Phenolic constituents from Rhododendron anthopogonoides and their bioactivities

Rhododendron anthopogonoides, an important medicinal plant, has been historically used in both traditional Chinese medicine and Tibetan folk medicine. The first phytochemical investigation on the water-soluble fraction of its leaves and twigs led to the isolation of seven new aromatic glycosides, named anthopogosides A-G (1-7), together with 15 known compounds (8-22). Their chemical structures and absolute configurations were unambiguously elucidated by comprehensive spectroscopic analysis (NMR and HRMS) and quantum chemical calculations (NMR and ECD). Compounds 3-5, 15, 16, and 21 showed significant anti-inflammatory activity at the concentration of 40 μM. Compound 10 exhibited the most potent DPPH and ABTS free radical scavenging capacities with IC₅₀ values 29.46 ± 0.07 and 79.10 ± 1.07 μM, respectively. In addition, flavonoid trimers 20 and 22 displayed outstanding α-glucosidase inhibitory activity with IC₅₀ values of 0.48 ± 0.02 and 0.47 ± 0.02 μM, which were 700-fold higher than that of the positive control acarbose. These findings could greatly enrich the chemical diversity of water-soluble constituents from Rhododendron species and highlighted their potential applications.