Triterpenes are a class ofterpenes composed of sixisoprene units with the molecular formula C₃₀H₄₈; they may also be thought of as consisting of threeterpene units. Animals, plants and fungi all produce triterpenes, includingsqualene, the precursor to allsteroids.^[1][2]

Squalene: One of the most important triterpenes

Hopane: An example of a pentacyclic triterpene

Triterpenes exist in a great variety of structures. Nearly 200 different skeletons have been identified.^[3] These skeletons may be broadly divided according to the number of rings present. In general pentacyclic structures (5 rings) tend to dominate.

Squalene is biosynthesized through the head-to-head condensation of twofarnesyl pyrophosphate units. This coupling converts a pair of C15 components into a C30 product. Squalene serves as precursor for the formation of many triterpenoids, including bacterialhopanoids and eukaryoticsterols.

By definition triterpenoids are triterpenes that possessheteroatoms, usually oxygen. The termstriterpene andtriterpenoid often are used interchangeably.

Triterpenoids possess a rich chemistry and pharmacology with several pentacyclic motifs.Lupane,oleanane andursane show particular promise as anti-cancer agents.^[5][6]

Steroids feature acucurbitane core, although in practice they are biosynthesised from eitherlanosterol (animals and fungi) orcycloartenol (plants) via the cyclization ofsqualene. Steroids have two principal biological functions, being either key components of cell membranes or signaling molecules that activatesteroid hormone receptors. Important sub-classes includesterols andcucurbitacins.

Triterpenoid saponins are triterpenes which belong to thesaponin group of compounds, making them triterpenoidglycosides. They are produced by plants as part of their self-defense mechanism^[7] with important sub-classes includingginsenosides^[8] andeleutherosides.