Phytoconstituents from the leaves of Viburnum cylindricum Buch. -Ham. ex D. Don and their enzyme inhibitory activities

Viburnum cylindricum Buch. -Ham. ex D. Don is abundant in bioactive secondary metabolites with promising functions such as anti-inflammation and anti-diabetes. In this work, the polyphenolic extract of V. cylindricum leaves (VCLP) exhibited significant inhibition on α-glucosidase and urease activity. Two previously undescribed phenolic glycosides (1, 2) and fourteen known analogues (3-16) were isolated from VCLP, which were determined by spectroscopic analyses and chemical methods. The bioactivity assessment revealed that compounds 3, 4, 8, 14, and 16 could potently inhibit α-glucosidase activity with IC₅₀ values ranging from 20.83 to 28.52 μM compared to acarbose (IC₅₀ = 29.71 μM) (p < 0.05). In addition, compounds 3 and 4 showed significant urease inhibition with IC₅₀ values of 10.73 and 7.61 μM, respectively, comparable to thiourea (IC₅₀ = 28.57 μM) (p < 0.05). Moreover, the molecular docking analysis elucidated the binding mechanisms between these bioactive compounds and the enzymes α-glucosidase and urease.