This letter describes the synthesis and structure activity relationship (SAR) studies of structurally novel M antagonists, based on a 3-(4-aryl/heteroarylsulfonyl)piperazin-1-yl)-6-(piperidin-1-yl)pyridazine core, identified from a high-throughput screening campaign. A multi-dimensional optimization effort enhanced potency at human M (hM ICs<200nM), with only moderate species differences noted, and with enantioselective inhibition. Moreover, CNS penetration proved attractive for this series (rat brain:plasma K=2.1, K=1.1). Despite the absence of the prototypical mAChR antagonist basic or quaternary amine moiety, this series displayed pan-muscarinic antagonist activity across M (with 9- to 16-fold functional selectivity at best). This series further expands the chemical diversity of mAChR antagonists.
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