Anti-inflammatory labdane diterpenoids from the aerial parts of Leonurus sibiricus

Eleven undescribed labdane diterpenoids, sibiricusins K-U, and seven known analogues were obtained from the MeOH extract of the aerial parts of Leonurus sibiricus. The structures of the compounds were established by detailed spectroscopic data analysis, single-crystal X-ray diffraction analysis and ECD calculations. Among them, sibiricusins L-N featured a rare α, β-unsaturated-γ-lactam moiety. Fourteen of the isolates were evaluated for their anti-inflammatory effect on the production of NO in LPS-induced RAW264.7 cells through Griess assay. Sibiricusin O displayed the strongest activity with an IC₅₀ value of 9.0 ± 1.7 μM.