Synthetic Studies on Condensed-Azole Derivatives. III. Synthesis and Anti-asthmatic Activities of C-Substituted Alkyl Side Chain Derivatives of ω-Sulfamoylalkylthioimidazo[1, 2-b]pyridazines and Related Compounds

A series of novel alkylthioimidazo[1, 2-b]pyridazines was synthesized and evaluated for ability to inhibit platelet activating factor (PAF)-induced bronchoconstriction in guinea pigs. Among them, 3-(imidazo[1, 2-b]pyridazin-6-yl)thio-2, 2-dimethylpropanesulfonamide (15) showed the most potent inhibitory effect. The structure-activity relationships in this series of compounds, in particular, the effects of conversiton of the imidazopyridazine ring into other heterocyclic rings, introduction of a substituent group at the 2 or 3 position of the imidazopyridazine ring and introduction of a substituent group into the alkyl side chain, are also discussed.