We report here the exploitation of the 150-cavity in the active sites of group-1 neuraminidases for the design of new triazole-containing carbocycles related to oseltamivir. Inhibition studies with virus-like particles (VLPs) containing the influenza virus neuraminidase-1 (N1) activity indicate that several candidates are inhibitors, with K(i) values in the 10(-5)-10(-8) M range. In contrast, a known candidate that preserves the free amino group and a new candidate containing a guanidine function are better inhibitors, with K(i) values of 1.5 × 10(-9) and 4.6 × 10(-10) M, respectively. The most active inhibitor of the N1 enzyme in the triazole series was selective for the N1 class and showed significantly less inhibition (K(i) = 2.6 μM vs 0.07 μM) of the free influenza virus neuraminidase-2 (N2). In addition, saturation transfer difference (STD) NMR spectroscopic studies with this compound and the VLPs show that the entire molecule forms contacts with residues in the active site. These data taken together support our proposed binding mode in which the active site and the adjoining 150-cavity are both occupied.