Synthesis and structure–activity relationships of 4,5-fused pyridazinones as histamine H3 receptor antagonists

Three series of novel 4,5-fused pyridazinones were synthesized as histamine H3 receptor antagonists. The 2,5,6,7-tetrahydrocyclopenta[d]pyridazin-1-one 5q and 5,6,7,8-tetrahydro-2H-phthalazin-1-one 5u displayed high affinity at both rat and human H3 receptors, and showed potent antagonist and full inverse agonist activity in functional assays.

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