Secondary metabolites from the flower buds of Lonicera japonica and their in vitro anti-diabetic activities.

Four new compounds (1, 2, 7 and 8) and twenty known compounds were isolated from the flower buds of Lonicera japonica. Their structures were determined by extensive NMR and HR-ESIMS spectroscopic data analyses. Among them, compounds 1 and 2 are a pair of diastereoisomers possessing a rare chemical structure, and their absolute configurations were determined by comparing their experimental and calculated ECD spectra. Furthermore, all the isolates were evaluated for their inhibitory effects on α-glucosidase and protein tyrosine phosphatase 1B (PTP1B), especially 1 and 2, which displayed both significant inhibitions. In addition, the possible action mechanism of the active compounds was also explored by using molecular docking studies.