Synthetic Studies on Condensed-Azole Derivatives. V. Synthesis and Anti-asthmatic Activities of ω-Sulfamoylalkyloxy[1, 2, 4]triazolo[1, 5-b]-pyridazines

A series of novel ([1, 2, 4]triazolo[1, 5-b]pyridazin-6-yl)oxyalkylsulfonamides was synthesized and evaluated for the ability to inhibit platelet activating factor (PAF)-induced bronchoconstriction in guinea pigs. The compounds bearing a gem-dialkyl or a cycloalkylidene group at the 2 position of the sulfamoylpropyloxy group in the side chain and a methyl group at the 7 position were found to have potent activity. Among them, 2, 2-diethyl-3-(7-methyl[1, 2, 4]-triazolo[1, 5-b]pyridazin-6-yl)oxypropanesulfonamide (13) showed excellent anti-asthmatic activity. Compounds 13 may be of significant value in the treatment of asthma and other respiratory diseases. The structure-activity relationships in this series of compounds are discussed.