In order to exploit the 430-cavity in the active sites of neuraminidases, 22 zanamivir analogs with C-1 and C-4 modification were synthesized, and their inhibitory activities against both group-1 (H5N1, H1N1) and group-2 neuraminidases (H3N2) were determined. Compound 9f exerts the most potency, with IC(50) value of 0.013, 0.001, and 0.09 μM against H3N2, H5N1, and H1N1, which is similar to that of zanamivir (H3N2 IC(50) = 0.0014 μM, H5N1 IC(50) = 0.012 μM, H1N1 IC(50) = 0.001 μM). Pharmacokinetic studies of compound 9f in rats showed a much longer plasma half-life (t(1/2)) than that of zanamivir following administration (po dose). Molecular modeling provided information about the binding model between the new inhibitors and neuraminidase, with the elongated groups at the C-1-position being projected toward the 430-loop region. This study may represent a novel starting point for the future development of improved antiflu agents.