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]hexanel carbon skeleton, one known dimeric prenylated C-6-C-3 compound (3), and a pair of new enantiomeric prenylated C-6-C-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-C-3 compounds was proposed. The characteristic prenylated C-6-C-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 IC50 values of 11.11 mu mol/L and 1.11 mu mol/L, respectively. Compounds 1 and 2 also showed moderate inhibition against influenza A (H1N1) virus. (C) 2022 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.