about terpenoids

1. A presentation on
terpenoids
PRESENTATION BY
ARUNKUMAR K R
MSC THIRD SEMESTER
DEPARTMENT OF PHARMACEUTICAL CHEMISTRY

2. Index
 Introduction
 Classification
 Occurence
 Isolation of terpenoids
 Structural elucidation of Menthol
 Synthesis of Menthol
 Biological important of terpenoids
 Conclusion
 References

3. Introduction
 TERPENOIDS:
Terpenoids are defined as the hydrocarbons of plant origin having the general formula-
(C5H8)n Where n is the number of linked isoprene ( 2-methyl-1,3-butadiene) units
(isoprenoids). Terpenoids can be thought of as modified terpenes. However the term terpene
is misnomer and restricted to the hydrocarbons C10H16 as the suffix “ene” signifes unsaturated
hydrocarbons and so the term terpene is in appropriate to compound having aldehydes.
Ketones & alcohol functionality i.e., terpenoids.
 OCCURRENCE:
Terpenoids form a group of compounds, the majority of which occurs in plant kingdom.
 Mono and sesquiterpenoids are the essential oils obtained from sap and tissues of plants
and trees.
 Di and Tri Terpenoids are obtained from plant and tree gums and resins.
 Tetra terpenoids form a group of compounds known as carotenoids.
 Polyterpenoids: Rubber.

4. CLASSIFICATION OF TERPENOIDS
 Most natural terpenoids hydrocarbon have the general formula (C5H8)n. They can be classified
on the basis of value of ‘n’ i.e., isoprene unit or number of carbon atoms present in the structure.
Class No. of isoprene units (C5H8) Molecular formulae
1.Hemiterpene or isoprene 1 C5H8
2.Monoterpenes or Terpene 2 C10H18
3.Sesquiterpenes 3 C15H24
4.Diterpenes 4 C20H32
5.Triterpenes 6 C30H48
6.Tetraterpenes or Carotenoids 8 C40H64
7.Polyterpenes or Rubber n (C5H8)n

5. Each class can be further subdivided into subclass according to the number of rings present in
the structure:
I ) Acyclic Terpenoids: They contain open structure. E.g., Citral
ii) Monocyclic Terpenoids: They contain one ring in the structure. E.g., Menthol
iii) Bicyclic Terpenoids: They contain two rings in the structure.E.g., Camphor
iv) Tricyclic Terpenoids: They contain three rings in the structure. E.g.,Abietic acid
v) Tetracyclic Terpenoids: They contain four rings in the structure. Expand. E.g.,gibberellic acid

6. Isolation of terpenoids
I ) Isolation of essential from plant parts
 a) Expression method
 b) Steam distillation
 c) Extraction by means of volatile solvents
 d) Adsorption in purified fats/Enfluerage
ii) Separation of terpenoids from essential oils
 a) Chemical method
 b) Physical method

7. I) CHEMICAL METHOD:
 Essential oils containing terpenoid hydrocarbon + nitrosyl chloride in chloroform form crystalline
adduct of hydrocarbons.
 Essential oil containing alcohols

9. Menthol
 Occurrence: Obtained from peppermint or other mint oils
 Crystalline substance, clear or white in colour, which is solid at room temperature and melts
slightly above (43°c).

10. Structural elucidation of Menthol
1. Molecular formula: C10H20O
2. Menthol forms esters readily with it means that it possess an alcoholic group.
Menthol then oxidizes to yield ketone, menthol (C10H18O) it indicates that the alcoholic group is
secondary in nature.
C10H20O [O] C10H18O
Menthol Menthone
3.On dehydration followed by dehydrogenation it yields p- cymene. It indicates presence of
p-cymene skeleton (p-menthane skeleton) in two compounds.
Menthol

11.  4.Menthone on oxidation with KMnO4 yields ketoacid C10H18O3.
It possess one keto group and one carboxyl group and is called ketomenthylic acid.
 It readily oxidized to 3-methyladipic acid. These reactions can be explained by considering the
following structure of menthol.

12.  Menthol was converted to p-cymene [1-methyl-4-isopropylbenzene], which was also obtained by
dehydrogenation of pulegone.
 Pulegone on reduction yields menthone which on further reduction gives menthol.

13. Synthesis
 Finally the structure of menthone and menthol have been confirmed by the synthesis given
by Kotz and Hese from m-cresol.

14. Biological importance of Terpenoids
Plant terpenoids are used extensively for their aromatic qualities. They play a
role in traditional herbal remedies and are under investigation for
antibacterial, antineoplastic, and other pharmaceutical functions.

15. Conclusion
 From this presentation i conclude that

16. References
 “Organic chemistry of natural products” ; volume 2; GURDEEP R
CHATWAL;
page no: 1.1-1.155
 “Organic chemistry of natural products” volume 1;O.P AGARWAL;
page no:312-433