Synthetic studies on condensed-azole derivatives. I. Synthesis and anti- asthmatic activities of ω-substituted alkylthioimidazo[1,2-b]pyridazines
A series of novel ω-substituted alkylthioimidazo[1,2-b]pyridazines was designed and synthesized in an effort to find a novel anti-asthmatic agent. The anti-asthmatic activity of these compounds was evaluated on the basis of their ability to inhibit thromboxane A2 synthetase and platelet activating factor (PAF)-induced bronchoconstriction in guinea pigs. None of these compounds significantly inhibited thromboxane A2 synthetase, though, sulfonamide derivatives potently inhibited PAF-induced bronchoconstriction. Among them, 3-(imidazo[1,2-b]pyridazin-6-yl)thiopropanesulfonamide (5) showed the most potent inhibitory effect. The anti-asthmatic effects of compound 5 in experimental models were superior to those of theophylline.