LC-MS guided isolation of phenolic glycosides from Viburnum luzonicum Rolfe leaves and their α-amylase and α-glucosidase inhibitory activities

Viburnum luzonicum Rolfe is widely used in China as folk medicine. The bioactivity evaluation indicated that the n-BuOH fraction of V. luzonicum leaves (VLLB) could significantly inhibit alpha-amylase and alpha-glucosidase. In order to clarify its active constituents, the phytochemical analysis on VLLB was first performed using HPLC-QTOF-MS/MS, and three new phenolic compounds, viburosides A-C (1-3), along with seven known analogues (4-10) were isolated through preparative HPLC. The undescribed compounds were determined by extensive spectroscopic analyses (H-1 and C-13 NMR, HSQC, HMBC, HRESIMS, and ORD) and enzymatic hydrolysis. In the in vitro enzyme assays, compounds 1-8 showed potent alpha-amylase and alpha-glucosidase inhibitory activities. The enzymatic kinetics and molecular docking of the strongest inhibitors 2 and 3 against the corresponding target enzyme were also performed.