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Chemical structure of the terpenoid isopentenyl pyrophosphate, an intermediate in the HMG-CoA reductase pathway

The terpenoids (/ˈtɜːrpɪnɔɪd/ TUR-pin-oyd), sometimes called isoprenoids, are a large and diverse class of naturally occurring organic chemicals similar to terpenes, derived from five-carbon isoprene units assembled and modified in thousands of ways. Most are multicyclic structures that differ from one another not only in functional groups but also in their basic carbon skeletons, these lipids can be found in all classes of living things, and are the largest group of natural products. About 60% of known natural products are terpenoids.[1]

Plant terpenoids are used extensively for their aromatic qualities and play a role in traditional herbal remedies. Terpenoids contribute to the scent of eucalyptus, the flavors of cinnamon, cloves, and ginger, the yellow color in sunflowers, and the red color in tomatoes.[2] Well-known terpenoids include citral, menthol, camphor, salvinorin A in the plant Salvia divinorum, the cannabinoids found in cannabis, ginkgolide and bilobalide found in Ginkgo biloba, and the curcuminoids found in turmeric and mustard seed.

The steroids and sterols in animals are biologically produced from terpenoid precursors. Sometimes terpenoids are added to proteins, e.g., to enhance their attachment to the cell membrane; this is known as isoprenylation.

Structure and classification[edit]

Terpenes are hydrocarbons resulting from the condensation of several 5-carbon isoprene units. The isoprene unit has the formula CH2=C(CH3)CH=CH2. Terpenoids can be thought of as modified terpenes, wherein methyl groups have been moved or removed, or oxygen atoms added. (Some authors use the term "terpene" more broadly, to include the terpenoids.) Just like terpenes, the terpenoids can be classified according to the number of isoprene units used:

Terpenoids can also be classified according to the number of cyclic structures they contain, the Salkowski test can be used to identify the presence of terpenoids.[3]

Meroterpenes are any compound, including many natural products, having a partial terpenoid structure.


Simplified version of the steroid synthesis pathway with the terpenoid intermediates isopentenyl pyrophosphate (IPP), dimethylallyl pyrophosphate (DMAPP), geranyl pyrophosphate (GPP), and squalene shown. Some intermediates are omitted for clarity.

There are two metabolic pathways that create terpenoids:

Mevalonic acid pathway[edit]

Many organisms manufacture terpenoids through the HMG-CoA reductase pathway, which also produces cholesterol, the reactions take place in the cytosol. The pathway was discovered in the 1950s.

MEP/DOXP pathway[edit]

The 2-C-methyl-D-erythritol 4-phosphate/1-deoxy-D-xylulose 5-phosphate pathway (MEP/DOXP pathway), also known as [non-mevalonate pathway] or mevalonic acid-independent pathway, takes place in the plastids of plants and apicomplexan protozoa, as well as in many bacteria. It was discovered in the late 1980s.

Pyruvate and glyceraldehyde 3-phosphate are converted by DOXP synthase (Dxs) to 1-deoxy-D-xylulose 5-phosphate, and by DOXP reductase (Dxr, IspC) to 2-C-methyl-D-erythritol 4-phosphate (MEP). The subsequent three reaction steps catalyzed by 4-diphosphocytidyl-2-C-methyl-D-erythritol synthase (YgbP, IspD), 4-diphosphocytidyl-2-C-methyl-D-erythritol kinase (YchB, IspE), and 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase (YgbB, IspF) mediate the formation of 2-C-methyl-D-erythritol 2,4-cyclopyrophosphate (MEcPP). Finally, MEcPP is converted to (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMB-PP) by HMB-PP synthase (GcpE, IspG), and HMB-PP is converted to isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP) by HMB-PP reductase (LytB, IspH).

IPP and DMAPP are the end-products in either pathway, and are the precursors of isoprene, monoterpenoids (10-carbon), diterpenoids (20-carbon), carotenoids (40-carbon), chlorophylls, and plastoquinone-9 (45-carbon). Synthesis of all higher terpenoids proceeds via formation of geranyl pyrophosphate (GPP), farnesyl pyrophosphate (FPP), and geranylgeranyl pyrophosphate (GGPP).

Although both pathways, MVA and MEP, are mutually exclusive in most organisms, interactions between them have been reported in plants and few bacteria species.[citation needed]

Organism Pathways
Bacteria MVA or MEP
Archaea MVA
Green Algae MEP
Plants MVA and MEP
Animals MVA
Fungi MVA



Monoterpenoids are the largest group of secondary metabolites in plants,[4] these 10 carbon-atom compounds present large diversity and have relevance to the pharmaceutical, cosmetic, agricultural and food industries.[5] Additionally, monoterpenes can be used as gasoline additives and their dimerization may generate second order fuel molecules, suitable as supplements for diesel type fuels. Monoterpenes are usually volatile compounds, due to their relatively low molecular weights. Mostly used in perfumes, it is a starting material for synthesis of vitamin 'A'.


