Isolation and structural elucidation of the herbicidal active compounds from Ligularia stenocephala M.

Screening was conducted using 200 kinds of plant extracts to explore herbicide-activated components of plant origin. We separated and purified active substances and elucidated chemical structures using Ligularia stenocephala M., which has strong activity and has not yet been studied. When the solvent fractions of the leaves of Ligularia stenocephala M. were tested for their herbicidal activity, ethyl acetate and chloroform layer showed an inhibition rate of 95.2% and 94.1%, respectively. In particular, the chloroform layer exerted more than 50% herbicidal activity at 10 ppm. From the chloroform layer with the highest herbicidal activity, we isolated three herbicidal active compounds using stepwise chromatography, specifically silica gel or octadecyl silica (ODS) column chromatography, Sep-pak cartridges, and high performance liquid chromatography (HPLC). Based on the analysis of the active compounds using electron ionization mass spectroscopy (EI-MS), ¹H-NMR, and ¹³C-NMR, we identified the active compounds as euparin, 5,6-dimethoxy-2-isopropenylbenzofuran, and liguhodgsonal. When the herbicidal activity of the identified compounds was tested, euparin showed selective herbicidal activity for lettuce at 10^-3 M, and both liguhogsonal and 5,6-dimethoxy-2-isoprophenylbenzofuran exerted selective activity for rice and Echinochloa crus-galli.