Discovery, Synthesis and Characterization of a Highly Muscarinic Acetylcholine Receptor (mAChR)-Selective M5-Orthosteric Antagonist, VU0488130 (ML381): A Novel Molecular Probe

Of the five G-protein-coupled muscarinic acetylcholine receptors (mAChRs; M-1-M-5), M-5 is the least explored and understood due to a lack of mAChR subtype-selective ligands. We recently performed a high-throughput functional screen and identified a number of weak antagonist hits that are selective for the M-5 receptor. Here, we report an iterative parallel synthesis and detailed molecular pharmacologic profiling effort that led to the discovery of the first highly selective, central nervous system (CNS)-penetrant M-5-orthosteric antagonist, with sub-micromolar potency (hM(5) IC50=450 nm, hM(5) K-i=340 nm, M-1-M-4 IC50 > 30 mu m), enantiospecific inhibition, and an acceptable drug metabolism and pharmacokinetics (DMPK) profile for in vitro and electrophysiology studies. This compound will be a powerful tool and molecular probe for the further investigation into the role of M-5 in addiction and other diseases.