TERPENOIDS classification isolation isoprene rule Sajna.pdf

Terpenoids: A Comprehensive OverviewTerpenoids form a significant class of naturally occurring compounds, predominantly found in plants, with a few isolated from other sources as well1. They are volatile substances responsible for giving plants and flowers their characteristic fragrance2. These compounds are widely distributed, notably in the leaves and fruits of higher plants, as well as in conifers, citrus, and eucalyptus3. Historically, the term 'terpene' was first applied to compounds isolated from turpentine, a volatile liquid derived from pine trees4. Chemically, terpenoids are defined as hydrocarbons of plant origin that fit the general formula $(\text{C}_5\text{H}_8)_n$, along with their oxygenated, hydrogenated, and dehydrogenated derivatives5555. Examples of essential natural products that are terpenoids include Geraniol, Farnesol, Ginkgolide, Squalene, beta-carotene, and natural rubber666666666.ClassificationThe classification of terpenoids is primarily based on the value of n, or the number of isoprene units ($\text{C}_5\text{H}_8$) that constitute the molecule7. Terpenoids are grouped as follows: Monoterpenoids ($\text{C}_{10}\text{H}_{16}$) are formed from two isoprene units ($n=2$)8; Sesquiterpenoids ($\text{C}_{15}\text{H}_{24}$) from three ($n=3$)9; Diterpenoids ($\text{C}_{20}\text{H}_{32}$) from four ($n=4$)10; Sesterpenoids ($\text{C}_{25}\text{H}_{40}$) from five ($n=5$)11; Triterpenoids ($\text{C}_{30}\text{H}_{48}$) from six ($n=6$)12; Tetraterpenoids ($\text{C}_{40}\text{H}_{64}$) from eight ($n=8$) 13; and Polyterpenoids ($(\text{C}_5\text{H}_8)_n$) from more than eight ($n>8$) isoprene units14. Each of these classes is further subdivided based on the number of rings present in the structure15. This includes Acyclic Terpenoids, which have an open chain structure16161616; Monocyclic Terpenoids, containing one ring17171717; Bicyclic Terpenoids, containing two rings18181818; Tricyclic Terpenoids, containing three rings 19191919; and Tetracyclic Terpenoids, containing four rings20202020. Examples of Monoterpenoids include acyclic forms like Myrcene, Citral, and Geraniol 21; monocyclic forms such as Limonene, $\alpha$-Terpineol, and Menthol 22; and bicyclic forms like camphor, $\alpha$-pinene, and Bornane23232323. Sesquiterpenoids include acyclic Farnesol 24, monocyclic Zinziberene 25, and bicyclic Cadinene26. Diterpenoids include the acyclic Phytol 27and monocyclic Vitamin A (Retinol)28.Isolation ProceduresBoth mono- and sesquiterpenoids are commonly isolated from essential oils29. The isolation process is typically carried out in two steps: first, the extraction of essential oils from plant parts, and second, the separation of terpenoids from the essential oils using physical and chemical methods30. For extraction, plant material is collected at a time when the essential oil concentration is highest, for example, collecting jasmine at sunset31. Extraction methods include the Expression method.Isoprene rule is also discussed

1. TERPENOIDS
SAJNA K S
1
ST
SEMM.PHARM
DEPARTMENT OFPHARMACEUTICAL CHEMISTRY
ST. JAMES COLLEGE OF PHARMACEUTICAL
SCIENCES

2. Contents
1.Introduction
2.Classification
3.Isolation
4.Isoprene rule
5.Reference

3. INTRODUCTION
•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 and flowers their fragrance.
•They occur widely in the leaves and fruits
of higher plants, conifers, citrus and
eucalyptus.

4. TERPENOIDS
•The term ‘terpene’ was given to the compounds
isolated from terpentine,a volatile liquid isolated from
pine trees.
•“Terpenoids are the hydrocarbons of plant origin of
the general formula (C5H8)n as well as their
oxygenated, hydrogenated and dehydrogenated
derivatives.”

5. CLASSIFICATION
•Most natural terpenoidhydrocarbon have the general formula
(C5H8)n. They can be classified on the basis of value of n or number
of carbon atoms present in the structure.

6. CLASSIFICATION
•Each class can be further subdivided into subclasses according to the number of rings
present in the structure.
TERPENOIDS
Acyclic
Terpenoids
They contain
open
structure
Monocyclic
Terpenoids
They contain
one ring in the
structure
Bicyclic
Terpenoids
They contain
two rings in
the structure
Tricyclic
Terpenoids
They contain
three rings in
the structure
Tetracyclic
Terpenoids
They contain
four rings in
the structure.

