MEDICINAL FOODSTUFFS .9. THE INHIBITORS OF GLUCOSE-ABSORPTION FROM THE LEAVES OF GYMNEMA-SYLVESTRE R. BR. (ASCLEPIADACEAE) - STRUCTURES OF GYMNEMOSIDE-A AND GYMNEMOSIDE-B

Although the glycosidic fraction from the dried leaves of Gymnema sylv estre R. BR., gymnemic acid, was reported to be effective for diabetes , it showed little inhibitory activity on the increase of serum glucos e level in oral glucose-loaded rats. From the glycosidic fraction, six triterpene glycosides, gymnemosides a, b, c, d, e, and f, were isolat ed together with nine known triterpene glycosides. The structures of g ymnemosides a and b were determined on the basis of chemical and physi cochemical evidence as 21-O-tigloyl-22-O-acetylgymnemagenin 3-O-beta-D -glucopyranosiduronic acid and 16-O-acetyl-21-O-tigloylgymnemagenin 3- O-beta-D-glucopyranosiduronic acid, respectively. In addition, an acet yl group linked to the 16- or 22-hydroxyl group in gymnemosides a and b was found to migrate easily to the primary 28-hydroxyl group, while the acyl migration from the 28-position was rarely observed. The inhib itory activity of each triterpene glycoside from gymnemic acid was exa mined to determine its impact on the increase of serum glucose level i n oral glucose-loaded rats. Gymnemoside b and gymnemic acids III, V, a nd VII were found to exhibit a little inhibitory activity against gluc ose absorption, but the principal constituents, gymnemic acid I and gy mnemasaponin V, lacked this activity.