Introduction to terpene

2. All terpenoids are biosynthesized from just
two C5 precursors: isopentyl pyrophosphate
(IPP) and dimethylallyl diphosphate
(DMAPP).
The biosynthesis of terpenoids can
divided into three main steps:
1. Biosynthesis of active isoprene units IPP
and DMAPP.
2. Condensation of this units to form acyclic
terpenoids.
Terpenoids Biosynthesis

3. 1. Biosynthesis of IPP and
DMAPP units
The two universal terpene precursors,
IPP and DMAPP are biosynthesized via
two pathways:
A. Acetate-mevalonate (Ac-MVA)
pathway.
(Assignment )

4. +
OPP
OPP
–
+
OPP
OPP
Formation of acyclic terpenoids
The double bond of isopentenyl
pyrophosphate acting as a nucleophile
toward the allylic carbon of dimethylallyl
pyrophosphate.
2. Condensation of
isoprene units

5.  After C—C bond formation, the carbocation can lose a
proton to give a double bond to form geranyl
pyrophosphate (GPP, C10) leading to the formation of
the monoterpenoids.
 Condensation of GPP with an IPP leads to the
formation of farnesyl pyrophosphate (FPP, C15), the
precursor of sesquiterpenoids.
 Farnesyl pyrophosphate is extended by another
isoprene unit by reaction with isopentenyl
pyrophosphate to form geranylgeranyl pyrophosphate
(GGPP, C20), the precursor of diterpenoids.
 GGPP+IPP leads to the formation of sesterpenoids.
 Dimerization of two FPP gives rise to squalene,
which is the precursor of triterpenoids and indirectly,

6. Formation of acyclic

7. 3. Cyclization and introduction of
functional groups
 The families of enzymes responsible for the formation
of terpenoids from GPP, FPP, and GGPP are known
as monoterpene, sesquiterpene, and diterpene
synthases, respectively.
 Terpenoid synthases that produce cyclic products are
also referred to as “cyclases”.
Formation of cyclic monoterpenes

8. Hemiterpenes C5H8
Hemiterpenes represent the simplest terpenes
class, containing a single isoprene unit.
These compounds can be found in different plant
parts.
The best known hemiterpene is isoprene itself, a
volatile product released from photosynthetically
active tissues.
Isoprene is most readily available industrially as a
byproduct of the thermal cracking of naphtha or oil,
as a side product in the production of ethylene.
About 95% of isoprene production is used to

9. Oxygenated Hemiterpenes
Prenol
It is a natural alcohol. It is a clear
colorless oil. It has a fruity odor and is
used occasionally in perfumery.
It occurs in citrus fruits, grapes, tomato,
coffee and others.

10. Isovaleric acid
A fatty acid with a pungent taste and
disagreeable odor that is found in:
• Valerian and other plant products, as well
as in cheese.
• The sweat of feet
• As a metabolite of the amino acid leucine
and is found in
the urine of patients with smallpox,
hepatitis, and typhus.

11. Monoterpenoids C10H16
Approximately 1500 monoterpenes are
documented.
Monoterpenoids have been isolated
from the fragrant oils of many plants
and are important in the perfumery and
flavour industries.
Monoterpenoids are also found in many

12. 1
2
3
4
5
6
7
8
9
10
2,6- dimethyloctane
Acyclic monoterpenoids
They are formed by a head to tail
arrangement of the isoprene units.
They are principally found in plants
and in insect exudates.
They can regarded as derivatives of
the saturated hydrocarbon, 2,6-
dimethyloctane.

13. Monocyclic Monoterpenes
• Monocyclic terpenes are derivedfrom
the cis-trans-
isomers of p-menthane.
• Trans-p-menthane itself occurs in the
oil of turpentine.
• Its o- and m-isomers are rarely
occurring.

14. Bicyclic monoterpene hydrocarbons
may be regarded as derived from:
1. p-menthane by direct union of two C
atoms and the formation of simple
bridge (Carbonium ion
rearrangement).
2. Methylated cyclohexane by bridging
with CH2 or (CH3)2.
Bicyclic Monoterpenes

15. Bicyclic Monoterpenes
Carane and thujane, camphane,
isocamphane and fenchane are the most
important skeletons of naturally occurring
bicyclic monoterpenes.

16. Sesquiterpenes (C15H24)
Sesquiterpenoids (b.p.250-280 oC), from
the precursor farnesyl pyrophosphate,
are found mainly in higher plants, and
also in some invertebrates.
Classification
I) Acyclic sesquiterpenoids
2) Monocyclic
3) Bicyclic
4) Tricyclic