Spirocyclic replacements for the isatin in the highly selective, muscarinic M1 PAM ML137: The continued optimization of an MLPCN probe molecule

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 M-1 PAMs, are presented. These novel spirocycles possess improved efficacy relative to ML137, while also maintaining high selectivity for the human and rat muscarinic M-1 receptor subtype. (C) 2013 Elsevier Ltd. All rights reserved.