Antiviral spirooliganones C and D with a unique spiro[bicyclo[2.2.2]octane-2,2′-bicyclo[3.1.0]hexane] carbon skeleton from the roots of Illicium oligandrum

Abstract

Two unprecedented polycyclic spirooliganones C and D (1 and 2) with a novel spiro[bicyclo[2.2.2]octane-2,2′-bicyclo[3.1.0]hexane] carbon skeleton, one known dimeric prenylated C₆C₃ compound (3), and a pair of new enantiomeric prenylated C₆C₃ compounds (+)-5 and (−)-5 together with their direct precursors (+)-4 and (−)-4 were isolated from the roots of Illicium oligandrum. Their structures and absolute configurations were elucidated by spectroscopic analysis, single crystal X-ray diffraction data, and electronic circular dichroism calculations. A possible biosynthetic pathway for compounds 1 and 2 involving the Diels-Alder reaction between (−)-sabinene and cyclic prenylated tetrahydropyrano-type C₆C₃ compounds was proposed. The characteristic prenylated C₆C₃ compounds (+)-4 and (−)-4 were separated on a chiral stationary phase and their absolute configurations were determined by calculated ECD for the first time. In the antiviral bioassays, compounds 1 and (+)-5 exhibited significant inhibitory activity against CVB3 with IC₅₀ values of 11.11 µmol/L and 1.11 µmol/L, respectively. Compounds 1 and 2 also showed moderate inhibition against influenza A (H1N1) virus.