• The
terpenoids are
a class of natural products which have been derived from five-carbon
isoprene
units.
• Most
of
the terpenoids have
multi
cyclic
structures that differ from one another by their functional groups and basic carbon
skeletons.
• These
types
of natural lipids can
be
found in every class of living things, and therefore considered as the largest group of natural
products.
• Many
of
the terpenoids are commercially
interesting
because of their use as flavours
and
fragrances in
foods and cosmetics examples
menthol
and sclareol
or
because they are
important
for the quality of agricultural products,
such as the flavour of
fruits and the fragrance of
flowers like linalool.
• Terpenes
are widespread
in nature, mainly in plants as constituents of essential
oils.
• Their
building
block
is
the hydrocarbon isoprene, CH2=C(CH3)-CH=CH2.
•Terpene
hydrocarbons
therefore
have
molecular formula (C5H8) n and they are classified
according to the number of isoprene units.
1 Hemiterpenoids:
Consist
of a single isoprene
unit.
The only hemiterpene is the Isoprene itself, but oxygen-containing derivatives
of
isoprene such as isovaleric acid
and prenol is
classify as hemiterpenoids.
2 Monoterpenoids:
Biochemical
modifications
of
monoterpenes such as oxidation
or
rearrangement produce the related monoterpenoids. Monoterpenoids have
two isoprene
units.
Monoterpenes may be of two types i.e linear (acyclic) or contain rings e.g.
•Geranyl pyrophosphate, Eucalyptol, Limonene,
•Citral, Camphor and Pinene.
3 Sesquiterpenes: Sesquiterpenes have three isoprene units e.g. Artemisinin, Bisabolol and Fernesol, oil of flowers, or as cyclic compounds, such as Eudesmol, found in Eucalyptus oil.
4 Diterpenes: It composed for four isoprene units. They derive from geranylgeranyl pyrophosphate. There are some examples of diterpenes such as cembrene, kahweol, taxadiene and cafestol. Retinol, retinal, and phytol are the biologically important compounds while using diterpenes as the base.
5 Triterpenes: It consists of six isoprene units e.g. Lanosterol and squalene found in wheat germ, and olives.
6 Tetraterpenoids: It contains eight isoprene units which may be acyclic like lycopene, monocyclic like gamma-carotene, and bicyclic like alpha- and betacarotenes.
Activity of Terpenes
• Among plant secondary metabolites terpenoids are a structurally most diverse group; they function as phytoalexins in plant direct defense, or as signals in indirect defense responses which involves herbivores and their natural enemies.
• Many plants produce volatile terpenes in order to attract specific insects for pollination or otherwise to expel certain animals using these plants as food.
• Less volatile but strongly bitter-tasting or toxic terpenes also protect some plants from being eaten by animals (antifeedants).
•Geranyl pyrophosphate, Eucalyptol, Limonene,
•Citral, Camphor and Pinene.
3 Sesquiterpenes: Sesquiterpenes have three isoprene units e.g. Artemisinin, Bisabolol and Fernesol, oil of flowers, or as cyclic compounds, such as Eudesmol, found in Eucalyptus oil.
4 Diterpenes: It composed for four isoprene units. They derive from geranylgeranyl pyrophosphate. There are some examples of diterpenes such as cembrene, kahweol, taxadiene and cafestol. Retinol, retinal, and phytol are the biologically important compounds while using diterpenes as the base.
5 Triterpenes: It consists of six isoprene units e.g. Lanosterol and squalene found in wheat germ, and olives.
6 Tetraterpenoids: It contains eight isoprene units which may be acyclic like lycopene, monocyclic like gamma-carotene, and bicyclic like alpha- and betacarotenes.
Activity of Terpenes
• Among plant secondary metabolites terpenoids are a structurally most diverse group; they function as phytoalexins in plant direct defense, or as signals in indirect defense responses which involves herbivores and their natural enemies.
• Many plants produce volatile terpenes in order to attract specific insects for pollination or otherwise to expel certain animals using these plants as food.
• Less volatile but strongly bitter-tasting or toxic terpenes also protect some plants from being eaten by animals (antifeedants).
•Last, but
not least,
terpenes play an important role as signal compounds and growth regulators (phytohormones)
of
plants, as shown by preliminary
investigations.
In addition, terpenoids can have
medicinal properties such as anti-carcinogenic (e.g.
perilla
alcohol), antimalarial (e.g. artemisinin), anti-ulcer, hepaticidal,
antimicrobial
or
diuretic (e.g. glycyrrhizin) activity and
the sesquiterpenoid
antimalarial drug artimisinin
and
the diterpenoid
anticancer drug taxol.
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