Four undescribed iridoid glycosides with antidiabetic activity from fruits of Cornus officinalis Sieb. Et Zucc.

Four novel iridoid glycosides neocornuside E-H (1-4), together with nine known ones (5-13), were isolated from fruits of Cornus officinalis. Their chemical structures were determined on the basis of spectroscopic analyses and comparing of the literature data. All of the isolated compounds were evaluated for their antidiabetic activity in insulin resistant HepG2 cells. Compounds 2, 4, 5, 8, and 12 exhibited antidiabetic activities with EC50 values of 40.12, 2.54, 70.43, 15.31, and 4.86 mu M, respectively. Flow Sight cytometry analysis indicated that compounds 2, 4, 5, 8, and 12 improved the ability of 2-NBDG uptake of insulin-induced HepG2 cells.