Oleanane-type triterpenoid sulphates, two new α-glucosidase inhibitors from Elaeocarpus hainanensis

In connection with our interest in the phytochemical investigation of Elaeocarpus hainanensis Oliv. (Elaeocarpaceae) growing in Vietnam, two new sulphated oleanane triterpenes were obtained herein and structurally identified. Based on the combination of the extensive 1D-, 2D NMR and HR ESI MS spectroscopic data analysis, their chemical structures have been elucidated as 1α,3β-dihydroxy-olean-18-ene 1-sulphate (1) and 1α,3β-dihydroxy-olean-12-ene 1-sulphate (2). Notably, compounds 1 and 2 are corroborating the proposition that triterpenoid sulphates serve as chemosystematic markers of the Elaeocarpus genus. Additionally, all these two new compounds 1 and 2 strongly inhibited α-glucosidase in vitro with the respective IC₅₀ values of 3.81 ± 0.33 µM and 21.27 ± 0.48 µM, which were significantly better than that obtained from positive control, acarbose (IC₅₀ 247.73 ± 11.85 µM).