Terpenoids are a class of naturally occurring organic chemicals derived from five-carbon isoprene units. They are produced mainly by plants and play roles such as contributing fragrances to flowers and flavors to fruits. The document discusses the definition, classification, occurrence, biosynthesis, and chemistry of terpenoids. It notes that terpenoids are classified based on the number of isoprene units they contain and can range from simple hemiterpenes to more complex polyterpenes. Their biosynthesis occurs primarily via the mevalonate and non-mevalonate pathways which link isoprene units together.

2. TERPENOIDS
CONTENT
Introduction
Definition
Isoprene rule
Classification
Occurrence
Nomenclature
Biogenetic pathway

3. Introduction
 There are many different classes of naturally occurring
compounds.
 Terpenoids also form a group of naturally occurring
compounds majority of which occur in plants, a few of
them have also been obtained from other sources.
 Terpenoids are volatile substances which give plants &
flowers their fragrance.
 They occur widely in the leaves & fruits of higher plants,
citrus & eucalyptus.

4.  TERPENES are hydrocarbons & component of
resins & also turpentine produced from resin
 Word terpenes is derived from turpentine
 When terpenes are modified chemically such
as by oxidation or rearrangement of carbon
skeleton , the resulting compounds are known
as terpenoids.

5.  Definition: “Terpenoids are the hydrocarbons
of plant origin of the general formula (C5H8)n
as well as their oxygenated, hydrogenated &
dehydrogenated derivatives.”
 Terpenoids are regarded as derivatives of
polymers of isoprene , H2C=C-CH=CH2 (i.e.
C5H8)
CH3

6.  They consist of a complex mixture of
Terpenes or sesquiterpenes,
Alcohols,
Aldehydes,
Ketone,
Acids & esters

7.  Isoprene rule:
States that isoprene units are joined in the
terpenoids via ‘head to tail’ fashion.
 But this rule can only be used as guiding
principle & not as fixed rule.
 E.g Carotenoids are joined tail to tail at their
central.
 Thermal decomposition of terpenoids give
isoprene as one of the product

8. Isoprene
 Isoprene is the common name for
2-methylbuta-1,3-diene
CH2
C CH
CH2CH3
CH2 C CH CH2
CH3
One isoprene unit contains five carbon atoms

9. The Isoprene Rule

10.  Classification of Terpenoids
Most natural terpenoid hydrocarbon have the
general formula (C5H8)n.
They can be classified on the basis of value of
n or no. of carbon atoms present in the
structure.

11. Classification of Terpenoid

12.  Hemiterpenes consist of a single isoprene unit.
Isoprene itself is considered the only hemiterpene
• Monoterpenes consist of two isoprene units & have
the molecular formula C10H16.
• Sesquiterpenes consist of three isoprene units & have
the molecular formula C15H24.
• Diterpenes are composed for four isoprene units &
have the molecular formula C20H32.
Diterpenes also form the basis for biologically
important compounds such as retinol, retinal

13. • Sesterterpenes, terpenes having 25 carbons & 5
isoprene units, are rare relative to the other sizes
• Triterpenes consist of 6 isoprene units & have the
molecular formula C30H48.
• Tetraterpenes contain 8 isoprene units & have the
molecular formula C40H64.
• 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,

14.  Each class can be further subdivided into subclasses according
to the no. of rings present in the structure.
 i) Acyclic Terpenoids: They contain open
structure.
 ii) Monocyclic Terpenoids: They contain 1 ring
in the structure.
 iii) Bicyclic Terpenoids: They contain 2 rings in
the structure.
 iv) Tricyclic Terpenoids: They contain 3 rings in
the structure.
 v) Tetracyclic Terpenoids: They contain 4 rings
in the structure.

20.  Distribution & occurrence
 Widely distributed in certain plant families (rich)…e.g., Pinaceae,
Lauraceae, Rutaceae, Myrtaceae, UmbelIiferae, Labiatae and
Compositae.
 Depending on the plant family……………..Occur in specialized
secretory structure.
 Glandular hairs (Labiatae).
 Modified parenchyma cells (Piperaceae).
 Oil-ducts called vittae (Umbelliferae).
 Lysigenous or schizogenous passages (Pinacease, Rutaceae).
 Formation: Directly……..…by the protoplasm.
 Decomposition of the resinogenous layer of the cells wall.
 or by Hydrolysis of ………...certain gIycosides.

21. Occurrence
 Ocurres in……………………… All tissues.
 Rose………………….Petals.
 Cinnamon…………….Bark and the leaves.
 Umbelliferous fruits…..Pericarp.
 Mints…………………Glandular hairs of the stems&leaves.
 Orange….. ……...1. Flower petals. 2. The rind.

