The ethanolic extract of the leaves of Eriobotrya japonica exhibited inhibitory activity against phosphodiesterase-4D (PDE4D), which is a therapeutic target of inflammatory disease. Subsequent bioassay-guided fractionation led to the isolation of a new triterpene (1), together with seven known triterpenoids, methyl corosolate (2), ursolic acid (3), oleanolic acid (4), methyl maslinate (5), α-amyin (6), 3β,19α,23-trihydroxy-urs-12-ene (7) and uvaol (8). The structure of compound 1 was established as 3β-hydroxyl-21β-acetoxyl-urs-12-en-28-carboxylate on the basis of interpretation of its 1D and 2D NMR and HR-ESI-MS spectroscopic data. The bioassay results verified compounds 2, 3 and 8 inhibited PDE4D2 effectively with the IC50 values of 3.06, 2.18 and 5.17 μM, respectively, which may provide a novel mechanism for the anti-inflammatory activity of the leaves of E. japonica.
Keywords: Eriobotrya japonica; PDE4 inhibitors; triterpenoid.