Purity >98%. Respiratory syncytial virus (RSV) is the leading cause of respiratory tract infections in humans. RSV F protein, which mediates fusion of the viral envelope with the host cell membrane, has become a target of anti-RSV treatment. VP-14637 is a small molecule inhibitor of RSV that demonstrates antiviral activity with an EC50 value of 1.4 nM. It interferes directly with RSV fusion (EC50 = 5.4 nM), binding to the viral F protein, which allows simultaneous interaction with both of the heptad repeat domains of the F protein trimer.