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This letter describes progress towards an M 4 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(6 H)-one core. Medicinal chemistry design efforts yielded two novel tricyclic cores that enhanced M 4 PAM potency, regained CNS penetration, displayed favorable DMPK properties and afforded robust in vivo efficacy in reversing amphetamine-induced hyperlocomotion in rats. [ABSTRACT FROM AUTHOR]

• First disclosure of VU6005806/AZN-00016130, an M 4 PAM profiled as a putative candidate. • Novel SAR findings based on novel variations to the C3 position on the pyridazine core. • Minimum effective dose of 0.56 mg/kg po in rat AHL. This letter describes progress towards an M 4 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 M 4 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 β-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. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • First description of the role of the β-aminocarboxamide moiety within M 4 PAM scaffolds. • Novel des -amino and tricyclic variant M 4 PAMs. • The role of the IMHB motif was established, and could be re-enforced by tricycles. Abstract This letter describes a focused exercise to explore the role of the β-amino carboxamide moiety found in all of the first generation M 4 PAMs and question if the NH 2 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 β-amino carboxamide that engendered P-gp and contributed to solubility liabilities), we removed the NH 2 , generating des -amino congeners and surveyed other functional groups in the β-position. These modifications led to weak M 4 PAMs with poor DMPK properties. Cyclization of the β-amino carboxamide moiety by virtue of a pyrazole ring re-enforced the IMHB, led to potent (and patented) M 4 PAMs, many as potent as the classical bicyclic β-amino carboxamide analogs, but with significant CYP1A2 inhibition. Overall, this exercise indicated that the β-amino carboxamide moiety most likely facilitates an IMHB, and is essential for M 4 PAM activity within classical bicyclic M 4 PAM scaffolds. [ABSTRACT FROM AUTHOR]

This Letter details the discovery and subsequent optimization of a novel M 4 PAM scaffold based on an 6-fluoro-4-(piperidin-1-yl)quinoline-3-carbonitrile core, which represents a distinct departure from the classical M 4 PAM chemotypes. Optimized compounds in this series demonstrated improved M 4 PAM potency on both human and rat M 4 (4 to 5-fold relative to HTS hit), and displayed attractive physicochemical and DMPK profiles, including good CNS penetration (rat brain:plasma K p = 5.3, K p,uu = 2.4; MDCK-MDR1 (P-gp) ER = 1.1). [ABSTRACT FROM AUTHOR]

This letter describes the chemical optimization of a novel series of M 4 positive allosteric modulators (PAMs) based on a 5-amino-thieno[2,3- c ]pyridazine core, developed via iterative parallel synthesis, and culminating in the highly utilized rodent in vivo tool compound, VU0467154 ( 5 ). This is the first report of the optimization campaign (SAR and DMPK profiling) that led to the discovery of VU0467154, and details all of the challenges faced in allosteric modulator programs (steep SAR, species differences in PAM pharmacology and subtle structural changes affecting CNS penetration). [ABSTRACT FROM AUTHOR]

This Letter details our efforts to replace the 3-amino moiety, an essential pharmacophore for M 4 PAM activity in most M 4 PAMs to date, within the thieno[2,3- b ]pyridine core, as the β-amino carboxamide motif has been shown to engender poor solubility, varying degrees of P-gp efflux and represents a structural alert. A scaffold hopping exercise identified a novel 2,4-dimethylquinoline carboxamide core that provided M 4 PAM activity and good CNS penetration without an amino moiety. In addition, MacMillan photoredox catalysis chemistry was essential for construction of the 2,4-dimethylquinoline core. [ABSTRACT FROM AUTHOR]