Structures and Biological Activities of Polyacylated ent-Kaurane Diterpenoid Glycosides from the Aerial Parts of Inula hupehensis

Sixteen new (1–16) and three known (17–19) polyacylated ent-kaurane diterpenoid glycosides were isolated from the aerial parts of Inula hupehensis. The planar structures of 1–16 and their relative configurations were established on the basis of extensive spectroscopic analysis. The absolute configurations of all stereogenic centers for compounds 1 and 6 were determined by single-crystal X-ray diffraction experiments, and the absolute configurations of the other new compounds were assigned by chemical degradation and experimental ECD data. Antineuroinflammatory testing of all the isolates showed that compound 5 inhibited lipopolysaccharide-induced nitric oxide production in BV-2 microglial cells with an IC50 value of 15.6 μM. In an α-glucosidase inhibitory assay, compound 13 exhibited a strong inhibitory effect with an IC50 value of 32.8 μM, whereas the IC50 value of the positive control, acarbose, was 387.8 μM.