Flavonol Caffeoylglycosides as α-Glucosidase Inhibitors from Spiraea cantoniensis Flower

In the screening experiments for rat intestinal α-glucosidase inhibitors in 218 plants cultivated in the Japanese temperate region, potent maltase-inhibiting activity was found in the extract of flowers of Spiraea cantoniensis. The enzyme assay guided fractionation of the extract led to the isolation of three flavonol caffeoylglycosides, quercetin 3-O-(6-O-caffeoyl)-β-galactoside (1), kaempferol 3-O-(6-O-caffeoyl)-β-galactoside (2), and...