Secondary metabolites are organic compounds produced by living organisms that are not essential for growth. They are classified into five major groups: polyketides and fatty acids, terpenes and steroids, phenylpropanoids, alkaloids, and specialized amino acids and peptides. Many secondary metabolites have medical applications as antibiotics, analgesics, stimulants, or insecticides. They also serve important ecological roles for organisms such as defense against pathogens or signaling in interactions.

1. CLASSIFICATIONOF SECONDARY
METABOLITESANDTHEIR
APPLICATIONS
BY -
Saurabh Kumar
Research Scholar
Dept. Of Chemistry
D.E.I

2. Introduction
Natural Products
• Natural products are the organic compounds which are formed by the
living systems.
• The term natural product is used to refer compounds produced from
natural sources.
Natural products are classified in two groups –
• Primary metabolites.
• Secondary metabolites.
Metabolite
• An intermediate or end product of metabolism.

3. PrimaryMetabolites
Compounds which occur in all cells and play a central role in the
metabolism and reproduction of those cells.
Examples are - amino acids, proteins, enzymes, sugars, nucleic acids
etc.
Important for the intrinsic functions of the organism.
referred to as central metabolite.
Some common examples of primary metabolites are ethanol, lactic
acid and certain amino acids.

4. SecondaryMetabolites
Secondary metabolites can be defined as a heterogeneous group of natural
metabolic products that are not essential for vegetative growth of the producing
organisms.
They are considered differentiation compounds conferring adaptive roles.
For example, by functioning as defense compounds or signaling molecules in
ecological interactions, symbiosis, metal transport, competition, and so on.
The term “secondary” for such natural compounds was introduced by a. Kossel
in 1891.
Secondary metabolites are derived from primary metabolism.

5. Classificationof secondarymetabolites
Most of these compounds belong to one of several families, each of
which have structural characteristics arising from the way in which they
are built up in nature, i.e. From their biosynthesis.
Based on their biosynthetic origins, secondary metabolites can be divided
in to five major groups :
1. Polyketides and fatty acids
2. Terpenoids and steroids
3. Phenylpropanoids
4. Alkaloids
5. Specialized amino acids and peptides

6. 1. Polyketidesandfattyacids
Polyketides
Natural products that are formed by the stepwise condensation of acetate
(ethanoate) units.
In the resultant carbon chain, alternate carbon atoms come from the methyl
and carboxyl groups of the acetate building blocks which leads to forms
even-numbered carbon chains.
Produced in bacteria, fungi, plants, and certain marine animals.
Some examples are -

7. Fatty acids
• A fatty acid is a carboxylic acid with a long aliphatic chain, which is either saturated or
unsaturated.
• Most naturally occurring fatty acids have an unbranched chain of an even number of
carbon atoms, from 4 to 28.
• Exist as three main classes of esters: triglycerides, phospholipids, and cholesteryl esters.
• In plants the fatty acids and the corresponding alcohols are found in leaf
• Waxes and seed coatings.
• Some common examples are - Myristoleic acid CH3(CH2)3CH=CH(CH2)7COOH
Palmitoleic acid CH3(CH2)5CH=CH(CH2)7COOH
Sapienic acid CH3(CH2)8CH=CH(CH2)4COOH
Oleic acid CH3(CH2)7CH=CH(CH2)7COOH
Elaidic acid CH3(CH2)7CH=CH(CH2)7COOH
Vaccenic acid CH3(CH2)5CH=CH(CH2)9COOH
Linoleic acid CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH

8. Applicationsof Polyketidesandfattyacids
Many polyketides are medicinal or exhibit acute toxicity.
Geldanamycin, a useful antibiotic.
Doxycycline, another important antibiotic.
Erythromycin, an antibiotic.
Aflatoxin is one of the most carcinogenic compounds known.
The arachidonic acid is a precursor of the prostaglandin hormones.
Fatty acids are mainly used in the production of cosmetic and soaps.
Fatty alcohols and fatty amines are precursors to surfactants,
detergents, and lubricants.
Other applications include their use as emulsifiers, texturizing
agents, wetting agents, anti-foam agents, or stabilizing agents.

