A new labdane-type diterpenoid from Leonurus japonicus

Five fractions prepared from the crude extract of Leonurus japonicus were examined in order to determine their cytotoxic potential. Under the bioassay guidance, a new labdane-type diterpenoid (1), and nine known ones (2–10) along with a seco-labdane (11) were isolated from the aerial parts of Leonurus japonicus. The structure elucidation was primarily based on comprehensive spectroscopic analyses, including HRESIMS, IR, and 1D and 2D NMR methods. Compound 4 (6β-hydroxy-15,16-epoxylabda-8,13(16),14-trien-7-one) exhibited potential cytotoxicity against HeLa cell line (IC₅₀ = 23.75 μM).