Monoterpene

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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]

Contents

Biosynthesis

Monoterpenes are derived biosynthetically from units of isopentenyl pyrophosphate, which is formed from acetyl-CoA via the intermediacy of mevalonic acid in the 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 barks, heartwood, bark and leaves of coniferous trees, in vegetables, fruits and herbs. [5] Essential oils are very rich in monoterpenes. Several monoterpenes produced by trees, such as linalool, hinokitiol, and ocimene have fungicidal and 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, sabinene contributes to the spicy taste of black pepper, 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 floor cleaners with certain monoterpenes may cause indoor air pollution equivalent or exceeding the harm to respiratory tracts when the time is spent near a busy road. This is due to ozonolysis of monoterpenes like Limonene leading to the production of atmospheric SOA. [20] [21] Another study suggests monoterpenes substantially affect ambient organic aerosol with uncertainties regarding environmental impacts. [22] In a review, scientists concluded that they hope that these "substances will be extensively studied and used in more and more in medicine". [23] A 2013 study found that "Based on adverse effects and risk assessments, d-limonene may be regarded as a safe ingredient. However, the potential occurrence of skin irritation necessitates regulation of this chemical as an ingredient in cosmetics." [24] [ 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

Related Research Articles

The terpenoids, also known as isoprenoids, are a class of naturally occurring organic chemicals derived from the 5-carbon compound isoprene and its derivatives called terpenes, diterpenes, etc. While sometimes used interchangeably with "terpenes", terpenoids contain additional functional groups, usually containing oxygen. When combined with the hydrocarbon terpenes, terpenoids comprise about 80,000 compounds. They are the largest class of plant secondary metabolites, representing about 60% of known natural products. Many terpenoids have substantial pharmacological bioactivity and are therefore of interest to medicinal chemists.

<span class="mw-page-title-main">Terpene</span> Class of oily organic compounds found in plants

Terpenes are a class of natural products consisting of compounds with the formula (C5H8)n for n ≥ 2. Terpenes are major biosynthetic building blocks. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plants, particularly conifers. In plants, terpenes and terpenoids are important mediators of ecological interactions, while some insects use some terpenes as a form of defense. Other functions of terpenoids include cell growth modulation and plant elongation, light harvesting and photoprotection, and membrane permeability and fluidity control.

<span class="mw-page-title-main">Menthol</span> Organic compound used as flavouring and analgesic

Menthol is an organic compound, more specifically a monoterpenoid, made synthetically or obtained from the oils of corn mint, peppermint, or other mints. It is a waxy, clear or white crystalline substance, which is solid at room temperature and melts slightly above.

<span class="mw-page-title-main">Geraniol</span> Monoterpenoid and alcohol that is the primary component of citronella oil

Geraniol is a monoterpenoid and an alcohol. It is the primary component of citronella oil and is a primary component of rose oil and palmarosa oil. It is a colorless oil, although commercial samples can appear yellow. It has low solubility in water, but it is soluble in common organic solvents. The functional group derived from geraniol is called geranyl.

Diterpenes are a class of terpenes composed of four isoprene units, often with the molecular formula C20H32. They are biosynthesized by plants, animals and fungi via the HMG-CoA reductase pathway, with geranylgeranyl pyrophosphate being a primary intermediate. Diterpenes form the basis for biologically important compounds such as retinol, retinal, and phytol. They are known to be antimicrobial and anti-inflammatory.

<span class="mw-page-title-main">Linalool</span> Chemical compound with a floral aroma

Linalool refers to two enantiomers of a naturally occurring terpene alcohol found in many flowers and spice plants. Linalool has multiple commercial applications, the majority of which are based on its pleasant scent. A colorless oil, linalool is classified as an acyclic monoterpenoid. In plants, it is a metabolite, a volatile oil component, an antimicrobial agent, and an aroma compound. Linalool has uses in manufacturing of soaps, fragrances, food additives as flavors, household products, and insecticides. Esters of linalool are referred to as linalyl, e.g. linalyl pyrophosphate, an isomer of geranyl pyrophosphate.

<span class="mw-page-title-main">Limonene</span> Liquid terpene hydrocarbon fragrance and flavor, extract of citrus peel

Limonene is a colorless liquid aliphatic hydrocarbon classified as a cyclic monoterpene, and is the major component in the volatile oil of citrus fruit peels. The (+)-isomer, occurring more commonly in nature as the fragrance of oranges, is a flavoring agent in food manufacturing. It is also used in chemical synthesis as a precursor to carvone and as a renewables-based solvent in cleaning products. The less common (-)-isomer has a piny, turpentine-like odor, and is found in the edible parts of such plants as caraway, dill, and bergamot orange plants.