22. Monoterpenes : They are the terpenes that have been
known for several centuries as components of the
fragrant oils obtained from leaves, flowers & fruits
Monoterpenes, with sesquiterpenes, are the main
constituents of essential oils which is found in
Higher plants
While a few, such as camphor, occur in a near pure form,
most occur as complex mixtures

23.  They are found in Gymnosperm,
Angiosperm(flowering plants) &
concentrated in the families like Lamiaceae,
 Umbelliferae,
 Myrtaceae, Rutaceae ,
 Santalaceae,
 Zingiberaceae.

24. DITERPENES
They are of fungal or plant origin and are found in
resins, gummy exudates,
usually co-occur with mono- & sequiterpenoids but
rarely with triterpenoids
Commonly present resins & trees of Leguminosae,
Burseraceae, Lamiaceae, Euphorbiaceae, Solanaceae &
Meliaceae

25.  Sesterpenoids
 Rarely found
 Found in protective waxes of insects & fungi
 They are phytotoxic
 Triterpenoids
 Commonly found in Leguminosae, Cucurbitaceae,
Meliaceae, Apocynaceae, Moraceae
 Found in any part of plant as free or glycosidic form

26.  Tetraterpenoids : (carotenoids)
 They are found in non-photosynthesis of plant tissues,
in fungi & bacteria
 Due its long chain of conjugated double bonds, the
carotenoids are colored yellow, orange & red
 Occurs in many plants & distributed in almost all parts
of the plant such as root(carrot), leaves (spinach), fruits
(tomato), seeds( annatto)

27.  Terpenes & terpenoids are found in all volatile oils,
resins & resins combinations of plant or animal origin
 Drug containing terpenoids are known as
terpenoidal drug

28. General properties of Terpenoids
 Most of the terpenoids are colourless, fragrant liquids which are
lighter than water & volatile with steam
 A few of them are solids e.g. camphor.
 All are soluble in organic solvent & usually insoluble in water.
 Most of them are optically active.
 They are open chain or cyclic unsaturated compounds having one
or more double bonds.
 Consequently they undergo addition reaction with hydrogen,
halogen, acids, etc. A no. of addition products have antiseptic
properties.

29. They undergo polymerization & dehydrogenation
They are easily oxidized nearly by all the oxidizing
agents. On thermal decomposition.
Most of the terpenoids yields isoprene as one of the
product.

30.  Biogenesis pathway
 The two biosyntheic pathways leading to terpenoids are
-- The Mevalonate pathways- (Mevalonic acid formed from 3
molecules of acetyl-CoA)
-- Mevalonate –independent pathways via 1-deoxy –D-
xylulose -5- phosphate- arises from a combination of two
glycolytic pathway intermediate, namely pyruvic acid and
glyceraldehyde 3-phosphate.

31.  The mevalonate pathway, predominantly used by plants
and in a few insect species
 The non-mevalonate pathway or methyl D-erythritol 4-
phosphate (MEP) pathway, which occurs in plant
chloroplasts, algae, cyanobacteria, eubacteria, and
important pathogens such as Mycobacterium tuberculosis
and malaria parasites

32. Terpenes- Biosynthesis
The Mevalonate-pathways
Mevalonic acid + deoxyxylulose phosphate
Non- Mevalonate
pathways

33. Formation of Geranyl pyrophosphate
Terpene Biosynthesis

35. Formation of Farnesyl Pyrophosphate

36. Formation of Squalene, the Precursor of
Cholesterol

37. Geranyl pyrophosphate C10 Monoterpenes (C10)
Isopentyl pyrophasphate C5
Farnesyl pyrophosphate Sesquiterpens (C15)
C15 (units)
Isoprenyl pyrophosphate Diterpenes
C20 Tetraterpens
C 30
Polyterpens
Squalene
Triterpenes

38. Chemistry of volatile oils
 Chemical examination of the volatile oils has shown that they
consist of a complex mixtures of compounds, acyclic, alicyclic,
aromatic & heterocyclic.
 These constituents may be classified broadly into
 i) Terpenes, related to isoprene or isopentene unit (C5H8).
 ii) Aromatic compound (i.e. derivatives of benzene), e.g.
eugenol, the constituent of oil of cloves.
 iii) Nitrogen-& sulphur-containing compounds e.g.
isothiocyanate, found in mustard oil.
 iv) Miscellaneous compounds, including unbranched, long
chain compounds.

39.  The naturally occurring, unsaturated condensation
products of two isoprene molecules are called terpene
and may be either aliphatic or aromatic in nature.
 The aliphatic terpenes may be hydrocarbons, alcohols,
aldehydes, or ketones….etc.

40. Nomenclature
 The position of the double bond in the structure of the
terpene is indicated by the Greek letterΔ (delta) to
which an index number is attached referring to the first
carbon atom of the doubly linked pair.
 The parent compound for nomenclature is called, P-
menthane, if the compound contains one double bond
it is called, P-menthene, 2 double bonds called, P-
menthadiene.

42.  Δ 1,5 indicates that the double bonds are between 1 & 2
& between 5 & Hydrocarbons of the terpene type are more
common in volatile oils and are classified as foIlows: