Discovery of Diphenyl Ether Derivatives as Novel BK_Ca Channel Activators: Structure-Activity Relationship, Cryo-EM Complex Structures, and In Vivo Animal Studies

The BK_Ca channel, a large-conductance calcium-activated potassium channel, plays a crucial role in maintaining the homeostasis of the micturition cycle and airway-related functions. In this study, we optimized a novel BK_Ca channel activator, 4d, with a diphenyl ether structure identified from library screening. This led to the discovery of potent activators, 10b (EC₅₀ = 0.12 μM, cell-based assay) and 51b, an orally bioavailable derivative. Compound 10b demonstrated potent in vivo efficacy in a spontaneous hypertensive rat (SHR) of urinary incontinence model, while compound 51b showed dose-dependent cough suppression efficacy with an ED₅₀ of 11.8 mg/kg in a citric acid-induced cough model. Furthermore, we reported the cryo-electron microscopy (cryo-EM) structures of the BK_Ca channel in complex with 10b and 51b at resolutions of 2.8 and 3.4 Å. Based on structural analyses, we determined the binding sites and key interaction residues of 51b, which were validated via mutation studies.