Triterpenes

Triterpenes represent a comprehensive group of natural substances that occur in both animals and plants. Biogenetically, tripterpenes are derived from isoprene and are composed of 6 isoprene units or 3 terpene units (see terpenes below). One isoprene unit consists of 5 carbon atoms each.

The vast majority of triterpenes are composed of tetra- and pentacyclic compounds which are altered by cleavage and attachment of carbon atoms as well as by incorporation of heteroatoms (e.g. nitrogen: example: steroidal alkaloids) etc. An aliphatic (not composed of cyclic compounds) representative of the triterpenes is the hydrocarbon squalene. Triterpenes can be present in plants as secondary plant substances either in free form or as aglycons of triterpene saponins. Many triterpenes have important biological functions, e.g. as hormones.

The tetracyclic triterpenes (lanosterane type) include the important group of steroid hormones; furthermore sterols (syn.= sterols) such as cholesterol (syn.: cholesterol) or mycosterols (ergosterone or ergosterol as a precursor of vitamin D) as well as bile acids (see table).

Pentacyclic triterpenes are found e.g. as triterpene alcohols and triterpene acids in resins (resino acids and resinole) or as triterpene sapogenins (saponins).

Terpenes with 5 carbon atoms are called hemiterpenes (C5), with 10 monoterpenes (C10), with 15 sesquiterpenes (C15), with 20 diterpenes (C20), with 25 sesterterpenes (C25), with 30 triterpenes (C30) and with 40 tetraterpenes (C40). Terpenes with more than 8 isoprene units thus have > 40 carbon atoms; they are called polyterpenes.

Many triterpenes are found in cosmetic products but also in some drugs (e.g. cardiac glycosides like digitoxin).

As triterpenes belong to the lipids they are not soluble in cold water but only in hot water and alcohol. Thus, triterpenes are also not components of essential oils.