MBX2546 is an Influenza A Virus Fusion Inhibitor. MBX2546 binds to HA and inhibits HA-mediated membrane fusion. Both binding and stabilization of HA by MBX2546 are required for the inhibition of viral infection. Mutations in MBX2546-resistant influenza A/PR/8/34 (H1N1) viruses are mapped in the HA stem region near the amino terminus of HA2.