3- and 4-Substituted 4H-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxides as potassium channel openers: Synthesis, pharmacological evaluation, and structure-activity relationships

4-N-Subsituted 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-alkyl- 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.