As part of a search for a new potassium channel opener, the 1, 4-benzoxazine skeleton derived from the benzopyran skeleton of cromakalim, was transformed into other fused rings such as 1, 4-benzothiazine, 1, 2, 3, 4-tetrahydroquinoline, 1, 2, 3, 4-tetrahydroquinoxaline, indoline, and 1, 5-benzoxazepine. The 1, 4-benzothiazine derivative displayed approximately 20 times more potent vasorelaxant activity than cromakalim.
