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

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 C_(6)single bondC_(3)compound(3),and a pair of new enantiomeric prenylated C_(6)single bondC_(3)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 C_(6)single bondC_(3)compounds was proposed.The characteristic prenylated C_(6)single bondC_(3)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 IC_(50)values of 11.11μmol/L and 1.11μmol/L,respectively.Compounds 1 and 2 also showed moderate inhibition against influenza A(H1N1)virus.