Iridoid glycosides from the flower buds of Lonicera japonica and their nitric oxide production and α-glucosidase inhibitory activities

The flower buds of Lonicera japonica are commonly used as popular healthy beverages that are also effective in the prevention and cure of a variety of chronic diseases, such as diabetes, and also as an anti-inflammatory treatment for thousands of years. In this study, three new iridoid glycosides along with twenty-five known analogues were isolated from the aqueous extract of L. japonica. Their structures were determined by extensive 1D NMR, 2D NMR and HR-ESIMS spectroscopic data analyses, and all the isolates were investigated with regard to lipopolysaccharide (LPS)-induced nitric oxide (NO) production and alpha-glucosidase inhibitory effects. Among these compounds, 12 and 13 exhibited strong NO inhibitory activities and no cytotoxic effects. Moreover, most compounds were potent alpha-glucosidase inhibitors compared with the positive control acarbose. These findings will enhance knowledge about the bioactive components of L. japonica and help promote its potential application in functional foods. (C) 2015 Elsevier Ltd. All rights reserved.