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.