Triterpenoid Glycosides from Olax imbricata

Introduction: Olax imbricata, owning antibacterial, antioxidant, and anti-inflammatory activities, has been investigated as one of traditional diabetic plants in Vietnam. In our previous publications on Olax imbricata, the structure analysis of the isolated compounds were reported, including two phenolic compounds, three phenolic glycosidic compounds, a sesquiterpenoid tropolone and 1,2,3,4-tetrahydronaphthalene derivatives. This article described the isolation and structure elucidation of three triterpenoid glycosides isolated from the methanol extract of Olax imbricata growing in Phu Yen province. Additionally, the evaluation of inhibitory activity for a-glucosidase was performed on a pure compound. Method: The methanol extract of this plant applied the chromatographic techniques, including thin-layer chromatography and silica gel column chromatography, led to the isolation of three pure compounds. The structures of three isolated compounds were elucidated by the spectroscopic data, including 1D and 2D NMR spectra in a combination of HRESIMS, and the sugar moieties were elucidated by acid hydrolysis. The a-glucosidase inhibitory assay was applied to a pure compound by the colorimetric method. Results: Three triterpenoid glycosides, namely 3-O-a-L-rhamnopyranosyl-(1->4)-b -D-glucopyranosyl-(1->3)-6′- O-ethyl-b -Dglucuronyl oleanolic acid (1), oleanolic acid 28-O-b -D-glucopyranoside (2) and spergulacin (3) were isolated and elucidated. The compound 2 showed its strong potentiala-glucosidase inhibitory activity with the IC50 value of 56.15+/-1.31 mM. Conclusion: Among them, compound 1 is a new one, the compounds 2 and 3 were isolated for the first time from the genus Olax. The compound 2 exhibited the potential a-glucosidase inhibition activity, contributing to demonstrating the diabetes treatment ability of Olax imbricata in the folklore.