A functional high throughput screen identified a novel chemotype for the positive allosteric modulation (PAM) of the muscarinic acetylcholine receptor (mAChR) subtype 5 (M5). Application of rapid analog, iterative parallel synthesis efficiently optimized M5 potency to arrive at the most potent M5 PAMs prepared to date and provided tool compound 8n (ML380) demonstrating modest CNS penetration (human M5 EC50 = 190 nM, rat M5 EC50 = 610 nM, brain to plasma ratio (Kp) of 0.36).

This Letter describes the continued optimization of an MLPCN probe molecule (ML137) with a focused effort on the replacement/modification of the isatin moiety present in this highly selective M1 PAM. A diverse range of structures were validated as viable replacements for the isatin, many of which engendered sizeable improvements in their ability to enhance the potency and efficacy of acetylcholine when compared to ML137. Muscarinic receptor subtype selectivity for the M1 receptor was also maintained.

This Letter describes the further optimization of an MLPCN probe molecule (ML137) through the introduction of 5- and 6-membered spirocycles in place of the isatin ketone. Interestingly divergent structure–activity relationships, when compared to earlier M1 PAMs, are presented. These novel spirocycles possess improved efficacy relative to ML137, while also maintaining high selectivity for the human and rat muscarinic M1 receptor subtype.

This Letter describes the continued optimization of an MLPCN probe molecule (ML012) through an iterative parallel synthesis approach. After exploring extensive modifications throughout the parent structure, we arrived at a more highly M1-selective antagonist, compound 13l (VU0415248). Muscarinic subtype selectivity across all five human and rat receptors for 13l, along with rat selectivity for the lead compound (ML012), is presented.

This Letter describes the continued optimization of the MLPCN probe molecule ML071. After introducing numerous cyclic constraints and novel substitutions throughout the parent structure, we produced a number of more highly potent agonists of the M1 mACh receptor. While many novel agonists demonstrated a promising ability to increase soluble APPα release, further characterization indicated they may be functioning as bitopic agonists. These results and the implications of a bitopic mode of action are presented.

This Letter describes a chemical lead optimization campaign directed at VU0108370, a weak M1 PAM hit with a novel chemical scaffold from a functional HTS screen within the MLPCN. An iterative parallel synthesis approach rapidly established SAR for this series and afforded VU0405652 (ML169), a potent, selective and brain penetrant M1 PAM with an in vitro profile comparable to the prototypical M1 PAM, BQCA, but with an improved brain to plasma ratio.This Letter describes a chemical lead optimization campaign directed at VU0108370, a weak M1 PAM hit with a novel chemical scaffold from a functional HTS screen within the MLPCN. An iterative parallel synthesis approach rapidly established SAR for this series and afforded VU0405652 (ML169), a potent, selective and brain penetrant M1 PAM with an in vitro profile comparable to the prototypical M1 PAM, BQCA, but with an improved brain to plasma ratio.