trans-Tiliroside: A potent alpha-glucosidase inhibitor from the leaves of Elaeagnus angustifolia L

Elaeagnus angustifolia L. (Elaeagnaceae) is an important medicinal plant associated with numerous pharmacological activities. Its leaves are used as a therapeutic agent in traditional medicinal systems to treat diabetes. However, the active compounds responsible for the beneficial effects of E. angustifolia remain unclear. In this study, we determined the bioactive profile of E. angustifolia leaves using open column chromatography and semipreparative HPLC. Further, we sought to determine its a-glucosidase and a-amylase inhibitory activities, and its DPPH and ABTS radical-scavenging activities. Four undescribed flavonol glycosides, igdoside A-D, and four known glucosides were isolated from the ethyl acetate and n-butanol extracts of E. angustifolia leaves. Thereafter, the compound structures were identified using spectroscopic methods, including NMR and mass spectrometry. Of the compounds extracted, kaempferol 3-O-(6 ''-trans-p-coumaroyel)-beta-D-glucopyranoside (trans-tiliroside), exhibited the highest alpha-glucosidase inhibitory activity with an IC50 value of 2128 +/- 63 mu M compared to the positive control, acarbose (IC50 = 6561 +/- 207 mu M). trans-Tiliroside was also found to exhibit potent scavenging activity against the ABTS radical, with an IC50 value of 5 +/- 0 mu M, compared to the positive controls, trolox (31 +/- 1 mu M) and alpha-tocopheml (50 +/- 1 mu M). In addition, isorhamnetin-3-beta-D-galactopyranoside (IC50 = 6 +/- 0 mu M) and astragalin (IC50 = 6 +/- 0 mu M) showed similar ABTS radical-scavenging activity as transtiliroside. Based on HPLC, the content of trans-tiliroside was 9.69% in the ethyl acetate extract, 1.04% in decoction, 0.34% in 70% methanol extract, and 0.23% in infusion. None of the extracts and compounds showed alpha-amylase inhibition or DPPH-scavenging activity.