Isomeric eremophilane lactones from Senecio tsoongianus.

From the whole plant of Senecio tsoongianus, two pairs of epimers, tsoongianolides A (1) and B (2), and tsoongianolides C (3) and D (4), and two new sesquiterpene lactones, tsoongianolides E (5) and F (6), all of which possess the eremophilane skeleton, were isolated. Two known eremophilane dimers (7) and (8) were also obtained from this species. Their absolute structures were elucidated by 1D- and 2D-NMR techniques and by X-ray diffraction studies, along with chemical evidence.