Antiviral Spirotriscoumarins A and B: Two Pairs of Oligomeric Coumarin Enantiomers with a Spirodienone-Sesquiterpene Skeleton from Toddalia asiatica.

Two pairs of oligomeric coumarin enantiomers, spirotriscoumarin A [(+)-1 and (-)-1] and spirotriscoumarin B [(+)-2 and (-)-2], with a spirodienone-sesquiterpene fused skeleton were isolated from Toddalia asiatica. Their structures were unambiguously established using spectroscopic data, X-ray diffraction analysis, and the electronic circular dichroism (ECD) method. The racemic mixtures (±)-1 and (±)-2 exhibit 3-to-6-fold stronger antiviral activity against influenza virus A (H3N2) (IC50: 3.13 and 2.87 μM, respectively) than their corresponding optically pure enantiomers.