Monoterpene

Source: Wikipedia, the free encyclopedia.

Monoterpenes are a class of terpenes that consist of two isoprene units and have the molecular formula C10H16. Monoterpenes may be linear (acyclic) or contain rings (monocyclic and bicyclic). Modified terpenes, such as those containing oxygen functionality or missing a methyl group, are called monoterpenoids. Monoterpenes and monoterpenoids are diverse. They have relevance to the pharmaceutical, cosmetic, agricultural, and food industries.[1]

Biosynthesis

Main article: Terpene § Biosynthesis

Monoterpenes are derived biosynthetically from units of

HMG-CoA reductase pathway. An alternative, unrelated biosynthesis pathway of IPP is known in some bacterial groups and the plastids of plants, the so-called MEP-(2-methyl-D-erythritol-4-phosphate) pathway, which is initiated from C5 sugars
. In both pathways, IPP is isomerized to DMAPP by the enzyme isopentenyl pyrophosphate isomerase.

Geranyl pyrophosphate is the precursor to monoterpenes (and hence monoterpenoids).[2] Elimination of the pyrophosphate group from geranyl pyrophosphate leads to the formation of acyclic monoterpenes such as ocimene and the myrcenes. Hydrolysis of the phosphate groups leads to the prototypical acyclic monoterpenoid geraniol. Additional rearrangements and oxidations provide compounds such as citral, citronellal, citronellol, linalool, and many others. Many monoterpenes found in marine organisms are halogenated, such as halomon.

Main examples

Bicyclic monoterpenes include

carene, sabinene, camphene, and thujene. Camphor, borneol, eucalyptol and ascaridole are examples of bicyclic monoterpenoids containing ketone, alcohol, ether, and bridging peroxide functional groups, respectively.[3][4] Umbellulone
is another example of bicyclic monoterpene ketone.

Natural roles

Monoterpenes are found in many parts of different plants, such as

antibacterial activities and participate in wound healing.[6] Some of these compounds are produced to protect the trees from insect
attacks.

Monoterpenes are emitted by forests and form aerosols that are proposed to serve as cloud condensation nuclei (CCN). Such aerosols can increase the brightness of clouds and cool the climate.[7]

Many monoterpenes have unique smell and flavor. For example,

3-carene gives cannabis an earthy taste and smell, citral has a lemon-like pleasant odor and contributes to the distinctive smell of citrus fruits, and thujene and carvacrol are responsible for the pungent flavors of summer savory and oregano, respectively.[8][9][10]

Monoterpenes are considered allelochemicals.[11]

Uses

Many monoterpenes are volatile compounds and some of them are well-known fragrants found in the essential oils of many plants.[12] For example, camphor, citral, citronellol, geraniol, grapefruit mercaptan, eucalyptol, ocimene, myrcene, limonene, linalool, menthol, camphene and pinenes are used in perfumes and cosmetic products. Limonene and perillyl alcohol are used in cleaning products.[13][14]

Many monoterpenes are used as food flavors and food additives, such as bornyl acetate, citral, eucalyptol, menthol, hinokitiol, camphene and limonene.[15][16] Menthol, hinokitiol and thymol are also used in oral hygiene products. Thymol also has antiseptic and disinfectant properties.[17]

Volatile monoterpenes produced by plants can attract or repel insects, thus some of them are used in insect repellents, such as citronellol, eucalyptol, limonene, linalool, hinokitiol, menthol and thymol.[16]

Ascaridole, camphor and eucalyptol are monoterpenes that have pharmaceutical use.[18][19]

Health effects

A study suggests that a range of

better source needed] According to a review, several studies showed "that some monoterpenes (e.g., pulegone, menthofuran, camphor, and limonene) and sesquiterpenes (e.g., zederone, germacrone) exhibited liver toxicity" and that i.a. intensive research on terpenes toxicity is needed.[25]

See also

References

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  8. S2CID 187341441
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  13. ^ "Limonene". pubchem.ncbi.nlm.nih.gov.
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  15. PMID 21114471
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  16. ^
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  17. ^ "R.E.D. FACTS: Thymol" (PDF). United States Environmental Protection Agency.
  18. ^ "Camphor Cream and Ointment Information". Drugs.com.
  19. ISBN 978-0-443-06241-4
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  20. ^ "Cleaning products cause indoor pollution levels similar to a busy road". New Scientist. Retrieved 10 March 2022.
  21. PMID 35213219
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  23. S2CID 203850556
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  24. S2CID 40274650
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  25. S2CID 22483285
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