α-Glucosidase inhibitory effect by the flower buds of Tussilago farfara L.

Methanolic extracts from the medicinal parts of 50 traditional Chinese herbs were tested in screening experiments for rat intestinal alpha-glucosidase. The methanolic extract from flower buds of Tussilago farfara L. (Compositae) showed the highest maltase inhibitory activity, with maltose as a substrate. Enzyme assay-guided fractionation of this extract afforded. 3,4-dicaffeoylquinic acid (1), 3,5-dicaffeoyl-quinic acid (2), 4,5-dicaffeoylquinic acid (3) and rutin (4), and the structures of these compounds were elucidated on the basis of MS and NMR data analyses. Compounds 1, 2 and 3 showed comparative maltase inhibitory activities, and the IC50 values were 0.91 mM, 0.90 mM and 0.89 mM, respectively. Comparison of the activities of 1-3, chlorogenic acid (5), quinic acid (6) and caffeic acid (7) suggested that the number of caffeoyl groups attached to a quinic acid core were important for the potency. Rutin (4) showed moderate activity and inhibited 41 % of maltase activity at a concentration of 1 mM. This is the first report on mammalian alpha-glucosidase inhibition of T farfara and the isolation of 1, 2 and 3 from this herb species. These results suggest a use of the extract of T farfara for antidiabetes. (c) 2007 Elsevier Ltd. All rights reserved.