All compounds were displayed as noncompetitive inhibitors because increasing of the substrate concentrations resulted in a family of lines that intersected at a non-zero point on the x axis (−Ki) ( Fig. 4A–D). A summary of the Ki values for the tested compounds was concurred with IC50 values ( Table 2 and Fig. 4E–H). These results are somewhat congruent with those of reported results for antiviral activity of other diarylheptanoids ( Grienke et al., 2010 and Tung et al., 2010) as well as a recent report indicating that curcumin might be beneficial for the treatment of an influenza virus infection by inhibiting haemagglutinin (HA) protein ( Chen et al., 2010).