Anti-Inflammatory and α-Glucosidase Inhibitory Triterpenoid with Diverse Carbon Skeletons from the Fruits of Rosa roxburghii

The fruits of Rosa roxburghii Tratt. are edible nutritional food with high medicinal value and have been traditionally used as Chinese folk medicine for a long time. In this study, 26 triterpenoids including four new pentacyclic triterpenoids, roxbuterpenes A–D (1, 4, 5, and 24), along with 22 known analogues (2, 3, 6–23, 25, and 26), were isolated from the fruits of R. roxburghii. Their chemical structures were determined on the basis of extensive spectroscopic analyses (including IR, HRESIMS and NMR spectroscopy). The absolute configuration of roxbuterpene A (1) was determined by an X-ray crystallographic analysis. This is the first report of the crystal structure of 5/6/6/6/6-fused system pentacyclic triterpenoid. Notably, roxbuterpenes A and B (1 and 4) possessed the A-ring contracted triterpenoid and nortriterpenoid skeletons with a rare 5/6/6/6/6-fused system, respectively. Compounds 1–7, 11, 13–15, 18–20, 24, and 25 exhibited moderate or potent inhibitory activities against α-glucosidase. Compounds 2, 4, 6, 11, and 14 showed strong activities against α-glucosidase with IC50 values of 8.4 ± 1.6, 7.3 ± 2.2, 13.6 ± 1.4, 0.9 ± 0.4, and 12.5 ± 2.4 μM, respectively (positive control acarbose, 10.1 ± 0.8 μM). Compounds 13, 14, and 16 moderately inhibited the release of NO (nitric oxide) with IC50 values ranging from 25.1 ± 2.0 to 51.4 ± 3.1 μM. Furthermore, the expressions of TNF-α (tumor necrosis factor-α) and IL-6 (interleukin-6) were detected by ELISA (enzyme-linked immunosorbent assay), and compounds 13, 14, and 16 exhibited moderate inhibitory effects on TNF-α and IL-6 release in a dose-dependent manner ranging from 12.5 to 50 μM.