Oseltamivir carboxylate, the active metabolite of oseltamivir, was obtained from Charnwood Molecular (Loughborough, U.K.) through synthesis via the NBoc-protected acid from oseltamivir phosphate. Amantadine was obtained from Moehs Catalana (Barcelona, Spain). Ribavirin and rimantadine were purchased from Sigma-Aldrich (St. Louis, MO). Peramivir was obtained from Jubilant Chemsys LTD (Uttar Pradesh, India) as free base through NBoc synthesis, and purity was confirmed using NMR and chiral HPLC. Zanamivir was obtained from Haorui Pharma-Chem, Inc. (Edison, NJ). 