Two undescribed sesquiterpene lactones, tithdiverolides A and B (1 and 2), and a rare meroterpene lactone, tithdiverolide C (3), as well as seven known sesquiterpenoids (4-7) and monoterpenoids (8-10), were obtained from Tithonia diversifolia (Asteraceae). Structural identification of these compounds relied on a synergistic combination of spectroscopic and computational methods, including NMR, HRESIMS, GIAO NMR calculations with DP4+ probability analysis, and ECD calculations. Chemically, compounds 1 and 2 were eudesmane and cadinane sesquiterpene lactones, respectively, while compound 3 was a rare meroterpene lactone possessing monoterpenoid-methyl ketone hybrid. Biologically, compound 3 exhibited NO inhibitory activity with an IC50 of 33.5 ± 1.3 µM.
Wang et al. (Sun,) studied this question.