ent-Kaurane diterpenoids from Isodon henryi and their anti-inflammatory activities

Phytochemical investigation of the 70% ethanol extract of Isodon henryi Kudô afforded fifteen ent-kaurane diterpenoids, including nine previously undescribed compounds, named isohenolides C–K (1–9). Compounds 1–6 featured an unusual 6,7;8,15-diseco-7,20-olide ent-kaurane diterpenoid scaffold, in which 1 also possessed an 11,15-lactone ring while 2–6 all contained a free α-methylene-γ-carboxylic acid. Compound 6 was also a rare 6,8-cyclo-7,20-olide ent-kauranoid. Their structures were elucidated primarily by HRESIMS, 1D and 2D NMR spectroscopy, electronic circular dichroism and X-ray diffraction (Cu Kα) methods. Additionally, most compounds were also screened for anti-inflammatory actions against lipopolysaccharide-induced RAW 264.7 cells, and compounds 9 and 13 exhibited stronger nitric oxide inhibition, with IC₅₀ values of 15.99 ± 0.75 and 18.19 ± 0.42 μM, respectively.