Among anti-influenza viral drug candidates, guanidinooseltamivircarboxylate (GOC) has been identified to be highly potentagainst wild-type and OS-resistant virus strains.1,5,14−16 The presenceof the guanidine group provides additional interactions with the E226residue in NA, resulting in a stronger binding affinity of GOC with the H275Y mutant NA when compared to OSC. Here, XK is linked to influenza.