SAR investigations of the 4- and 5-positions of a series of 4-amino-4H-pyran-2-carboxylic acid 6-carboxamides are reported. Potent inhibitors of influenza A sialidase with marked selectivity over the influenza B enzyme were obtained when the basic 4-amino substituent was replaced by hydroxyl or even deleted. Modifications at the 5-position exhibited a tight steric requirement, with trifluoroacetamide being optimal.
Wyatt, P. G., Coomber, B. A., Evans, D. N., Jack, T. I., Fulton, H. E., Wonacott, A. J., Colman, P., & Varghese, J. (2001). Sialidase inhibitors related to zanamivir. Further SAR studies of 4-amino-4H-pyran-2-carboxylic acid-6-propylamides. Bioorganic & Medicinal Chemistry Letters, 11(5), 669-673. https://doi.org/10.1016/S0960-894X(01)00019-1