Vernonolide A, a Sesquiterpene Lactone with a Unique Carbon Skeleton from Vernonia cinerea

A novel sesquiterpene lactone derivative, vernonolide A (1), featuring an unprecedented carbon skeleton, along with its plausible biosynthetic precursor, vercinolide I (2), and eight known sesquiterpene lactones (3–10) were isolated and characterized from the whole plants of Vernonia cinerea (L.). The structures of 1 and 2 were elucidated using nuclear magnetic resonance spectroscopic analysis and calculated and experimental electronic circular dichroism spectra. A plausible biosynthetic pathway for 1 was proposed. Notably, compounds 8 and 10 exhibited significant inhibitory effects on tumor necrosis factor-α-induced nuclear factor-κB activity, with IC50 values of 0.95 and 5.57 μM, respectively.