Saponins common structure, examples

The saponin structure is either of the steroidal (commonly tetracyclic triterpenoids) or pentacyclic triterpenoid type. Triterpenoid saponins are found, for example in Quillaia bark and in liquorice root. Quillaia B.P. is defined as the dried inner part of the bark of Quillaja saponaria and other species of Quillaja and is used as an emulsifying agent. Liquorice, the root of which also contains tiiterpenoid saponins, has long been used in pharmacy as a flavoring agent, demulcent, and mild expectorant. 

Since 1958, Shibata and his successors have conducted chemical studies on the saponins of the crude drug. After many twists and turns, it was determined that the major saponins of Ginseng were not oleanane oligoglycosides which are very common in nature, but that the genuine sapogenins were represented by triterpenes of the dammarane type. This was the first example of the occurrence of dammarane saponins in nature. The complications encountered in the isolation and structure determination were mainly due to an unexpected acid catalyzed epimerization of the tertiary hydroxyl group on c-20 of the carbon skeleton which was followed by cyclization of the side chain. This undesirable reaction accompanied acid hydrolysis of the saponins to the sapogenins. 

Saponins represent a large and structurally diverse class of plant terpenoids and are common chemical constituents of, for example, medicinal herbs. The term... 

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