Discovery and Identification of Novel 5-Hydroxy-4H-benzo[1,4]oxazin-3-one Derivatives as Potent ₂-Adrenoceptor Agonists through Structure-Based Design, Synthesis, and Biological Evaluation

Although beta(2)-agonists are crucial for treatment of chronic respiratory diseases, optimizing beta(2)-agonistic activity and selectivity remains essential for achieving favorable therapeutic outcomes. A structure-based molecular design workflow was employed to discover a novel class of beta(2) agonists featuring a 5-hydroxy-4H-benzo[1,4]oxazin-3-one scaffold, which potently stimulated beta(2) adrenoceptors (beta(2)-ARs). Screening for the beta(2)-agonistic activity and selectivity led to the identification of compound A19 (EC50 = 3.7 pM), which functioned as a partial beta(2)-agonist in HEK-293 cells containing endogenous beta(2)-ARs. Compound A19 exhibited significant relaxant effects, rapid onset time (Ot(50) = 2.14 min), and long duration of action (>12 h) on isolated guinea pig tracheal strips, as well as advantageous pharmacokinetic characteristics in vivo, rendering A19 suitable for inhalation administration. Moreover, A19 suppressed the upregulation of inflammatory cytokines and leukocytes and improved lung function in a rat model of COPD, thereby indicating that A19 is a potential beta(2) agonist candidate for further study.