A series of 3-alkylamino-4H-pyrido[2,3-e]-1,2,4-thiadiazine 1, 1-dioxides structurally related to diazoxide and pinacidil were synthesized and tested as possible K(ATP) channel openers on isolated pancreatic endocrine tissue as well as on isolated vascular, intestinal, and uterine smooth muscle. In contrast to previously described 3-alkylamino-4H-pyrido[4,3-e]-1,2,4-thiadiazine 1, 1-dioxides, most of the new compounds were found to be poorly active on B-cells but exhibited clear vasorelaxant properties. 3-(3, 3-Dimethyl-2-butylamino)-4H-pyrido[2,3-e]-1,2,4-thiadiazine 1, 1-dioxide (4d) and 7-chloro-3-(3, 3-dimethyl-2-butylamino)-4H-pyrido[2,3-e]-1,2,4-thiadiazine 1, 1-dioxide (5d), two compounds bearing the alkyl side chain of pinacidil, were found to be the most active representatives of their respective series on rat aorta rings. 3-Cycloalkylalkylamino- and 3-aralkylamino-7-chloro-4H-pyrido[2,3-e]-1,2,4-thiadiazine 1, 1-dioxides also expressed myorelaxant activity on electrically stimulated guinea pig ileum and on oxytocin-induced contractions of the rat uterus. Further biological investigations ((86)Rb efflux measurements, vasodilator potency on 30 and 80 mM KCl-induced contractions in the absence and presence of glibenclamide) revealed that compounds 4d and 5d, but not compound 5f, expressed the pharmacological profile of classical K(ATP) channel openers. In conclusion, by changing the position of the nitrogen atom in the pyridine ring, we now have obtained a family of drugs expressing an opposite tissue selectivity. Taken as a whole, the present findings also suggest that 3-alkylamino-4H-pyrido[2,3-e]-1,2,4-thiadiazine 1, 1-dioxides such as 4c, 4d, 5c, and 5d may be considered as new examples of K(ATP) channel openers expressing a pharmacological profile similar to that of pinacidil and diazoxide.

4-N-Substituted and -unsubstituted 3-alkyl- and 3-(alkylamino)-4H-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxides were synthesized and tested vs diazoxide and selected 3-alykl- and 3-(alkylamino)-7-chloro-4H-1,2,4-benzothiadiazine 1,1-dioxides as potassium channel openers on pancreatic and vascular tissues. Several 4-N-unsubstituted 3-(alkylamino)pyridothiadiazines and some 3-(alkylamino)-7-chlorobenzothiadiazines were found to be more potent than diazoxide for the inhibition of the insulin-releasing process. Moreover, the 3-(alkylamino)pyridothiadiazines appeared to be more selective for the pancreatic than for the vascular tissue. By means of the pharmacological results obtained on pancreatic B-cells, structure--activity relationships were deduced and a pharmacophoric model for the interaction of these drugs with their receptor site associated to the pancreatic K(ATP) channel was proposed. According to their selectivity for the B-cell (endocrine tissue) vs the vascular (smooth muscle tissue) ionic channel, selected 3-(alkylamino)-4H-pyrido[4,3-e]-1,2,4,-thiadiazine 1,1-dioxides may serve as pharmacological tools in studying the K(ATP) channels ("pancreatic-like" K(ATP) channels) in other tissues.

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