Terpene

Information about Terpene

Terpenes are a large and varied class of hydrocarbons, produced primarily by a wide variety of plants, particularly conifers, though also by some insects such as swallowtail butterflies, which emit terpenes from their osmeterium. They are the major components of resin, and of turpentine produced from resin. The name "terpene" is derived from the word "turpentine".

When terpenes are modified chemically, such as by oxidation or rearrangement of the carbon skeleton, the resulting compounds are generally referred to as terpenoids. Some authors will use the term terpene to include all terpenoids.

Terpenes and terpenoids are the primary constituents of the essential oils of many types of plants and flowers. Essential oils are used widely as natural flavor additives for food, as fragrances in perfumery, and in traditional and alternative medicines such as aromatherapy. Synthetic variations and derivatives of natural terpenes and terpenoids also greatly expand the variety of aromas used in perfumery and flavors used in food additives. Vitamin A is an example of a terpene.

Structure and biosynthesis

Terpenes are derived biosynthetically from units of isoprene, which has the molecular formula C₅H₈. The basic molecular formulas of terpenes are multiples of that, (C₅H₈)_n where n is the number of linked isoprene units. This is called the isoprene rule or the C5 rule. The isoprene units may be linked together "head to tail" to form linear chains or they may be arranged to form rings. One can consider the isoprene unit as one of nature's common building blocks.

Isoprene itself does not undergo the building process, but rather activated forms, isopentenyl pyrophosphate (IPP or also isopentenyl diphosphate) and dimethylallyl pyrophosphate (DMAPP or also dimethylallyl diphosphate), are the components in the biosynthetic pathway. IPP is formed from acetyl-CoA via the intermediacy of mevalonic acid in the HMG-CoA reductase pathway. An alternative, totally 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.

Dimethylallyl pyrophosphate

Isopentenyl pyrophosphate

As chains of isoprene units are built up, the resulting terpenes are classified sequentially by size as hemiterpenes, monoterpenes, sesquiterpenes, diterpenes, sesterterpenes, triterpenes, and tetraterpenes.

Types

Second or third instar caterpillar of Papilio glaucus emit terpenes from their osmeterium

Hemiterpenes consist of a single isoprene unit. Isoprene itself is considered the only hemiterpene, but oxygen-containing derivatives such as prenol and isovaleric acid are hemiterpenoids.
Monoterpenes consist of two isoprene units and have the molecular formula C₁₀H₁₆. Examples of monoterpenes are: geraniol, limonene and terpineol.
Sesquiterpenes consist of three isoprene units and have the molecular formula C₁₅H₂₄. Examples of sesquiterpenes are: farnesol. The sesqui- prefix means one and a half.
Diterpenes are composed for four isoprene units and have the molecular formula C₂₀H₃₂. They derive from geranylgeranyl pyrophosphate. Examples of diterpenes are cafestol, kahweol, cembrene and taxadiene (precursor of taxol). Diterpenes also form the basis for biologically important compounds such as retinol, retinal, and phytol.
Sesterterpenes, terpenes having 25 carbons and five isoprene units, are rare relative to the other sizes. The sester- prefix means half to three, i.e. two and a half.
Triterpenes consist of six isoprene units and have the molecular formula C₃₀H₄₈. The linear triterpene squalene, the major constituent of shark liver oil, is derived from the reductive coupling of two molecules of farnesyl pyrophosphate. Squalene is then processed biosynthetically to generate either lanosterol or cycloartenol, the structural precursors to all the steroids.
Tetraterpenes contain eight isoprene units and have the molecular formula C₄₀H₅₆. Biologically important tetraterpenes include the acyclic lycopene, the monocyclic gamma-carotene, and the bicyclic alpha- and beta-carotenes.
Polyterpenes consist of long chains of many isoprene units. Natural rubber consists of polyisoprene in which the double bonds are cis. Some plants produce a polyisoprene with trans double bonds, known as gutta-percha.

Agri-chemical use

Research into terpenes has found that many of them possess qualities that make them ideal active ingredients as part of natural agricultural pesticides.

