Eremophilane and cadinane sesquiterpenoids from the fruits of Alpinia oxyphylla and their anti-inflammatory activities

The fruits of Alpinia oxyphylla have been used for centuries in China as both edible resources and traditional Chinese medicine. In order to identify structurally interesting and bioactive constituents from the fruits of A. oxyphylla, bioassay-guided fractionation and purification of the crude extracts were performed, which led to the isolation of 38 sesquiterpenoids, including six previously undescribed eremophilane sesquiterpenoids (1-6), six new cadinane sesquiterpenoids (23-24, 26-29), and 26 known analogues (7-22, 25 and 31-38). The structures of these compounds were elucidated by comprehensive spectroscopic data analysis, single crystal X-ray diffraction, quantum chemistry calculations (¹³C-NMR and ECD), and Mo₂(OAc)₄ reaction. Several of the isolated compounds (8, 13, 17, 18, 30, 31 and 35) showed moderate to strong inhibition of the secretion of cytokines (NO, TNF-α and IL-6) in LPS-stimulated BV-2 cells. Furthermore, western blot, immunofluorescence, and real-time PCR assays indicated that 18 could down-regulate the mRNA levels of TNF-α, IL-6, COX-2, and iNOS and the protein expression of COX-2 and iNOS. Meanwhile, 18 was able to partially inhibit the phosphorylation of ERK1/2, JNK, and p38. Thus, the discovery of structurally diverse anti-inflammatory sesquiterpenoids from the fruits of A. oxyphylla in this study could benefit the further development and utilization of this plant.