The design and synthesis of a novel class of 1,4-benzothiazines targeted for the large-conductance calcium-activated potassium channels (BK) are presented. In vitro functional characterization of BK channel opening activity was assessed by measuring the relaxation of isolated rat aortic rings precontracted with KCl 20 mM. The results of this study show that the 1,4-benzothiazine heterocyclic nucleus is a suitable backbone for designing novel BK-openers; indeed, some of these new 1,4-benzothiazine derivatives had a vasorelaxant potency comparable or superior to that of reference BK-activator NS-1619 (1).