Formohyperins G–L, polycyclic prenylated benzoylphloroglucinols from the flowers of Hypericum formosanum

Phytochemical study on the flowers of Hypericum formosanum Maxim. (Hypericaceae) led to the isolation of formohyperins G–L (1–6), whose structures were assigned by detailed spectroscopic analysis. Formohyperins G–L (1–6) are new benzoylphloroglucinols substituted by a C₁₀ unit, a prenyl group, and a methyl group. Formohyperins G–J (1–4) possess a 6/6/6-tricyclic structure, while formohyperins K (5) and L (6) have a unique 6/6/5/4-tetracyclic structure consisting of cyclohexadienone, dihydropyrane, cyclopentane, and cyclobutane rings. The absolute configurations of 1–6 were deduced by analysis of the ECD spectra. Formohyperins G–J (1–4) and L (6) were found to show potent inhibitory activities against IL-1β release from LPS-treated murine microglial cells with EC₅₀ values of 5.0, 10.9, 6.3, 10.8, and 13.7 µM, respectively, without cytotoxicity. 6-O-Methylformohyperins G (1a) and I (3a) also exhibited the inhibitory activities with EC₅₀ values of 4.7 and 2.7 µM, respectively, although they were cytotoxic against microglial cells.

Graphical abstract