Flavonol Glycosides from the Leaves of Camellia hirsuta and their α-Glucosidase, α-Amylase, and Advanced Glycation End-Products Inhibitory Effects

Two new flavonol polysaccharides, named hirsutaosides A (1) and B (2) along with six known compounds were identified as follows: cameflavoside A (3), camellikaempferoside A (4), kaempferol 3-O-beta-D-glucopyranoside (5), kaempferol 3-O-alpha-L-rhamnopyranoside (6), quercetin 3-O-alpha-L-rhamnopyranoside (7), and epicatechin (8) were isolated from the leaves of Camellia hirsuta Hakoda & Ninh, Theaceae, a native species of Golden Camellias found in Vietnam. Their structures were identified by combining 1D and 2D-Nuclear magnetic resonance spectroscopy, mass spectrometry, and comparison with existing literature. All compounds were evaluated for their inhibitory effects on alpha-glucosidase and alpha-amylase enzyme. Compounds 1-4 and 8 significantly inhibited alpha-glucosidase with IC50 values ranging from 73.9 +/- 6.0 to 247.6 +/- 10.1 mu M. Compounds 1-4 moderately inhibited alpha-amylsase with IC50 values ranging from 321.5 +/- 18.0 to 460.7 +/- 21.6 mu M. Compounds 1-4 significantly inhibited advanced glycation end-product formation with inhibitory percentages ranging from 51.1 to 62.7% at a concentration of 400 mu M. Furthermore, the study explored the impact of compounds 1-4 on breaking advanced glycation end-products, revealing substantial breaking activity ranging from 68.8 to 79.5% at concentrations of 100 and 400 mu M. This study provides new insights into the anti-diabetic properties of compounds from C. hirsuta.