Unusual Sesquiterpene Lactones from Ligularia virgaurea spp. oligocephala

Sesquiterpene lactones, ligulolide A (1) and 6β,8α-dihydroxy-1-oxoeremophila-7(11),9(10)-diene-12,8-olide (2), were isolated from Ligularia virgaurea spp. oligocephala. Their structures were established by analysis of one- and two-dimensional NMR data. The relative stereostructures were determined on the basis of NOESY and single-crystal X-ray experiments. 1 represents a novel sesquiterpene carbon framework, and a possible biosynthetic process...