In contrast, the presence of saturated carbons of the C7 linker as in compounds 10–12might be responsible for the decreased activity compared to the others, e.g., compounds5, 9, and 13. Additionally, the methoxy substitution of C-3 in the aryl rings might increase the NA inhibitory properties, as observed in compounds 4, 5, and 13, compared to the structurally similar compounds 6, 7, and 8. In generally, inhibitory effects (IC50 values of these curcuminoids) on neuraminidase of avian influenza virus (H9N2) were similar to swine influenza (H1N1) (Table 2).