Norwilsonnol A, an immunosuppressive polycyclic polyprenylated acylphloroglucinol with a spiro[5-oxatricyclo[6.4.0.03,7]dodecane-6′,1-1′,2′-dioxane] system from Hypericum wilsonii

Norwilsonnol A (1), a structurally complex polycyclic polyprenylated acylphloroglucinol (PPAP) bearing an unprecedented scaffold, together with a new biosynthetic analogue, norwilsonnol B (2), was isolated from Hypericum wilsonii. Their structures were confirmed by spectroscopic analyses, electronic circular dichroism (ECD) calculations and X-ray crystallographic data. Compound 1 was characterized by a new 6/6/5/5 tetracyclic system based on a spiro[5-oxatricyclo[6.4.0.0(3,7)]dodecane-6 ',1-1 ',2 '-dioxane] core. More importantly, 1 displayed remarkable immunosuppressive activities in murine splenocytes and human T cells stimulated by anti-CD3/anti-CD28 monoclonal antibodies (mAbs).