Pyridazinones. 3. Synthesis, antisecretory, and antiulcer activities of 2-cyanoguanidine derivatives.

3(2H)-Pyridazinone derivatives having a 2-cyanoguanidine moiety, as well as a sulfur or an oxygen atom in the alkylene side chain, were synthesized and evaluated for gastric antisecretory and antiulcer activities. The key intermediates, free amines having a thioether linkage, were synthesized by the reaction of 2-(omega-chloroalkyl) derivatives with cysteamine, while other intermediates having an ether linkage were synthesized from 2-(omega-chloroalkyl)oxymethyl derivatives. These free amines were converted via the 3-cyano-2-methyl-1-isothiourea derivatives into the desired 2-cyano-3-substituted-1-guanidine derivatives. All compounds synthesized were evaluated for gastric antisecretory activity in the pylorus-ligated rat by the method of Shay, and selected compounds were evaluated in the stress-induced ulcer test in rat. Structure-activity relationships are discussed. The molecular features for the best activities are a phenyl group in the C-6 position of the 3(2H)-pyridazinone ring, a four-atom chain length between the 3(2H)-pyridazinone ring and the 2-cyanoguanidine moiety, and a thioether rather than an ether linkage. Among them, compound 14, 2-[[[2-(2-cyano-3-methyl-1-guanidino)ethyl]thio]methyl]-6-phenyl-3 (2H)-pyridazinone, had the most potent antisecretory and antiulcer activities. These compounds are neither histamine H2 receptor inhibitors nor anticholinergic agents.