Terpenes (/ˈtɜːrpiːn/) are a large and diverse class of organic
compounds, produced by a variety of plants, particularly conifers,
and by some insects such as termites or swallowtail butterflies, which
emit terpenes from their osmeteria. They often have a strong odor and
may protect the plants that produce them by deterring herbivores and
by attracting predators and parasites of herbivores. The
difference between terpenes and terpenoids is that terpenes are
hydrocarbons, whereas terpenoids contain additional functional groups.
They are the major components of resin, and of turpentine produced
from resin. The name "terpene" is derived from the word "terpentine",
an obsolete form of the word "turpentine". In addition to their roles
as end-products in many organisms, terpenes are also major
biosynthetic building blocks within nearly every living creature.
Steroids, for example, are derivatives of the triterpene squalene.
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. Terpenoids are also known as
Terpenes and terpenoids are the primary constituents of the essential
oils of many types of medicinal plants and flowers. Essential oils are
used widely as fragrances in perfumery, and in medicine 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
Vitamin A is a terpenoid.
Higher amounts of terpenes are released by trees in warmer weather,
acting as a natural form of cloud seeding. The clouds reflect
sunlight, allowing the forest temperature to regulate. The aroma
and flavor of hops comes, in part, from sesquiterpenes (mainly
alpha-humulene and beta-caryophyllene), which affect beer quality.
Terpenes are also major constituents of
Cannabis sativa plants, which
contain at least 120 identified compounds.
1 Structure and biosynthesis
5 External links
Structure and biosynthesis
Terpenes are derived biosynthetically from units of isoprene, which
has the molecular formula C5H8. The basic molecular formula of
terpenes are multiples of that, (C5H8)n where n is the number of
linked isoprene units. This is called the biogenetic isoprene rule or
the C5 rule. In 1953,
Leopold Ružička discovered that 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. As chains of isoprene
units accumulate, the resulting terpenes are classified sequentially
by size as hemiterpenes, monoterpenes, sesquiterpenes, diterpenes,
sesterterpenes, triterpenes, and tetraterpenes, all synthesized by
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.
Second- or third-instar caterpillars of
Papilio glaucus emit terpenes
from their osmeterium.
Terpenes may be classified by the number of isoprene units in the
molecule; a prefix in the name indicates the number of terpene units
needed to assemble the molecule.
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 and monoterpenoids include
geraniol, terpineol (present in lilacs), limonene (present in citrus
fruits), myrcene (present in hops), linalool (present in lavender) or
pinene (present in pine trees).
Iridoids derive from monoterpenes.
Sesquiterpenes consist of three isoprene units and have the molecular
formula C15H24. Examples of sesquiterpenes and sesquiterpenoids
include humulene, farnesenes, farnesol. (The sesqui- prefix means one
and a half.)
Diterpenes are composed of four isoprene units and have the molecular
formula C20H32. They derive from geranylgeranyl pyrophosphate.
Examples of diterpenes and diterpenoids are cafestol, kahweol,
cembrene and taxadiene (precursor of taxol).
Diterpenes also form the
basis for biologically important compounds such as retinol, retinal,
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.) An example of a sesterterpenoid is
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.
Sesquarterpenes are composed of seven isoprene units and have the
molecular formula C35H56. Sesquarterpenes are typically microbial in
their origin. Examples of sesquarterpenoids are ferrugicadiol and
Tetraterpenes contain eight isoprene units and have the molecular
formula C40H64. Biologically important tetraterpenoids 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
Norisoprenoids, such as the C13-norisoprenoids 3-oxo-α-ionol present
Muscat of Alexandria
Muscat of Alexandria leaves and 7,8-dihydroionone derivatives, such
as megastigmane-3,9-diol and 3-oxo-7,8-dihydro-α-ionol found in
Shiraz leaves (both grapes in the species Vitis vinifera) or
wine (responsible for some of the spice notes in Chardonnay),
can be produced by fungal peroxidases or glycosidases.
Terpenes have desirable properties for use in food, cosmetics,
pharmaceutical and biotechnology industries.
The complex structure of many terpenes often makes their chemical
synthesis difficult, and the extraction from plants is also difficult
and time-consuming, and yields only small amounts. The genomes of 17
plant species contain genes that encode terpenoid synthase enzymes
imparting terpenes with their basic structure, and cytochrome P450s
that modify this basic structure.
Terpenes have properties that make them useful active ingredients as
part of natural agricultural pesticides. Terpenes are used by
termites of the
Nasutitermitinae family to ward off predatory insects,
through the use of a specialized mechanism called a fontanellar
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Wikimedia Commons has media related to Terpenes.
Institute of Chemistry - terpenes
Structures of alpha pinene and beta pinene
Terpenes at the US National Library of Medicine Medical Subject
Types of Terpenes and Terpenoids (# of isoprene units)
Acyclic (linear, cis and trans forms)
Monocyclic (single ring)
Bicyclic (2 rings)
Iridoids (cyclopentane ring)
Iridoid glycosides (iridoids bound to a sugar)
Steroids (4 rings)
Pinene (β and α
Cholecalciferol (Vit D)
sap, resins, latex of many plants, e.g. rubber
Terpene synthase enzymes (many), having in common a
Terpene synthase N
terminal domain (protein domain)
Activated isoprene forms
Isopentenyl pyrophosphate (IPP)
Dimethylallyl pyrophosphate (DMAPP)