Sesquiterpenes are isoprenoid molecules with 15 carbon atoms, they are formed via the condensation of one IPP unit to geranyl-pyrophosphate (GPP), originating farnesyl-pyrophosphate (FPP). The FPP backbone can be rearranged in several different ways and further decorated with different functional groups, hence the large variety of sesquiterpenoids.[6] Geosmin, the volatile compound that gives an earthy taste and musty odor in drinking water and the characteristic odor on a rainy day, is a sesquiterpenoid, produced by bacteria, especially cyanobacteria, that are present in the soils and water supplies. [7]


Diterpenes are structurally diverse hydrocarbons with 20 carbon atoms, derived from the addition of one IPP unit to FPP to form geranylgeranyl-pyrophosphate (GGPP), from GGPP, structural diversity is achieved mainly by two classes of enzymes: the diterpene synthases and cytocromes P450. The chemical synthesis of these compounds is typically difficult and their availability in nature is quite limited due to the laborious work required for their isolation. Several diterpenes are produced by plants and cyanobacteria. GGPP is also the precursor for the synthesis of the phytane by te action of the enzyme geranylgeranyl reductase, this compound is used in plants and cyanobacteria for the biosynthesis of tocopherols and the phytyl functional group is used in the formation of chlorophyll a, ubiquinones, plastoquinone and phylloquinone.[8]


Triterpenes are C30-hydrocarbons, synthesized through the head-to-head condensation of two FPP units to form squalene; in turn, squalene serves as precursor for the formation of triterpenoids, including bacterial hopanoids and eukaryotic sterols. Squalene is itself a valuable compound since it is used as antioxidant, was well as in cosmetics, nutrition and vaccines and it is extracted from shark liver oil or olive or other plan oils. [9][10][11]


Tetraterpenes are C40-hydrocarbons derived from phytoene, which is synthesized via the head-to-head condensation of two GGPP molecules. [12] One group of tetraterpenes, and possibly the most studied one, is the carotenoids pigments. Carotenoids have important biological functions, with roles in light capture, antioxidative activity and protection against free radicals, synthesis of plant hormones and as structural components of the membranes. Aside their biological relevance, carotenoids are also high-value compounds for the food and pharmaceutical industries. Carotenoids are sinthesized by photosynthetic and non-photosynthetic organisms; however, in photosynthetic organisms, they are essential components as accessory pigments for the light-harvesting reaction centers. [13][14][15]

See also[edit]


  1. ^ Firn R (2010). Nature's Chemicals. Oxford: Biology. 
  2. ^ Specter M (September 28, 2009). "A Life of Its Own". The New Yorker. 
  3. ^ Ayoola GA (2008). "Phytochemical Screening and Antioxidant Activities of Some Selected Medicinal Plants Used for Malaria Therapy in Southwestern Nigeria". Tropical Journal of Pharmaceutical Research. 7 (3): 1019–1024. doi:10.4314/tjpr.v7i3.14686. 
  4. ^ Banthorpe DV, Charlwood BV, Francis MJ (April 1972). "Biosynthesis of monoterpenes". Chemical Reviews. 72 (2): 115–155. doi:10.1021/cr60276a002. 
  5. ^ Schewe H, Mirata MA, Holtmann D, Schrader J (October 2011). "Biooxidation of monoterpenes with bacterial monooxygenases". Process Biochemistry. 46 (10): 1885–1899. doi:10.1016/j.procbio.2011.06.010. 
  6. ^ Chizzola R (2013), "Regular Monoterpenes and Sesquiterpenes (Essential Oils)", Natural Products, Springer Berlin Heidelberg, pp. 2973–3008, doi:10.1007/978-3-642-22144-6_130, ISBN 9783642221439 
  7. ^ Izaguirre G, Taylor WD (June 1995). "Geosmin and 2-methylisoborneol production in a major aqueduct system". Water Science and Technology. 31 (11): 41–48. doi:10.1016/0273-1223(95)00454-u. 
  8. ^ Pattanaik B, Lindberg P (January 2015). "Terpenoids and their biosynthesis in cyanobacteria". Life. 5 (1): 269–93. doi:10.3390/life5010269. PMC 4390852Freely accessible. PMID 25615610. 
  9. ^ Huang ZR, Lin YK, Fang JY (January 2009). "Biological and pharmacological activities of squalene and related compounds: potential uses in cosmetic dermatology". Molecules. 14 (1): 540–54. doi:10.3390/molecules14010540. PMID 19169201. 
  10. ^ Fox CB (September 2009). "Squalene emulsions for parenteral vaccine and drug delivery". Molecules. 14 (9): 3286–312. doi:10.3390/molecules14093286. PMID 19783926. 
  11. ^ Güneş FE (2013). "Medical use of squalene as a natural antioxidant". Journal of Marmara University Institute of Health Sciences: 1. doi:10.5455/musbed.20131213100404. 
  12. ^ Umeno D, Tobias AV, Arnold FH (December 2002). "Evolution of the C30 carotenoid synthase CrtM for function in a C40 pathway". Journal of Bacteriology. 184 (23): 6690–9. doi:10.1128/JB.184.23.6690-6699.2002. PMC 135437Freely accessible. PMID 12426357. 
  13. ^ Domonkos I, Kis M, Gombos Z, Ughy B (October 2013). "Carotenoids, versatile components of oxygenic photosynthesis". Progress in Lipid Research. 52 (4): 539–61. doi:10.1016/j.plipres.2013.07.001. PMID 23896007. 
  14. ^ Havaux M (April 1998). "Carotenoids as membrane stabilizers in chloroplasts". Trends in Plant Science. 3 (4): 147–151. doi:10.1016/s1360-1385(98)01200-x. 
  15. ^ Sozer O, Komenda J, Ughy B, Domonkos I, Laczkó-Dobos H, Malec P, Gombos Z, Kis M (May 2010). "Involvement of carotenoids in the synthesis and assembly of protein subunits of photosynthetic reaction centers of Synechocystis sp. PCC 6803". Plant & Cell Physiology. 51 (5): 823–35. doi:10.1093/pcp/pcq031. PMID 20231245. 

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