Cadinane-Type Sesquiterpenoids from Heterotheca inuloides: Absolute Configuration and Anti-inflammatory Activity

Eight cadinane-type sesquiterpenoids (1–8) together with some triterpenoids, flavonoids, and sterols were isolated from the aerial parts of Heterotheca inuloides. The structures of the new compounds (1–4) were elucidated on the basis of extensive 1D and 2D NMR spectroscopic data analysis. The structures of the new (1–3) and the known (5–7) sesquiterpenoids were confirmed by X-ray crystallography. The absolute configurations of metabolites 2–5 were determined by comparing their experimental and calculated electronic circular dichroism spectra and confirmed via refinement of the Flack parameter using anomalous X-ray scattering from the oxygen atoms and chemical correlation methods. The sesquiterpenoids were evaluated for their anti-inflammatory potential by applying the TPA-induced mouse ear edema model. The results revealed that some of these metabolites exhibit moderate anti-inflammatory activity. At a dose of 228 μg/ear compound 1 showed 43.14 ± 8.09% inhibition on ear edema, indicating an IC50 > 228 μg/ear.