Saponins, acid-catalyzed hydrolysis

Acetoxyacid esters, hydrolysis, Candida utills, 51-54 2-Acetylthiazolidine, recovery efficiency, 72 Acid-catalyzed hydrolysis of saponins, 15,19 Alcohols... 

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. 

Treatment of (11) with cone. HCl at room temperature yielded (10). Furthermore, catalytic hydrogenation of the saponin mixture in ethanol-acetic acid followed by hydrolysis with dilute mineral acid did not yield (1) but afforded the dihydro derivative (12). This evidence indicated that (1) and (10) must be artifacts formed during the process of acid hydrolysis thus, at that stage, the genuine sapogenin seemed to be substance (11) which was named protopanaxadiol (9,10,11). However, as will be described later, investigation of the acid-catalyzed isomerization of dammarane type triterpenes and subsequent study of the mild hydrolysis of the purified... 

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