Authors: Prof. Dr. med. Peter Altmeyer, Prof. Dr. med. Martina Bacharach-Buhles

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Last updated on: 29.10.2020

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Isoprene; Isoprenoids; Terpenoids

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Terpenes (named after the tree resin turpentine from which terpenes were originally extracted) are a large, heterogeneous group of naturally occurring chemical compounds that occur as secondary ingredients in organisms. Known are > 8.000 terpenes. Their structure consists of formal isoprene (2-methyl-1,3 butadiene).

Terpenes have no functional groups. However, they can be glycosidically bound or linked with other groups (alcohol, aldehyde, ether, ketone, acid and ester) which then carry functional groups. These functionalized terpenes are called terpenoids. Currently, > 35,000 terpenoids are known. They represent the largest group of natural substances.

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Terpenes, especially mono-, sesqui- and diterpenes, can be obtained from plant (parts) or essential oils by physical methods such as steam distillation, extraction or chromatography (methods used in the perfume industry).

In general, a distinction is made between acyclic, mono-, bi-, tri-, tetra- and pentacyclic terpenes, i.e. molecules without, with one, with two, three, four or five rings. Furthermore, terpenes differ in the number of isoprene units (always 5 carbon atoms each).

Terpenes with 5 carbon atoms are called hemiterpenes (C5),

with 1C5 unit: Monoterpenes (C10): Citral, Iridoids, Camphor

with 3 C5 units:sesquiterpenes (C15) - "sesqui -greek.= one and a half": proazulene

with 4 C5 units: diterpenes (C20): resin acids

with 5C5 units: Sesterterpenes (C25): Cochliobolin

with 6 C5 units: triterpenes (C30): steroids, sterols, squalene, cardiac glycosides like digitoxin

with 8 C5 units:tetraterpenes (C40): carotenoids

with > 40 C5 units: Polyterpenes (>C200): Rubber

General information
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Dimethylallyl pyrophosphate (DMAPP) and its isomer, isopentenyl pyrophosphate (IPP), are a central component in the biosynthesis of terpenes. Both contain 5 carbon atoms and one double bond. They are also known as "activated isoprene". The biosynthetic pathway starts from acetyl-CoA as the original building block, which is converted to mevalonic acid. From the mevalonic acid the building blocks dimethyl allyl pyrophosphate (DMAPP) and its isomer isopentyl pyrophosphate (IPP) are then synthesized.

The enzyme farnesyl pyrophosphate synthase further catalyzes 1 molecule of dimethyl allyl pyrophosphate and 2 molecules of the isomer isopentyl pyrophosphate to farnesyl pyrophosphate (FPP). Farnesyl pyrophosphate forms the basic framework of the cytosolic sesquiterpenes (seqi - greek=one and a half). Squalene, the basic skeleton of the triterpenes, is formed from 2 units of farnesyl phosphate by means of the squalene synthase.

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Most terpenes are of rare animal origin. They are a main component of the essential oils produced by plants (cosmetic, allergological and naturopathic significance). - see below aromatherapy). Terpenes are used in the cosmetic industry as odorants or flavorings in perfumes and cosmetic products.

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Today only hydrocarbons are counted as terpenes, whereas all oxygenated isoprene derivatives are called terpenoids. In addition, names have become established for terpenes, which are often derived from the name of the plant from which they were first isolated (e.g. citronellol from citronell grass, geraniol-geranium extract, rose furan as a component of rose oil, pinene as a component of pine (pinus), etc.)

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