9. 2. Terpenesand Steroids
Terpenes
• The terpenes are compounds that are built up from isoprene units.
• Their structures are divisible into the c5 isoprene units linked in a head-to-tail manner.
• Produced by a variety of plants, particularly conifers, and by some insects.
• Often have a strong odor.
• The simplest terpene is a pair of isoprenes with formula c10h16. One such simple terpene is pinene, a
component of cannabis extracts with a pine forest scent.
Examples -

10. Steroids
• A steroid is a biologically active organic compound with four rings arranged in a specific molecular
configuration.
• The steroid core structure is typically composed of seventeen carbon atoms, bonded in four
"fused" rings: three six-member cyclohexane and one five-member cyclopentane ring .
• Steroids vary by the functional groups attached to this four-ring core and by the oxidation state of
the rings.
• Sterols are forms of steroids with a hydroxy group at position three and a skeleton derived from
cholestane.
• Hundreds of steroids are found in plants, animals and fungi.
• Examples -

11. Applicationsof Terpenesand Steroids
• Terpenes are useful natural agricultural pesticides.
• Higher amounts of terpenes are released by trees in warmer weather and may be a
natural form of cloud seeding.
• The provitamin beta carotene is a terpene derivative called a carotenoid.
• Terpenes are also major constituents of cannabis sativa plants, which contain at least
120 identified compounds.
• Similar to lipids, steroids are highly concentrated energy stores. However, they are not
typically sources of energy; in mammals, they are normally metabolized and excreted.
• Steroids play critical roles in several disorders, including malignancies like prostate
cancer.

12. 3. Phenylpropanoids
• The phenylpropanoids are a diverse family of organic
compounds that are synthesized by plants from the
amino acids phenylalanine and tyrosine.
• Some of these compounds are associated with the
photosensitizing properties of plants of the
umbelliferae.
• Phenylpropanoids are found throughout the plant
kingdom.
• They serve as essential components of several
structural polymers, provide protection from
ultraviolet light, defend against herbivores and
pathogens.
• Oxidative coupling of two phenylpropanoid units,
such as coniferyl alcohol leads to the lignan carbon
skeleton.
• Podophyllotoxin from the hindu drug podophylium
emodi (himalayan mayapple), is an interesting
cytotoxic agent.
• Some examples are -

13. Applications
• Hydroxycinnamic acids produces
some of the volatile components of
herb and flower fragrances, which
serve many functions such as
attracting pollinators.
• The phenylpropenes, including
eugenol, chavicol, safrole and
estragole, are the primary
constituents of various essential
oils.
• Coumarins and flavonoids are the
diverse class of phytochemicals.

14. 4. Alkaloids
• Alkaloids are a class of basic, naturally occurring organic compounds that contain at least
one nitrogen atom.
• This group also includes some related compounds with neutral and even weakly acidic
properties.
• Some synthetic compounds of similar structure may also be termed alkaloids
• In addition to carbon, hydrogen and nitrogen, alkaloids may also contain oxygen, sulfur
and, more rarely, other elements such as chlorine, bromine, and phosphorus.
• Alkaloids are produced by a large variety of organisms including bacteria, fungi, plants,
and animals.
• Some examples are -

15. Applications
• Many alkaloids are used in medicine, usually in the form of salts widely used including
the following –
• Some alkaloids, such as salts of nicotine and anabasine, were used as insecticides.
Their use was limited by their high toxicity to humans.
• Cocaine, caffeine, and cathinone are stimulants of the central nervous system.
• Mescaline and many indole alkaloids (psilocybin, dimethyltryptamine) have
hallucinogenic effect.
• Morphine and codeine are strong narcotic pain killers.
Alkaloid Action
Ajmaline antiarrhythmic
Emetine antiprotozoal agent,Emesis
Ergot alkaloids Vasoconstriction, hallucinogenic, Uterotonic
Morphine analgesic
Nicotine stimulant, nicotinic acetylcholine receptor agonist
Physostigmine inhibitor of acetylcholinesterase

16. 5. Specializedaminoacidsandpeptides
• The amino acids are the building blocks for peptides and
proteins.
• Although the amino acids are normally considered as
primary metabolites, there are some unusual amino
acids that are of restricted occurrence.
• Some antibiotics such as the penicillins and
cephalosporins are formed from small peptides.
• The diketopiperazine antifungal agents produced by
Trichoderma and Gliocladium species, such as gliotoxin
are also derived from amino acids.