Anti-inflammatory labdane diterpenoids from Leonurus japonicus Houtt.

Seven undescribed labdane diterpenoids, japonicones A-G, were isolated from the aerial parts of Leonurus japonicus Houtt. Japonicones C-G contained two keto carbonyl groups in their structures attached to C-3 and C-7, which are rare for labdane diterpenoids. The structures and absolute configurations of japonicones A-G were established by means of spectroscopic analyses (HRESIMS, 1D and 2D NMR, and ECD). Their anti-inflammatory activities were evaluated by measuring their inhibitory effects on PGE₂ production in LPS-stimulated RAW264.7 macrophages. Japonicones A-D and G showed inhibition of PGE₂ production with IC₅₀ values in the range of 8.62-30.71 μM (the positive control paracetamol showed an IC₅₀ = 5.79 μM).