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

Although β 2 -agonists are crucial for treatment of chronic respiratory diseases, optimizing β 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 β 2 agonists featuring a 5-hydroxy-4 H -benzo[1,4]oxazin-3-one scaffold, which potently stimulated β 2 adrenoceptors (β 2 -ARs). Screening for the β 2 -agonistic activity and selectivity led to the identification of compound A19 (EC 50 = 3.7 pM), which functioned as a partial β 2 -agonist in HEK-293 cells containing endogenous β 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 β 2 agonist candidate for further study.