Bioisosteric replacement and related analogs in the design, synthesis and evaluation of ligands for muscarinic acetylcholine receptors

Previous structure-activity relationship studies involving a series of lactone-based muscarinic ligands identified a lead compound containing a diphenylmethylpiperazine moiety (4; IC₅₀ = 340 nM). The purpose of the present work is to investigate 1,3-benzodioxoles, 4,4-diethyl substituted tetrahydrofurans, 5-substituted oxazolidinones and chromones as bioisosteric replacements for the lactone ring in a novel series of muscarinic ligands. The approach provided compounds with improved % inhibition values and identified a non-selective muscarinic ligand with an IC₅₀ value of 280 nM. The structure-activity relationship for this new series will be discussed. Selected compounds were evaluated in preliminary assays for subtype selectivity and were found to be non-selective.