Proof of the Structure and Stereochemistry of α-Amyrin by Synthesis from a β-Amyrin Derivative, Glycyrrhetic Acid^1,2

Revisited After 50 Years: The “Stereochemical Interpretation of the Biogenetic Isoprene Rule for the Triterpenes”

“…At the time of the writing of the Helvetica Chimica Acta paper, a number of questions concerning the structure of ring E in a-amyrin were still open. The remaining gaps were filled first through the identification of a monocyclic degradation product, which confirmed the six-membered nature of this ring and allowed the determination of the (20R)-configuration of the starting material [99], and soon thereafter by a partial synthesis of the triterpene from glycerrhetic acid [100], which confirmed the correctness of the Corey-Ursprung proposal (cf. XXVI in Scheme 5 of [3]).…”

Glycyrrhetic acid (a review)

“…The Structure of Glycyrrhetic Acid GTA was originally isolated by Tschirch and Gederberg [4] by the hydrolysis of GZA (II), the main glycoside of the licorice root extract. Subsequent investigations performed by several groups of researchers, including Ruzicka et al [5], Djerassi and Foltz [6], Beaton and Spring [7], and Corey and Cantrall [8], allowed the GTA structure to be identified as 313,2013-3-hydroxy-11-oxo-12-oleanen-29-oic acid. The data related to the GTA structure identification were reviewed in [9].…”