoxynaphthalene scaffold as a core replacement in quinolizidinone amide M(1) positive allosteric modulators

A series of methoxynaphthalene amides were prepared and evaluated as alternatives to quinolizidinone amide M1 positive allosteric modulators. A methoxy group was optimal for M1 activity and addressed key P-gp issues present in the aforementioned quinolizidinone amide series.