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

Novel antiviral drugs are needed to prepare for infections from influenza A virus (IAV). Here, a series of N-[(thiophen-3-yl)methyl]benzamides, which target the hemagglutinin (HA)-mediated fusion process, is reported. The most active compound, VF-57a, displays a 50% effective concentration (EC₅₀) of ∼0.8 μM and an 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 (EC₅₀ 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 modeling highlighted the role of the dimethylthiophene moiety and the amide-based tether in anchoring to the binding cavity of HA. Our findings support the further development of this class of IAV fusion inhibitors against A/H1N1 and A/H5N1 viruses.