Diterpenoids from Leonurus japonicus

Leonurus japonics Houtt. (Lamiaceae) is an annual or biennial herbaceous plant widely distributed and cultivated in China. Five diterpenoids including two new and three known ones were isolated and identified. The new compounds were elucidated as 1-((2S)-2-(3-(furan-3-yl)propanoyl)-2,6,6-trimethylcyclohexyl)-2-hydroxybutan-1-one (1), and 1-((1S,3R,3aS)-3-(2-(furan-3-yl)ethyl)-3-methoxy-3a,7,7-trimethyloctahydroisobenzo furan-1-yl)propan-1-one (2). The known compounds were identified as seco-labdane (3), 6b-hydroxy-15,16-epoxylabda-8,13(16), 14-trien-7-one (4), and leojaponin (5). The dried and powdered herb of L. japonicus was extracted with 95% EtOH by percolation at room temperature. The solvent was evaporated under reduced pressure at 45°C to yield 7.2 kg viscous syrup, which was dissolved in water and extracted with EtOAc to get 3 kg extract. The EtOAc fraction was suspended in 30% EtOH and allowed to pass through a column packed with AB-8 macroporous resin, then eluted with 50%, 70%, 90%, and 95% EtOH to obtain fractions A-D. Considering the diversity of the isolates, compound 1 might be formed by tautomerization of the retro aldol reaction product 7, and 2 was generated by the reaction of 3 with solvent (MeOH) during the evaporation procedure.