Triterpenoids with bioactivities from Oenothera biennis

Phytochemical investigation into the whole plants of Oenothera biennis led to the isolation and identification of 28 triterpenoids, of which oenothebienoids A-G (1-7) are reported for the first time. Oenothebienoids A-D (1-4) have an unnormal 20-epi-ursane type triterpenoid framework, which is rarely documented. To swiftly and precisely differentiate the C-20 configurations, a rule was summarized by analysis of the NMR data from the two pairs of simultaneously obtained C-20 epimers, namely 1/8 and 3/9. A series of bioactive assessments revealed that compounds 13 and 14 show moderate inhibitory activity against α-glucosidase with IC₅₀ values of 5.16 ± 1.08 and 4.24 ± 0.48 μM, respectively. Additionally, compounds 14 and 26 display significant inhibitory activity against IDO1 with IC₅₀ values of 8.47 ± 0.57 and 8.83 ± 0.72 μM, respectively.