. The virus stock was titrated using the NA activity assay, and the optimal virus dilution (1:64 dilution) for the neuraminidase inhibition assay was selected. Compounds were tested for NA inhibitory activity at 100 μM. Fluorescence was measured by an ELISA Reader (Molecular Devices; Lmax II384) at an emission of 460 nm and excitation of 360 nm. A zanamivir control (0.02 μM, MedChemExpress, Monmouth Junction, NJ, USA) was included for comparison.