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 β ,10 α )‐8‐(angeloyloxy)‐5,10‐epoxybisabola‐1,3,5,7(14)‐tetraene‐2,4,11‐triol ( 1 ), (8 β ,10 α )‐8‐(angeloyloxy)‐5,10‐epoxythiazolo[5,4‐ a ]bisabola‐1,3,5,7(14)‐tetraene‐4,11‐diol ( 2 ), (1 α ,2 α ,3 β ,5 α ,6 β )‐1,5,8‐tris(angeloyloxy)‐10,11‐epoxy‐2,3‐dihydroxybisabol‐7(14)‐en‐4‐one ( 3 ), (1 α ,2 α ,3 β ,5 α ,6 β )‐2,5,8‐tris(angeloyloxy)‐10,11‐epoxy‐1,3‐dihydroxybisabol‐7(14)‐en‐4‐one ( 4 ), and (1 α ,2 β ,3 β ,5 α ,6 β )‐1,8‐bis(angeloyloxy)‐2,3‐epoxy‐5,10‐dihydroxy‐11‐methoxybisabol‐7(14)‐en‐4‐one ( 5 ) (angeloyloxy=[(2 Z )‐2‐methyl‐1‐oxobut‐2‐enyl]oxy), and two lactone derivatives, (2 α ,3 β ,5 α )‐2‐(acetyloxy)‐9‐methoxy‐5‐(methoxycarbonyl)‐2,3‐dimethylheptano‐5‐lactone ( 6 ), and (2 β ,4 β )‐2‐ethyl‐5‐hydroxy‐5‐(methoxycarbonyl)‐4,5‐dimethylpentano‐4‐lactone ( 7 ) ( α / β denote relative configurations), together with (2 E ,4 R ,5 S )‐2‐ethylidene‐5‐(methoxycarbonyl)‐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.