Sesquiterpenoids from the Aerial Parts of Inula japonica

Fourteen sesquiterpenoids with an eudesmane C‐atom skeleton, including four new ones, (1 β ,5 α ,7 β ,8 β ,11 β )‐5‐hydroperoxy‐1‐hydroxyeudesm‐4(15)‐eno‐12,8‐lactone ( 1 ), (1 β ,5 α ,7 β ,8 β )‐8‐(acetyloxy)‐5‐hydroperoxy‐1‐hydroxycostic acid methyl ester ( 12 ), and a mixture of (1 β ,3 β ,4 β ,7 β ,8 β )‐1,3‐dihydroxyeudesma‐5,11(13)‐dieno‐12,8‐lactone ( 7 ) and (1 β ,3 β ,4 β ,7 β ,8 β ,11 β )‐1,3‐dihydroxyeudesm‐5‐eno‐12,8‐lactone ( 8 ), were isolated from the aerial parts of Inula japonica (Asteraceae). Their structures were determined by extensive spectroscopic methods, and those of 7 and 12 confirmed by means of single‐crystal X‐ray diffraction analysis.