<span class="mw-page-title-main">Eucalyptol</span> Chemical compound

Eucalyptol is a monoterpenoid colorless liquid, and a bicyclic ether. It has a fresh camphor-like odor and a spicy, cooling taste. It is insoluble in water, but miscible with organic solvents. Eucalyptol makes up about 70–90% of eucalyptus oil. Eucalyptol forms crystalline adducts with hydrohalic acids, o-cresol, resorcinol, and phosphoric acid. Formation of these adducts is useful for purification.

<span class="mw-page-title-main">Myrcene</span> Chemical compound

Myrcene, or β-myrcene, is a monoterpene. A colorless oil, it occurs widely in essential oils. It is produced mainly semi-synthetically from Myrcia, from which it gets its name. It is an intermediate in the production of several fragrances. α-Myrcene is the name for the isomer 2-methyl-6-methylene-1,7-octadiene, which has not been found in nature.

<span class="mw-page-title-main">Nerol</span> Chemical compound

Nerol is a monoterpenoid alcohol found in many essential oils such as lemongrass and hops. It was originally isolated from neroli oil, hence its name. This colourless liquid is used in perfumery. Like geraniol, nerol has a sweet rose odor but it is considered to be fresher. Esters and related derivatives of nerol are referred to as neryl, e.g., neryl acetate.

Camphene is a bicyclic organic compound. It is one of the most pervasive monoterpenes. As with other terpenes, it is insoluble in water, flammable, colorless, and has a pungent smell. It is a minor constituent of many essential oils such as turpentine, cypress oil, camphor oil, citronella oil, neroli, ginger oil, valerian, and mango. It is produced industrially by isomerization of the more common alpha-pinene using a solid acid catalyst such as titanium dioxide.

<span class="mw-page-title-main">Ocimene</span> Chemical compound

Ocimenes are a group of isomeric hydrocarbons. The ocimenes are monoterpenes found within a variety of plants and fruits. α-Ocimene and the two β-ocimenes differ in the position of the isolated double bond: it is terminal in the alpha isomer. α-Ocimene is cis-3,7-dimethyl-1,3,7-octatriene. β-Ocimene is trans-3,7-dimethyl-1,3,6-octatriene. β-Ocimene exists in two stereoisomeric forms, cis and trans, with respect to the central double bond. The ocimenes are often found naturally as mixtures of the various forms. The mixture, as well as the pure compounds, are oils with a pleasant odor. They are used in perfumery for their sweet herbal scent, and are believed to act as plant defense and have anti-fungal properties. Like the related acyclic terpene myrcene, ocimenes are unstable in air. Like other terpenes, the ocimenes are nearly insoluble in water, but soluble in common organic solvents.

<span class="mw-page-title-main">Sesquiterpene</span> Class of terpenes

Sesquiterpenes are a class of terpenes that consist of three isoprene units and often have the molecular formula C15H24. Like monoterpenes, sesquiterpenes may be cyclic or contain rings, including many unique combinations. Biochemical modifications such as oxidation or rearrangement produce the related sesquiterpenoids. A recent study conducted in the Cosmics Leaving Outdoor Droplets large cloud chamber at CERN, has identified sesquiterpenes—gaseous hydrocarbons that are released by plants—as potentially playing a major role in cloud formation in relatively pristine regions of the atmosphere.

<span class="mw-page-title-main">Cannabis flower essential oil</span> Essential oil obtained from the hemp plant

Cannabis flower essential oil, also known as hemp essential oil, is an essential oil obtained by steam distillation from the flowers, panicles, stem, and upper leaves of the hemp plant. Hemp essential oil is distinct from hemp seed oil and hash oil: the former is a vegetable oil that is cold-pressed from the seeds of low-THC varieties of hemp, the latter is a THC-rich extract of dried female hemp flowers (marijuana) or resin (hashish).

<span class="mw-page-title-main">Terpineol</span> Chemical compound

Terpineol is any of four isomeric monoterpenoids. Terpenoids are terpene that are modified by the addition of a functional group, in this case, an alcohol. Terpineols have been isolated from a variety of sources such as cardamom, cajuput oil, pine oil, and petitgrain oil. Four isomers exist: α-, β-, γ-terpineol, and terpinen-4-ol. β- and γ-terpineol differ only by the location of the double bond. Terpineol is usually a mixture of these isomers with α-terpineol as the major constituent.

<span class="mw-page-title-main">Bornyl diphosphate synthase</span>

In enzymology, bornyl diphosphate synthase (BPPS) (EC 5.5.1.8) is an enzyme that catalyzes the chemical reaction

<span class="mw-page-title-main">Terpene synthase N terminal domain</span> Protein domain

In molecular biology, this protein domain belongs to the terpene synthase family (TPS). Its role is to synthesize terpenes, which are part of primary metabolism, such as sterols and carotene, and also part of the secondary metabolism. This entry will focus on the N terminal domain of the TPS protein.

