Novel potassium channel activators : Synthesis and structure-activity relationship studies of 3,4-dihydro-2H-1,4-benzoxazine derivatives

Strong potassium channel-activating effects were found among a series of novel 4-substituted 3, 4-dihydro-2H-1, 4-benzoxazine derivatives. The key step in preparation was the nucleophilic substitution of 3, 4-dihydro-2H-1, 4-benzoxazine (3) with activated halogenopyridines, such as halogenopyridine N-oxides (15a-c) and the borane adduct (15d) of 4-bromopyridine. Structure-activity relationship studies identified 2-(3, 4-dihydro-2, 2-dimethyl-6-nitro-2H-1, 4-benzoxazin-4-yl)pyridine-1-oxide (16a : YM934) as the optimal compound. This compound (16a) showed a more potent oral antihypertensive effect than cromakalim in conscious spontaneously hypertensive rats.