Isolation and Structure Elucidation of Gymnemic Acids, Antisweet Principles of Gymnema sylvestre

The structure of gymnemagenin (3/?,16/?,21/?,22a,23,28-hexahydroxy-olean-l 2-ene), the sapogenin of the antisweet principles of Gymnema sylvestre, was established by X-ray analysis of the 3/?,23;21/?,22a-di-0~isopropylidene derivative. On the basis of this result, the structure of deacylgymnemic acid was elucidated as the 3-0-/?-glucuronide from the carbon-13 nuclear magnetic resonance spectra. Five antisweet principles, gymnemic acid-IIl, -IV, -V, -VIII, and -IX, were isolated in pure states from the hot water extract of leaves of Gymnema sylvestre. Of these, three (GA-III, -IV, and -V) were known, while two (GA-VIII and -IX) were new compounds. The structures of GA-VIII and -IX were elucidated as 3'-O-/?-D-ara£i7f0-2-hexulopyranosyl gymnemic acid-III and -IV, respectively.