<span class="mw-page-title-main">Terpene synthase C terminal domain</span> Protein domain

In molecular biology, this protein domain belongs to the terpene synthase family (TPS). Its role is to synthesize terpenes, which are part of primary metabolism, such as sterols and carotene, and also part of the secondary metabolism. This entry will focus on the C terminal domain of the TPS protein.

(−)-α-Pinene synthase is an enzyme with systematic name geranyl-diphosphate diphosphate-lyase [cyclizing, (−)-α-pinene-forming]. This enzyme catalyses the following chemical reaction

(−)-β-Pinene synthase (EC 4.2.3.120, β-geraniolene synthase, (−)-(1S,5S)-pinene synthase, geranyldiphosphate diphosphate lyase (pinene forming)) is an enzyme with systematic name geranyl-diphosphate diphosphate-lyase [cyclizing, (−)-β-pinene-forming]. This enzyme catalyses the following chemical reaction

References

  1. ↑ Eberhard Breitmaier (2006). "Hemi‐ and Monoterpenes". Terpenes: Flavors, Fragrances, Pharmaca, Pheromones. pp. 10–23. doi:10.1002/9783527609949.ch2. ISBN   9783527609949.
  2. ↑ Davis, Edward M.; Croteau, Rodney (2000). "Cyclization enzymes in the biosynthesis of monoterpenes, sesquiterpenes, and diterpenes". Topics in Current Chemistry. 209: 53–95. doi:10.1007/3-540-48146-X_2. ISBN   978-3-540-66573-1.
  3. ↑ Brown, R.T. (1975). "Bicyclic Monoterpenoids". Supplements to the 2nd Edition of Rodd's Chemistry of Carbon Compounds: 53–93. doi:10.1016/B978-044453346-3.50098-6. ISBN   9780444533463.
  4. ↑ Vil’, Vera; Yaremenko, Ivan; Ilovaisky, Alexey; Terent’ev, Alexander (2 November 2017). "Peroxides with Anthelmintic, Antiprotozoal, Fungicidal and Antiviral Bioactivity: Properties, Synthesis and Reactions". Molecules. 22 (11): 1881. doi: 10.3390/molecules22111881 . PMC   6150334 . PMID   29099089.
  5. ↑ Sjöström, Eero (22 October 2013). "Chapter 5: Extractives". Wood Chemistry: Fundamentals and Applications (Second ed.). San Diego. ISBN   978-0-08-092589-9.{{cite book}}: CS1 maint: location missing publisher (link)
  6. ↑ Rowell, Roger M. (2013). "Chater 3: Cell Wall Chemistry". Handbook of Wood Chemistry and Wood Composites (2nd ed.). Boca Raton: Taylor & Francis. ISBN   9781439853801.
  7. ↑ D. V. Spracklen; B. Bonn; K. S. Carslaw (2008). "Boreal forests, aerosols and the impacts on clouds and climate" (PDF). Philosophical Transactions of the Royal Society A . 366 (1885): 4613–26. Bibcode:2008RSPTA.366.4613S. doi:10.1098/rsta.2008.0201. PMID   18826917. S2CID   206156442.
  8. ↑ Tamer, Canan Ece; Suna, Senem; Özcan-Sinir, Gülşah (2019). "14 - Toxicological Aspects of Ingredients Used in Nonalcoholic Beverages". Non-alcoholic beverages. Volume 6: The Science of Beverages. Duxford, United Kingdom: Woodhead Publishing. pp. 441–481. doi:10.1016/B978-0-12-815270-6.00014-1. ISBN   978-0-12-815270-6. S2CID   187341441.
  9. ↑ PDR for herbal medicines (4th ed.). Montvale, NJ: Thomson. 2007. p. 802. ISBN   978-1-56363-512-0.
  10. ↑ "Herbs of the Labiatae". Encyclopedia of food sciences and nutrition (2nd ed.). Amsterdam: Academic Press. 2003. pp. 3082–3090. doi:10.1016/B0-12-227055-X/00593-9. ISBN   978-0-12-227055-0.
  11. ↑ Saeidnia, Soodabeh; Gohari, Ahmad Reza (2012). "Trypanocidal Monoterpenes". Studies in Natural Products Chemistry. 37: 173–190. doi:10.1016/B978-0-444-59514-0.00006-7. ISBN   9780444595140.
  12. ↑ Loza-Tavera, Herminia (1999). "Monoterpenes in Essential Oils". Chemicals via Higher Plant Bioengineering. Advances in Experimental Medicine and Biology. Vol. 464. pp. 49–62. doi:10.1007/978-1-4615-4729-7_5. ISBN   978-1-4613-7143-4. PMID   10335385.
