Norascyronones A and B, 2,3,4-nor-Polycyclic Polyprenylated Acylphloroglucinols from Hypericum ascyron

Phytochemical study of Hypericum ascyron led to the characterization of norascyronones A–C (1–3), metabolites derived from bicyclic polyprenylated acylphloroglucinols by losing eight carbons (C-2/3/4 of core and the isoprenyl at C-3). Compounds 1/2 with an unprecedented 6/6/5/6 ring system should be generated via [4 + 2] intramolecular cyclization of 3. Their structures were determined by spectroscopic and X-ray diffraction data. Compounds 1 and 2 showed cytotoxicities against the SK-BR-3 cell line (IC50 4.3 and 7.8 μM).