Antiviral Spirooliganones A and B with Unprecedented Skeletons from the Roots of Illicium oligandrum

Two novel spirooliganones A (1) and (2), a pair of spiro carbon epimers, with a rare dioxaspiro skeleton were isolated from the roots of Illicium oligandrum. The structures were fully determined by spectroscopic analysis and chemical methods, especially modified Mosher’s method, and X-ray diffraction analysis. Spirooliganone B was found to exhibit more potent activities against coxsackie virus B3 and influenza virus A (H3N2) (IC₅₀ 3.70–5.05 μM) than spirooliganone A. The biosynthetic pathway involving a hetero-Diels–Alder reaction of the epimers was proposed.