triterpene
{{Short description|Class of chemical compounds}}
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| caption1 = Squalene: One of the most important triterpenes
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| caption2 = Hopane: An example of a pentacyclic triterpene
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Triterpenes are a class of terpenes composed of six isoprene units with the molecular formula C30H48; they may also be thought of as consisting of three terpene units. Animals, plants and fungi all produce triterpenes, including squalene, the precursor to all steroids.{{cite book|title=Terpenes: Flavors, Fragrances, Pharmaca, Pheromones|chapter=Triterpenes|author=Eberhard Breitmaier|year= 2006|pages=86–108 |isbn=9783527609949 |doi=10.1002/9783527609949.ch6}}{{cite journal|title=Cyclization Enzymes in the Biosynthesis of Monoterpenes, Sesquiterpenes, and Diterpenes|author1=Davis, Edward M. |author2=Croteau, Rodney |journal=Topics in Current Chemistry|year=2000|volume=209|pages=53–95|doi=10.1007/3-540-48146-X_2|isbn=978-3-540-66573-1 }}
==Structures==
Triterpenes exist in a great variety of structures. Nearly 200 different skeletons have been identified.{{cite journal|last1=Xu|first1=Ran|last2=Fazio|first2=Gia C.|last3=Matsuda|first3=Seiichi P.T.|title=On the origins of triterpenoid skeletal diversity|journal=Phytochemistry|date=February 2004|volume=65|issue=3|pages=261–291|doi=10.1016/j.phytochem.2003.11.014|pmid=14751299 }} 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 two farnesyl 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 bacterial hopanoids and eukaryotic sterols.
Triterpenoids
By definition triterpenoids are triterpenes that possess heteroatoms, usually oxygen. The terms triterpene and triterpenoid often are used interchangeably.
Triterpenoids possess a rich chemistry and pharmacology with several pentacyclic motifs. Lupane, oleanane and ursane show particular promise as anti-cancer agents.{{cite journal |pages=1549–60 |doi=10.1055/s-0029-1186102 |title=Pentacyclic Triterpenes of the Lupane, Oleanane and Ursane Group as Tools in Cancer Therapy |year=2009 |last1=Laszczyk |first1=Melanie |journal=Planta Medica |volume=75 |issue=15 |pmid=19742422|doi-access=free }}{{cite journal|last1=Liu|first1=Jie|title=Pharmacology of oleanolic acid and ursolic acid|journal=Journal of Ethnopharmacology|date=December 1995|volume=49|issue=2|pages=57–68|doi=10.1016/0378-8741(95)90032-2|pmid=8847885}}
=Steroids=
Steroids feature a cucurbitane core, although in practice they are biosynthesised from either lanosterol (animals and fungi) or cycloartenol (plants) via the cyclization of squalene. Steroids have two principal biological functions, being either key components of cell membranes or signaling molecules that activate steroid hormone receptors. Important sub-classes include sterols and cucurbitacins.
=Triterpenoid saponins=
Triterpenoid saponins are triterpenes which belong to the saponin group of compounds, making them triterpenoid glycosides. They are produced by plants as part of their self-defense mechanism{{cite journal|last1=Augustin|first1=Jörg M.|last2=Kuzina|first2=Vera|last3=Andersen|first3=Sven B.|last4=Bak|first4=Søren|title=Molecular activities, biosynthesis and evolution of triterpenoid saponins|journal=Phytochemistry|date=April 2011|volume=72|issue=6|pages=435–457|doi=10.1016/j.phytochem.2011.01.015|pmid=21333312}} with important sub-classes including ginsenosides{{cite journal|last1=Attele|first1=Anoja S|last2=Wu|first2=Ji An|last3=Yuan|first3=Chun-Su|title=Ginseng pharmacology|journal=Biochemical Pharmacology|date=December 1999|volume=58|issue=11|pages=1685–1693|doi=10.1016/S0006-2952(99)00212-9|pmid=10571242}} and eleutherosides.