N -[(Thiophen-3-yl)methyl]benzamides as Influenza Virus Fusion Inhibitors Acting on H1 and H5 Hemagglutinins

Novel antiviral drugs are needed to prepare against infections from influenza A virus (IAV). Here a series of N -[(thiophen-3-yl)methylbenzamides which target the hemagglutinin (HA)-mediated fusion process is reported. The most active compound, VF-57a , displays a 50% effective concentration (EC ₅₀ ) of ∼0.8 μM and antiviral selectivity index >130, in Madin-Darby canine kidney (MDCK) cells infected with A/H1N1 virus. VF-57a proved to be a strong inhibitor of A/H1N1- and A/H5N1-pseudovirus entry (EC ₅₀ values of 0.3 and 0.8 µM, respectively). Cell-cell fusion assays in HA-expressing cells, surface plasmon resonance-based assessment of HA protein refolding, and resistance studies suggested that VF-57a prevents the conformational change of HA at acidic pH. Molecular modelling highlighted the role of the dimethylthiophene moiety and the amide-based tether in the anchoring to the binding cavity of HA. Our findings support further development of this class of IAV fusion inhibitors against A/H1N1 and A/H5N1 viruses.