Sesquiterpenoids and lactone derivatives from Ligularia dentata

Seven new compounds were isolated from the roots of Ligularia dentata, including five bisabolane-type sesquiterpenoids (bisabolane=1-(1,5-dimethylhexyl)-4-methylcyclohexane), namely (8 beta,10 alpha)-8(angeloyloxy)-5,10-epoxybisabola-1,3,5,7(14)-tetraene-2,4,11-triol (1), (8 beta,10 alpha)-8-(angeloyloxy)-5,10-epoxythiazolo[5,4-alpha]bisabola-1,3,5,7(14)-tetraene-4,11-diol (2), (1 alpha,2a,3 beta,5 alpha,6 beta) - 1,5,8-tris (angel oyl oxy)-10,11-epoxy-2,3-dihydroxybisabol-7(14)-en-4-one (3), (1 alpha,2 alpha,3 beta,5 alpha,6)-2],5,8-tris(angeloyloxy)10, 11 -epoxy- 1,3-di hydroxybisabol -7(14)-en-4-one (4), and (1 alpha,2 beta,3 beta,5 alpha,6 beta)-1,8-bis(angeloyloxy)-2,3epoxy-5,10-dihydroxy-11-methoxybisabol-7(14)-en-4-one (5) (angeloyloxy [(2Z)-2-methyl-l-oxobut2-enyl]oxy), and two lactone derivatives, (2 alpha,3 beta,5 alpha)-2-(acetyloxy)-9-methoxy-5-(methoxycarbonyl)-2,3dimethylheptano-5-lactone (6), and (2 beta,4 beta)-2-ethyl-5-hydroxy-5-(methoxycarbonyl)-4,5-dimethylpentano-4-lactone (7) (alpha/beta denote relative configurations), together with (2E,4R,5S)-2-ethylidene-5-(methoxycarbon yl) -4-methylhexano-5 -lactone (8), a known synthetic compound. Compound 2 is the first sesquiterpenoid derivative containing the uncommon benzothiazole moiety. The structures of 1-8 were established by spectroscopic methods, especially 2D-NMR and MS analyses.