Dioxasampsones A and B, Two Polycyclic Polyprenylated Acylphloroglucinols with Unusual Epoxy-Ring-Fused Skeleton from Hypericum sampsonii

Dioxasampsones A and B (1 and 2), two
new polycyclic polyprenylated acylphloroglucinols with an unusual
epoxy-ring-fused skeleton by new ways of cyclization, along with a
new nor-PPAPs hypersampson R (3) with the loss of C-31–33
in isopentenyl, were isolated from the aerial parts of Hypericum sampsonii. 1 possessed an
unexpected hexacyclic skeleton with a rare 2,7-dioxabicyclo[2.2.1]­heptane
moiety, and 2 featured a unique tetrahydrofuro­[3,4-b]­furan-fused tricycle­[4.3.1.15,7]­undecane skeleton.
The gross structures of the new compounds were determined by extensive
NMR spectroscopic methods. Their absolute configurations were deduced
by single-crystal X-ray diffraction and ECD calculations.