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[4.3.1.1(5,7)]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.