This new M4 positive allosteric modulator (PAM) probe, ML293, is the result of an extended probe characterization project to improve in vivo PK properties and brain exposure. ML293 displayed modest potency at the human M4 receptor, EC50 = 1.3 μM, and excellent efficacy as noted by the leftward shift of the agonist concentration-response curve (14.6-fold). Importantly, ML293 displayed superior in vivo PK properties compared to the previous M4 probe molecules (ML108, ML173 and ML253) with low IV clearance (11.6 mL/min/kg) and excellent brain exposure (PO PBL, 10 mg/kg at 1 h, [Brain] = 10.3 μM, B:P = 0.85). Moreover, ML293 was selective for M4 (>30 μM versus, M1–3, M5), and possessed a clean ancillary pharmacological profile in a Ricerca radioligand binding panel of 68 G-protein-coupled receptors (GPCRs), ion channels and transporters with the exception of adenosine receptors. Here ML293 was found to be a potent ligand for antagonist of the A2A receptor; however the A2A antagonism will not confound in vivo evaluation of M4 PAM efficacy in schizophrenia models, whereas an A2A agonist could.