3.8 Biosynthesis of Saponin Glycosides
Saponins are usually of two types, namely: first, the steroidal saponins which essentially have a spiroketal side chain, and secondaly, the triterpenoid saponins. It has been proved that labelled acetate and mevalonate are duly incorporated into spiroketal steroids as well as pentacyclic triterpenoids. It is, however, pertinent to mention here that the major pathway adopted by both types of sapogenins is more or less identical and that it involves head to tail coupling of various acetate units. It is asumed that a branching takes place most probably after the formation of the triterpenoid hydrocarbon squalene, that ultimately leads to the spiroketal steroids in one direction and to the pentacyclic triterpenoids in the other as shown below:
