New olean-15-ene type gymnemic acids from Gymnema sylvestre (Retz.) R.Br. and their antihyperglycemic activity through α-glucosidase inhibition

A mixture of gymnemic acids was precipitated from the water extract of leaves of Gymnema sylvestre (Retz.) R.Br. ex Sm. (Asclepiadaceae) by acidification with 2 N H2SO4. The chromatographic separation of the mixture afforded five new gymnemic acids (1-5). The compounds were characterized as Δ15 oleanane glycosides on the basis of extensive spectral data analysis. The compounds (1-5) showed dose dependent inhibition of α-glucosidase, which was...