Discovery of 2-Methyl-5-(1 H -pyrazol-4-yl)pyridines and Related Heterocycles as Promising M 4 mAChR Positive Allosteric Modulators for the Treatment of Neurocognitive Disorders.

The M 4 muscarinic acetylcholine receptor (mAChR) is a biological target for neurocognitive disorders. Compound 1 is an ago -PAM for the M 4 mAChR. Herein, we report the design, synthesis, and evaluation of novel putative M 4 mAChR PAMs based on 1 . These analogs were screened and then fully characterized in two functional assays (G oB protein activation and CAMYEL activation) to quantify their allosteric and ago -PAM properties against ACh. A selection of 7 M 4 PAMs were assessed for their ability to modulate ACh-mediated β-arrestin recruitment and revealed 4 distinct clusters of M 4 PAM activity: (1) analogs similar to 1 ( 24d ), (2) analogs demonstrating only allosteric agonism ( 23d ), (3) analogs with increased allosteric properties in CAMYEL activation ( 23b / 23f and 24a / 24b ), and (4) analogs with a biased modulatory effect toward β-arrestin recruitment ( 23i ). These novel M 4 chemical tools disclose discrete molecular determinants, allowing further interrogation of the therapeutic roles of cAMP and β-arrestin pathways in neurocognitive disorders.