Furin-IN-3 (Compound 9) is a potent and selective inhibitor of the proprotein convertase furin enzyme, with a Ki value of 12.4 nM. It has a Ki value of 278 nM for PC7. Furin-IN-3 demonstrates significant antiviral activity against the influenza A virus (H7N7 strain SC35M) which relies on furin. It inhibits the cleavage and activation of viral hemagglutinin (HA), preventing the fusion of the viral membrane with the host cell membrane, thereby inhibiting viral replication and proliferation. Furin-IN-3 is useful for studying infections, such as influenza virus infection.