Terpenoids from the Roots of Ligularia muliensis

Three new eremophilane‐type sesquiterpenes, (6 β ,8 α )‐6‐(acetyloxy)‐8‐hydroxyeremophil‐7(11)‐en‐12,8‐olide ( 1 ), (6 α ,8 α )‐6‐hydroxyeremophil‐7(11)‐en‐12,8‐olide ( 2 ), and (6 α ,8 α )‐6‐(acetyloxy)eremophil‐7(11)‐en‐12,8‐olide ( 3 ) ((8 α )‐eremophil‐7(11)‐en‐12,8‐olide = (4a R ,5 S ,8a R ,9a S )‐4a,5,6,7,8,8a,9,9a‐octahydro‐3,4a,5‐trimethylnaphtho[2,3‐ b ]furan‐2(4 H )‐one), besides the recently elucidated eremoligularin ( 4 ) and bieremoligularolide ( 5 ), as well as a new highly oxygenated monoterpene, rel‐ (1 R ,2 R ,3 R ,4 S ,5 S )‐ p ‐menthane‐1,2,3,5‐tetrol ( 12 ), together with six known constituents, i.e. , the sesquiterpenes 6 and 7 , the norsesquiterpenes 8 – 10 , and the monoterpene 13 , were isolated from the roots of Ligularia muliensis. In addition, an attempt to dimerize 1 to a bieremophilenolide ( Scheme ) resulted in the generation of the new derivative (6 β ,8 β )‐6‐(acetyloxy)‐8‐chloroeremophil‐7(11)‐en‐12,8‐olide ( 11 ). The new structures were established by means of detailed spectroscopic analysis (IR, FAB‐, EI‐, or HR‐ESI‐MS as well as 1D‐ and 2D‐NMR experiments). Compounds 4 and 5 were evaluated for their antitumor effects in vitro ( Table 3 ).