Separation of sesquiterpene glycosides with α-glucosidase inhibitory activity from Eriobotrya japonica (Thunb.) leaves by high-speed countercurrent chromatography

Micro-fraction bioactivity profiling and high speed countercurrent chromatography were performed for screening and isolation of components with α-glucosidase inhibitory activity from Eriobotrya japonica (Thunb.) leaves. Three sesquiterpene glycosides and a number of known pentacyclic triterpene acids, including a new compound, were successfully screened. Sesquiterpene glycosides were found to have α-glucosidase inhibitory activity for the first time. An efficient strategy for preparative separation of the three sesquiterpene glycosides from E. japonica leaves by column chromatography combined with two-step high speed countercurrent chromatographic separation was established. Two biphasic solvent systems, including n-hexane-ethyl acetate-methanol-water (5:95:5:95, v/v) and ethyl acetate-ethanol-water (100:20:80, v/v), were selected. In the first countercurrent chromatographic separation, 17.50 mg of sesquiterpene glycoside 1 with 92.9% purity and 15.11 mg of sesquiterpene glycoside 3 with 94.4% purity were isolated from 80.10 mg of partially purified fraction I, and in the second separation, 4.42 mg of new sesquiterpene glycoside 2 with 94.9% purity were isolated. Each screened compound was evaluated by α-glucosidase inhibition assay, and results showed that the new sesquiterpene glycoside 2 had high inhibitory activity with IC₅₀ = 7.83±0.01 μM.