Gymnemic acid

Gymnemic acids are a class of chemical compounds isolated from the leaves of Gymnema sylvestre (Apocynaceae). They are anti-sweet compounds, or sweetness inhibitors.{{Cite journal | doi = 10.1021/jf60164a011| title = Chemistry and physiological properties of gymnemic acid, the antisaccharine principle of the leaves of Gymnema sylvestre| journal = Journal of Agricultural and Food Chemistry| volume = 17| issue = 4| pages = 704–708| year = 1969| last1 = Stoecklin| first1 = Walter}} After chewing the leaves, solutions sweetened with sugar taste like water.

Chemically, gymnemic acids are triterpenoid glycosides. The central structure is the aglycone gymnemagenin (C₃₀H₅₀O₆).{{Pubchem|10051937}} This is adorned with a sugar such as glucuronic acid and with various ester groups. These variations give rise to the different gymnemic acids.{{Cite journal | doi = 10.1039/C0NP00059K| pmid = 21290067| title = Synthesis, biology and clinical significance of pentacyclic triterpenes: A multi-target approach to prevention and treatment of metabolic and vascular diseases| journal = Natural Product Reports| volume = 28| issue = 3| pages = 543–593| year = 2011| last1 = Sheng| first1 = Huaming| last2 = Sun| first2 = Hongbin}} More than 20 homologs of gymnemic acid are known.{{cite book | author = A. Douglas Kinghorn and Cesar M. Compadre | title = Less common high-potency sweeteners | work = Alternative Sweeteners | edition = 2nd | editor = Lyn O'Brien Nabors and Robert C. Gelardi | publisher = Marcel Dekker | location = New York | date = 1991 | isbn = 0-8247-8475-8}}

Gymnemic acid I has the highest anti-sweet properties. It suppresses the sweetness of most of the sweeteners including intense artificial sweeteners such as aspartame and natural sweeteners such as thaumatin, a sweet protein. The anti-sweet activity is reversible, but sweetness recovery on the tongue can take more than 10 minutes.{{cite journal | doi = 10.1080/10408399209527598| pmid = 1418601| title = Characteristics of antisweet substances, sweet proteins, and sweetness-inducing proteins| journal = Critical Reviews in Food Science and Nutrition| volume = 32| issue = 3| pages = 231–52| year = 1992| last1 = Kurihara| first1 = Yoshie}}