Constituents From the Flowers of Viburnum macrocephalum f. macrocephalum and Their α-Amylase and α-Glucosidase Inhibitory Activities.

Phytochemical investigation of the flowers of Viburnum macrocephalum f. macrocephalum (VMM), a sterile horticultural form native to China, led to the isolation of two new cadinane-type sesquiterpenes, viburetones A (1) and B (2), together with fifteen known compounds (3-17). Compounds 1 and 2 represent the first examples of this skeletal type from the genus Viburnum. The structures of the new compounds were elucidated by comprehensive analysis of their 1D and 2D NMR, HRESIMS, and ECD data. All isolates were evaluated for their inhibitory activities against α-amylase and α-glucosidase, key enzymes involved in carbohydrate metabolism. Among them, compound 1 exhibited inhibitory activities against α-amylase (IC50 = 38.20 µM) and α-glucosidase (IC50 = 24.15 µM), comparable to those of acarbose (IC50 = 39.19 and 25.73 µM, respectively). Molecular docking studies suggested that compound 1 bound to the active sites of both enzymes via hydrogen bonding and hydrophobic interactions.