Chemistry, Distribution and Biological Activities of 13,28-Epoxy-Oleanane Saponins from the Plant Families Myrsinaceae and Primulaceae

Saponins are a very diverse and large group of natural compounds, consisting of a glycan moiety linked to a triterpene or a steroid sapogenin. Part of these contain a 13,28-epoxy bridge, where C-28 can be a methylene, a hydroxymethylene or a carbonyl group. This review was restricted to those saponins possessing a completely saturated pentacyclic triterpene skeleton and a 13,28-epoxy bridge, in which C-28 was a methylene or a hydroxymethylene group, excluding the C-28 carbonyl derivatives (28→13 lactones). Almost all of these saponins have been found in members of the Primulaceae or Myrsinaceae plant families. The most important genera were Ardisia, Maesa, and Myrsine from the Myrsinaceae, and Cyclamen, Lysimachia, and Primula from the Primulaceae. Their structures were reviewed, biological activities discussed, and structure-activity relationships established.