BCX-1898, a cyclopentane derivative, is an orally active and selective influenza virus neuraminidase inhibitor. BCX-1898 has antiviral activity with EC 50 s of <0.01-21 μM on influenza A (H1N1, H3N2, and H5N1) and influenza B viruses replication in MDCK cells. BCX-1898 shows protection against the mouse influenza model.