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hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. With relation to chemical terminology, aromatic hydrocarbons or arenes, alkanes, alkenes and alkyne-based compounds composed entirely of carbon or hydrogen are referred to as "Pure" hydrocarbons, whereas
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Pinophyta

Class: Pinopsida

Orders & Families

Cordaitales †
Pinales
  Pinaceae - Pine family
  Araucariaceae - Araucaria family
  Podocarpaceae - Yellow-wood family
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osmeterium is a fleshy organ found in the prothoracic segment of larvae (caterpillars) of Swallowtail butterflies including Birdwings. This organ emits smelly compounds believed to be pheromones.
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Resin or Rosin (Oxford dictionary) is a hydrocarbon secretion of many plants, particularly coniferous trees, valued for its chemical constituents and uses such as varnishes, adhesives, as an important source of raw materials for organic synthesis, or for incense and
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Turpentine (also called spirit of turpentine, oil of turpentine, wood turpentine, gum turpentine) is a fluid obtained by the distillation of resin obtained from trees, mainly pine trees. It is composed of terpenes, mainly the monoterpenes alpha-pinene and beta-pinene.
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terpenoids, sometimes referred to as 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.
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essential oil is any concentrated, hydrophobic liquid containing volatile aroma compounds from plants, which are called aromatic herbs or aromatic plants. They are also known as volatile or ethereal
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Aromatherapy is a form of alternative medicine that uses volatile liquid plant materials, known as essential oils (EOs), and other scented compounds from plants for the purpose of affecting a person's mood or health.
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Vitamin A is an essential human nutrient. It exists not as a single compound, but in several forms. In foods of animal origin, the major form of vitamin A is an alcohol (retinol), but can also exist as an aldehyde (retinal), or as an acid (retinoic acid).
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Isoprene is a common synonym for the chemical compound 2-methylbuta-1,3-diene. It is commonly used in industry, is an important biological material, and can be a harmful environmental pollutant and toxicant when present in excess quantities.
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Isopentenyl pyrophosphate (IPP) is an intermediate in the classical, HMG-CoA reductase pathway used by organisms in the biosynthesis of terpenes and terpenoids. IPP is formed from acetyl-CoA via mevalonic acid.
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Dimethylallyl pyrophosphate (or -diphosphate) (DMAPP) is an intermediate product of both mevalonic acid (MVA) pathway and DOXP/MEP pathway. It is an isomer of isopentenyl pyrophosphate (IPP) and exists in virtually all life forms.
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Acetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main use is to convey the carbon atoms within the acetyl group to Krebs Cycle to be oxidized for energy production.
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Mevalonic acid is a key organic compound in biochemistry. It is a precursor in the biosynthetic pathway, known as the HMG-CoA reductase pathway, that produces terpenes and steroids.

Mevalonic acid is very soluble in water and in polar organic solvents.
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The mevalonate pathway or HMG-CoA reductase pathway or mevalonate-dependent (MAD) route, is an important cellular metabolic pathway present in all higher eukaryotes and many bacteria.
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3-Methyl-2-buten-1-ol is a natural alcohol. It is one of the most simple terpenes. It is a clear colorless oil that is insoluble in water, but miscible with most common organic solvents. It has a fruity odor and is used occasionally in perfumery.
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3-Methylbutanoic acid, or more commonly isovaleric acid, is a natural fatty acid found in a wide variety of plants and essential oils. Isovaleric acid is clear colorless liquid that is sparingly soluble in water, but extremely soluble in most common organic solvents.
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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.
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Geraniol, also called rhodinol, is a monoterpenoid and an alcohol. It is the primary part of oil-of-rose, palmarosa oil, and citronella oil (Java type). It also occurs in small quantities in geranium, lemon, and many other essential oils.
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Limonene is a hydrocarbon, classed as a terpene. It is a colourless liquid at room temperatures with an extremely strong smell of oranges. It takes its name from the lemon, as the rind of the lemon, like other citrus fruits, contains considerable amounts of this chemical compound,
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Terpineol is a naturally occurring monoterpene alcohol that has been isolated from a variety of sources such as cajuput oil, pine oil, and petitgrain oil ^[1].
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Sesquiterpenes are a class of terpenes that consist of three isoprene units and have the molecular formula C₁₅H₂₄. Like monoterpenes, sesquiterpenes may be acyclic or contain rings, including many unique combinations.
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Farnesol is a natural organic compound which is a sesquiterpene alcohol found as a colorless liquid. It is insoluble in water, but miscible with oils.

It is present in many essential oils such as citronella, neroli, cyclamen, lemon grass, tuberose, rose, musk, balsam
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Geranylgeranyl pyrophosphate is an intermediate in the HMG-CoA reductase pathway used by organisms in the biosynthesis of terpenes and terpenoids. In plants it is additionally the precursor to carotenoids, gibberellins, tocopherols, and chlorophyls.
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Cafestol is a diterpene molecule present in coffee.

A typical bean of Coffea arabica contains about 0.6% cafestol by weight. Cafestol is present in highest quantity in unfiltered coffee drinks such as French press coffee or Turkish coffee.
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Cembrene, or sometimes neocembrene, is a natural monocyclic diterpene. It is a colorless oil with a faint wax-like odor.

Cembrene itself has little importance as chemical entity, being a trail pheromone for termites; however, the chemical structure of cembrene is
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