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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
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.

Contents

1 Structure and classification 2 Biosynthesis

2.1 Mevalonic acid
Mevalonic acid
pathway 2.2 MEP/DOXP pathway

3 Uses

3.1 Monoterpenoids

4 See also 5 References 6 External links

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:

Hemiterpenoids, 1 isoprene unit (5 carbons) Monoterpenoids, 2 isoprene units (10C) Sesquiterpenoids, 3 isoprene units (15C) Diterpenoids, 4 isoprene units (20C) (e.g. ginkgolides) Sesterterpenoids, 5 isoprene units (25C) Triterpenoids, 6 isoprene units (30C) (e.g. sterols) Tetraterpenoids, 8 isoprene units (40C) (e.g. carotenoids) Polyterpenoid
Polyterpenoid
with a larger number of isoprene units

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. Biosynthesis[edit]

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
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
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
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

Uses[edit] Monoterpenoids[edit] Mostly used in perfumes. It is a starting material for synthesis of vitamin 'A'. See also[edit]

List of antioxidants in food List of phytochemicals in food Nutrition Phytochemistry Secondary metabolites

References[edit]

^ Firn, Richard (2010). Nature's Chemicals. Oxford: Biology.  ^ Michael Specter (September 28, 2009). "A Life of Its Own". The New Yorker.  ^ Ayoola, GA (2008). "Phytochemical Screening and Antioxidant Activities of Some Selected Medicinal Plants
Plants
Used for Malaria Therapy in Southwestern Nigeria". Tropical Journal of Pharmaceutical Research. 7 (3): 1019–1024. doi:10.4314/tjpr.v7i3.14686. 

External links[edit]

IUPAC nomenclature of terpenoids

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Secondary metabolites

General

 

Alkaloids

Codeine Morphine Cocaine Tetrodotoxin Atropine

Natural phenols

Polyphenols

Monoterpenoids

Geranyl diphosphate Limonene Pinene

Diterpenoids

Geranylgeranyl diphosphate Taxol Aphidicolin Pimaradiene

Antibiotics

Penicillin Streptomycin Tetracycline

←Enzyme cofactors

 

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Types of Terpenes and Terpenoids (# of isoprene units)

Basic forms:

Acyclic (linear, cis and trans forms) Monocyclic (single ring) Bicyclic (2 rings) Iridoids (cyclopentane ring) Iridoid
Iridoid
glycosides (iridoids bound to a sugar) Steroids (4 rings)

Hemiterpenoids (1)

Isoprene
Isoprene
(C5H8) Prenol Isovaleric acid

Monoterpene
Monoterpene
(C10H16)(2)

Acyclic

Ocimene Myrcenes

Monocyclic

Limonene Terpinene Phellandrene Umbellulone

Bicyclic

Pinene
Pinene
(β and α Camphene Thujene Sabinene Carene

Monoterpenoids (2,modified)

Acyclic

Linalool Citronellal Citral Citronellol Geraniol Geranyl pyrophosphate

Monocyclic

Grapefruit mercaptan menthol p-Cymene thymol Perillyl alcohol Carvacrol

Bicyclic

Camphor Borneol Eucalyptol Halomon Eucalyptol Pinene Ascaridole

Sesquiterpenoids
Sesquiterpenoids
(3)

Farnesyl pyrophosphate Artemisinin Bisabolol

Diterpenoids (4)

Geranylgeranyl pyrophosphate Gibberellin Retinol Retinal Phytol Taxol Forskolin Aphidicolin Salvinorin A

Sesterterpenoids (5)

geranylfarnesol

Triterpenoids (6)

Steroids

Phytosterols

Campesterol beta Sitosterol gamma sitosterol Stigmasterol

Tocopherols Cholesterol Testosterone Cholecalciferol
Cholecalciferol
(Vit D) Ecdysones

Other

Saponins Squalane Lanosterol Acids

Oleanolic acid Ursolic acid Betulinic acid Moronic acid

Sesquarterpenes/oids (7)

ferrugicadiol tetraprenylcurcumene

Tetraterpenoids (Carotenoids) (8)

Carotenes

Alpha-Carotene Beta-Carotene Gamma-Carotene Delta-Carotene Lycopene Neurosporene Phytofluene Phytoene

Xanthophylls:

Canthaxanthin Cryptoxanthin Zeaxanthin Astaxanthin Lutein Rubixanthin

Polyterpenoids (many)

sap, resins, latex of many plants, e.g. rubber

Norisoprenoids (modified)

3-oxo-α-ionol 7,8-dihydroionone

Synthesis

Terpene
Terpene
synthase enzymes (many), having in common a Terpene
Terpene
synthase N terminal domain (protein domain)

Activated isoprene forms

Isopentenyl pyrophosphate
Isopentenyl pyrophosphate
(IPP) Dimethylallyl pyrophosp

.