Development of tetrahydroquinazoline compounds as Fusion protein inhibitors for the treatment of respiratory syncytial virus.

Respiratory syncytial virus (RSV) is one of the leading causes of severe respiratory infections worldwide, particularly in pediatric and elderly populations. The RSV Fusion (F) protein, essential for viral entry and syncytium formation, represents a prime target for antiviral drug development. In this study, we constructed a compound class that contained saturated naphthene- and cyclic ether-fused pyrimidine bicyclic cores as potent Fusion inhibitors. Among these, the 5,6,7,8-tetrahydroquinazoline derivative 7d showed outstanding in vitro anti-RSV activity (RSV-long, EC50 = 3.65 ± 0.85 nM) and potent inhibition against multiple clinical isolates. Molecular docking, MD simulations, and MM-GBSA showed 7d tightly binds RSV pre-fusion F protein with strong affinity. 7d effectively inhibited RSV infection and syncytium formation in human nasal and airway organoids. The in vivo efficacy of 7d in reducing viral load and alleviating RSV-induced lung pathology was confirmed in both young and aged mouse models. By integrating in vitro, organoid, and in vivo models, this study validates compound 7d as a highly potent, lung-targeted RSV F protein inhibitor with promising therapeutic potential. These findings warrant further development of 7d as a novel antiviral candidate against RSV infection.