7. CLASSIFICATION
•Some examples of mono, sesqiand du terpenoids

8. •ii)Bicyclic monoterpenoids: These are further divided into three classes.
BICYCLIC
MONOTERPENOIDS
Containing -6+3-
membered rings
Containing -6+4-
membered rings
Containing -6+5-
membered rings

10. CLASSIFICATION

11. ISOLATION
•Both mono and sesquiterpenoidshave
common source i.eessential oils. Their
isolation is carried out in two steps.
Step 1
•Extraction of essential oils from
plant parts
Step 2
•Separation of essential oils from
terpenoids
•Physical method
•Chemical method

12. ISOLATION
•Isolation of essential oils from plant parts: The plants having essential oils generally
have the highest concentration at some particular time. Thereforebetter yield of
essential oil plant material have to be collected at this particular time. E.g. From jasmine
at sunset.
Extraction
Expression
method
Steam
distillation
method
Extraction by
means of
volatile solvent
Adsorption in
purified fats

13. ISOLATION
1.Expression method

14. ISOLATION
2. Steam distillation method
Steam distillation uses a combination of gentle pressure and steam to extract terpenes
without breaking down their structures. Essentially, the process involves using vapor
pressure to pull out the terpenes and separate them from other components in the plant.

15. ISOLATION

16. ISOLATION
3.Adsorption in purified fats (Enfleurage)
In this method fat is
warmed on a glass
plate and the surface
of the fat is covered
with flower petals.
It is kept for several
days until it becomes
saturated with
essential oil.
After that petals
are removed and
the fat is digested
with ethyl alcohol.

17. Seperation of terpenoids from essential oils
Separation of terpenoids from essential oils
Chemical methods
METHOD 1
•Essential oil containing terpenoid
hydrocarbons are treated with nitrosyl
chloride in chloroform, crystalline adducts
of hydrocarbons having sharp melting
points are obtained.
METHOD 2
•Essential oil containing alcohols are treated
with phthalic anhydride to form diesters,
after extracting with sodium bicarbonate
diesters are decomposed by alkali to the
parent terpenoid alcohols

18. 3. Method 3
.
Chemical method
ESSENTIAL
OILS
NaHSO3, 2,4-
dinitrophenylhydra
zine,
phenylhydrazine,
semicarbazide
ADDUCT
SEPERATED
DECOMPOSED
TERPENOIDS

19. Physical methods
•1. Fractional distillation
•
Terpenoid hydrocarbon distil over first followed by
oxygenated derivatives
It is carried out under reduced pressure and in presence
of inert gas
Distillation of residue under reduced pressure yields the
sesquiterpenoids and these are separated by fractional
distillation
These conditions are essential because many terpenes
are sensitive to heat and atmospheric oxygen

20. Physical methods
1. Chromatography
Essential oils is made to flow
through particular adsorbent
•ADSORPTION
CHROMATOGRAPHY
Different types of terpenoids
are adsorbed at different
places on the adsorbent to
form different chromatograms
Chromatograms are eluted by
different solvent systems to get
different eluates

21. ISOPRENE RULE
•Thermal decomposition of terpenoids give isoprene as
one of the product
•Isoprene rule stats that the terpenoid molecules are
constructed from two or more isoprene unit.

22. •Ingold suggested that isoprene units are joined in the terpenoid via ‘head to tail’
fashion. Special isoprene rule states that the terpenoid molecule are constructed of
two or more isoprene units joined in a ‘head to tail’ fashion.
Special isoprene rule

23. Isoprene rule
•In applying isoprene rule we look only for the skeletal unit of carbon. The carbon
skeletons of open chain monotrpenoids and sesqui terpenoids are

24. Myrcene
Limonene
Retinol

25. REFERENCE
1.Ludwiczuk A, Skalicka-Woźniak K, Georgiev MI.
Terpenoids. Pharmacognosy. 2017:233-266.
2.Ruzicka L. The isoprene rule and the biogenesis of terpenic
compounds. Experientia. 1953;9(10):357-367.
3.Kolekar SM, Jain BU, Kondawarkar MS. A review on
steroids and terpenoids (stereochemistry, structural
elucidation, isolation of steroids and terpenoids). Res J
Pharm Dosage Forms Technol. 2019;11(2):126-130.
4.Finar IL. Organic Chemistry. Vol. 2. 6th edition, Pearson
education; 2006 , 212-234
5. Bruice PY. Organic Chemistry. 3rd edition, pearson
education; 2010 ;567-584
6. Morrison RT, Boyd RN. Organic Chemistry. 6th edition.
Pearson education; 2009 ,1223-1348
7.Bhat SV, Nagasampagi BA, Kumar MS. Chemistry of
Natural Products. Springer publishers, 2003; 321-352

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