Iridoid constituents from the branches of Viburnum chinshanense and their inhibitory effects on α-amylase and α-glucosidase

Ten previously undescribed iridoid constituents, viburnshosins A-E (1-5) and viburnshosides A-E (6-10), together with one known analogue (11), were isolated from the branches of Viburnum chinshanense. Their structures were unambiguously elucidated by a comprehensive analysis of 1D and 2D NMR data, together with HRESIMS spectroscopic data. The absolute configurations of compounds 1-10 were assigned by means of the calculated ECD spectra. Interestingly, compounds 2 and 3 are the first iridoids with an unusual C-3-C-7 oxo bridge. Compounds 4, 5, and 10 displayed remarkable inhibitory effects against alpha-amylase (IC50: 38.42, 37.65, and 21.64 mu M, respectively) and alpha-glucosidase (IC50: 12.97, 19.34, and 25.71 mu M, respectively), comparable to those of the positive control acarbose (IC50: 39.75 and 23.66 mu M, respectively). The interaction modes of compounds 4 and 10 with two enzymes were analyzed by molecular modeling.