  13. ↑ "Limonene". pubchem.ncbi.nlm.nih.gov.
  14. ↑ Laszlo, Pierre (2007). Citrus: A history. Chicago: University of Chicago Press. ISBN   9780226470283.
  15. ↑ Caputi, Lorenzo; Aprea, Eugenio (1 January 2011). "Use of Terpenoids as Natural Flavouring Compounds in Food Industry". Recent Patents on Food, Nutrition & Agriculture. 3 (1): 9–16. doi:10.2174/2212798411103010009. PMID   21114471.
  16. 1 2 Comprehensive natural products chemistry (1st ed.). Amsterdam: Elsevier. 1999. p. 306. ISBN   978-0-08-091283-7.
  17. ↑ "R.E.D. FACTS: Thymol" (PDF). United States Environmental Protection Agency.
  18. ↑ "Camphor Cream and Ointment Information". Drugs.com.
  19. ↑ Tisserand, Robert (2014). "Chapter 13: Essential oil profiles". Essential oil safety : a guide for health care professionals (Second ed.). Edinburgh: Churchill Livingstone. ISBN   978-0-443-06241-4.
  20. ↑ "Cleaning products cause indoor pollution levels similar to a busy road". New Scientist. Retrieved 10 March 2022.
  21. ↑ Rosales, Colleen Marciel F.; Jiang, Jinglin; Lahib, Ahmad; Bottorff, Brandon P.; Reidy, Emily K.; Kumar, Vinay; Tasoglou, Antonios; Huber, Heinz; Dusanter, Sebastien; Tomas, Alexandre; Boor, Brandon E.; Stevens, Philip S. (25 February 2022). "Chemistry and human exposure implications of secondary organic aerosol production from indoor terpene ozonolysis". Science Advances. 8 (8): eabj9156. Bibcode:2022SciA....8J9156R. doi:10.1126/sciadv.abj9156. ISSN   2375-2548. PMC   8880786 . PMID   35213219.
  22. ↑ Zhang, Haofei; Yee, Lindsay D.; Lee, Ben H.; Curtis, Michael P.; Worton, David R.; Isaacman-VanWertz, Gabriel; Offenberg, John H.; Lewandowski, Michael; Kleindienst, Tadeusz E.; Beaver, Melinda R.; Holder, Amara L.; Lonneman, William A.; Docherty, Kenneth S.; Jaoui, Mohammed; Pye, Havala O. T.; Hu, Weiwei; Day, Douglas A.; Campuzano-Jost, Pedro; Jimenez, Jose L.; Guo, Hongyu; Weber, Rodney J.; de Gouw, Joost; Koss, Abigail R.; Edgerton, Eric S.; Brune, William; Mohr, Claudia; Lopez-Hilfiker, Felipe D.; Lutz, Anna; Kreisberg, Nathan M.; Spielman, Steve R.; Hering, Susanne V.; Wilson, Kevin R.; Thornton, Joel A.; Goldstein, Allen H. (12 February 2018). "Monoterpenes are the largest source of summertime organic aerosol in the southeastern United States". Proceedings of the National Academy of Sciences. 115 (9): 2038–2043. Bibcode:2018PNAS..115.2038Z. doi: 10.1073/pnas.1717513115 . ISSN   0027-8424. PMC   5834703 . PMID   29440409.
  23. ↑ Wojtunik‐Kulesza, Karolina A.; Kasprzak, Kamila; Oniszczuk, Tomasz; Oniszczuk, Anna (8 November 2019). "Natural Monoterpenes: Much More than Only a Scent". Chemistry & Biodiversity. 16 (12): e1900434. doi:10.1002/cbdv.201900434. ISSN   1612-1872. PMID   31587473. S2CID   203850556.
  24. ↑ Kim, Young Woo; Kim, Min Ji; Chung, Bu Young; Bang, Du Yeon; Lim, Seong Kwang; Choi, Seul Min; Lim, Duck Soo; Cho, Myung Chan; Yoon, Kyungsil; Kim, Hyung Sik; Kim, Kyu Bong; Kim, You Sun; Kwack, Seung Jun; Lee, Byung-Mu (1 January 2013). "Safety Evaluation And Risk Assessment Of d-Limonene". Journal of Toxicology and Environmental Health, Part B. 16 (1): 17–38. doi:10.1080/10937404.2013.769418. ISSN   1093-7404. PMID   23573938. S2CID   40274650.
  25. ↑ Zárybnický, Tomáš; Boušová, Iva; Ambrož, Martin; Skálová, Lenka (1 January 2018). "Hepatotoxicity of monoterpenes and sesquiterpenes". Archives of Toxicology. 92 (1): 1–13. doi:10.1007/s00204-017-2062-2. ISSN   1432-0738. PMID   28905185. S2CID   22483285.
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