Iridoids from Cornus officinalis Siebold & Zucc and their alpha-glucosidase inhibitory activity

Four new iridoid glycosides, cornoidosides A-D (1-4), along with 35 analogues (5-39), were isolated from the dried fruits of Cornus officinalis Siebold & Zucc. The chemical structures of them were elaborated by extensive spectroscopic means, including 1D, 2D-NMR, HR-ESI-MS and computational chemistry. Compound 4 was the first dimeric iridoid consisting of sweroside and α-morroniside moiety from C. officinalis. The effect of 1-39 against α-glucosidase activity was tested in vitro. Compounds 7-β-O-ethylmorroniside (10), 7-ketologanin (14) and 8-epiloganin (15) (IC₅₀: 37.8, 40.6 and 19.3 μM, respectively) showed moderate activity to suppress α-glucosidase relative to acarbose (IC₅₀ = 81.9 μM). The findings provided some new insights to understand the hypoglycaemic effect of C. officinalis and the development towards the natural α-glucosidase inhibitor.