Homoisoflavonoids from Caesalpinia sappan displaying viral neuraminidases inhibition.

In this study, twelve neuraminidase (NA) inhibitory compounds 1-12 were isolated from heartwood of Caesalpinia sappan on the basis of their biological activities against three types of viral NAs. Of isolated homoisoflavonoids, sappanone A (2) showed the most potent NAs inhibitory activities with IC(50) values of 0.7 µM [H1N1], 1.1 µM [H3N2], and 1.0 µM [H9N2], respectively, whereas saturated homoisoflavonoid (3) did not show significantly inhibition. This result revealed that α,β-unsaturated carbonyl group in A-ring was the key requirements for viral NAs inhibitory activity. In our enzyme kinetic study, all NA inhibitors screened were found to be reversible noncompetitive types.