Halimane and labdane diterpenoids from Leonurus japonicus and their anti-inflammatory activity.

Ten highly oxygenated diterpenoids (nine undescribed ones) were isolated from the aerial parts of Leonurus japonicus Houtt. 14,15-Dinor-labd-5,8-dien-3,13-dione was a 14,15-dinor-labdane diterpenoid possessing a C₁₈ skeleton. 7β,9α-Dihydroxy-6-oxo-labd-13-en-15,16-amide represented a rare example of labdane diterpenoid featuring an α,β-unsaturated-γ-lactam moiety. The structures of all compounds were elucidated using spectroscopic data analyses and comparisons. The effects of these obtained compounds on nitric oxide (NO) production induced by lipopolysaccharide (LPS) in RAW 264.7 cells were evaluated.(10R*,13R*,15R*)-15,16-Epoxy-6,13-dihydroxy-15-methoxy-labda-5,8-dien-7-one inhibited NO production with an IC₅₀ value of 40.1 μM.