Secondary Metabolites from Plants

Secondary Metabolites from Plants PHARMACEUTICAL BIOTECHNOLOGY

Plant Secondary Metabolites

Secondary metabolites are those metabolites which are often produced in a phase of subsequent to growth, have no function in growth (although they may have survival function), are produced by certain restricted taxonomic groups of microorganisms, have unusual chemicals structures, and are often formed as mixtures of closely related members of a chemical family.

The simplest definition of secondary products is that they are not generally included in standard metabolic charts.


A metabolic intermediate or product, found as a differentiation product in restricted taxonomic groups, not essential to growth and the life of the producing organism, and biosynthesis from one or more general metabolites by a wider variety of pathways than is available in general metabolism.

Secondary metabolites are not essential for growth and tend to be strain specific. They have a wide range of chemical structures and biological activities. They are derived by unique biosynthetic pathways from primary metabolites and intermediates.


Biochemical pathways that are not necessary for growth or reproduction of an organism, but which can be demonstrated genetically, physiologically or biochemically.


Plants produce as amazing diversity of low molecular weight compounds.

Of the estimated 400,000 – 500,000 plant species around the globe, only a small percentage has been investigated phytochemically and the fraction subjected to biological or pharmacological screening is even lower.


The ability to synthesize secondary metabolites has been selected through the course of evolution in different plant lineage when such compounds address specific needs.

Floral scent volatiles and pigments have evolved to attract insect pollinators and thus enhance fertilization.

To synthesize toxic chemical has evolved to ward off pathogens and herbivores or to suppress the growth of neighboring plants.


Chemicals found in fruits prevent spoilage and act as signals (in the form of color, aroma, and flavor) of the presence of potential rewards (sugars, vitamins and flavor) for animals that eat the fruit and thereby help to disperse the seeds.

Other chemicals serve cellular functions that are unique to the particular plant in which they occur (e.g. resistance to salt or drought).

Natural Products Drug Discovery and Development

Natural Products Drug Discovery and Development Over the ages, human have relied on nature

fro their basic needs for the production of foodstuffs, shelters, clothing, means of transportations, fertilizers, flavors and fragrances, and not least medicine.

Plants have formed the basis of sophisticated traditional medicine system that have been in existence thousands of years in countries such as China and India.

Natural Products Drug Discovery and Development About 25% of all prescriptions sold in the US are for

natural products, while another 25% are for structural modifications of a natural products.

According to Fransworth (1990) claims that 119 characterized drugs are still obtained commercially from higher plants and that 74% were found from ethnobotanical information.

Fransworth, N.R. (1990) In bioactive compounds from plants.

John and Wiley Co..

Primary and Secondary Metabolism

Primary and Secondary MetabolismPrimary metabolism

The biological reactions are essential to maintain life in living organisms and are known as primary metabolism.

Plant convert sunlight energy to chemical energy, such as ATP, NADPH, by the mediation of chlorophyll in chloroplasts and synthesize sugars and starch from CO2 by using ATP and NADPH+.

These carbohydrates are stored and used for differentiation and formation of plant tissues.


Secondary metabolismThe metabolisms which are not directly related to maintaining

life, are known as secondary metabolisms.The products formed by secondary metabolism are called

secondary metabolites.Secondary metabolite play a role in reinforcement of tissue and

tree body (e.g. cellulose, lignin, suberin), protection against

insects, dieses, and plant regulation (plant hormones).


All organisms need to transform and interconvert a vast number of organic compounds to enable them to live, grow and reproduce.

All organisms need to provide themselves with energy in the form of ATP, and a supply of building blocks to construct their own tissues.

An integrated network of enzyme-mediated and carefully regulated chemical reactions in used for this purpose, collectively referred to as intermediary metabolism, and the pathways involved are termed metabolic pathway.


The pathways for generally modifying and synthesizing carbohydrates, proteins, fats, and nucleic acids are found to be essentially to same in all organisms, apart from minor variations.

– These processes demonstrate the fundamental unity of all living matter, and are collectively described as primary metabolism, with the compounds involved in pathways being termed primary metabolites.

Primary Metabolisms

Primary Metabolisms

Degradation of carbohydrates and sugars generally proceeds via the well characterized pathways, known as glycolysis and the kerbs / citricacid / tricarboxylic acid cycle, which release energy from the organic compounds by oxidative reactions.

Oxidation of fatty acids from fats by the sequence called β-oxidation also provides energy.

Primary Metabolisms

Aerobic organisms are able to optimize these processed by adding on a further process, oxidative phosphorylation. This improves the effeiciency of oxidation by incorporating a more general process applicable to oxidation of a wide variety of substrates rather then having to provide specific process for each individual substrate.

Primary Metabolisms

Proteins taken in via the diet provide amino acids, but the proportions of each will almost certainly vary from the organism’s requirements.

Most organisms can synthesize only a proportion of the amino acids they actually require for protein synthesis. Those structures not synthesized, so-called essential amino acids, must be obtained from external sources.

Secondary Metabolisms

The compounds which synthesized from the secondary metabolisms are so-called secondary metabolites.

Secondary metabolites are formed in only specific organisms, or groups of organisms, ane are expressioin of the individuality of species.

Secondary metabolites are not necessarily produced under all conditions, and in the vast majority of cases the function of these compounds and their benefit to the organism is not yet known.

It is this area of secondary metabolism that provides most of the pharmacologically active natural products.



To make such compounds as sugars, waxes, lignin starch, pigments, or alkaloids, plants utilize very specific enzymes, each of which catalyzes a specific metabolic reaction.The enzymes are proteins called organic catalysts.These enzymes are coded by specific genes in the plants DNA and

are made via processed we call transcription and traslation.When there is a series of enzymatically catalyzed reaction in a well-

defined sequence of step, we have what is termed a metabolic pathway.

Biosynthetic Pathway

Biosynthetic Pathway

Nucleoside diphosphate sugar pathway: cellulose, hemicellulose, glycosides.

Shikimate-cinnamate pathway: lignin, lignans, hydrolyzed tannins.

Mixed pathways of 3 and 4: some prenylflavonoids, quinones and stilbenes.



Primary and secondary metabolites leave a “grey area” at the boundary, so that some groups of natural products could be assigned to either divisions. Primary metabolites → Biochemistry Secondary metabolites → Natural products Chemistry

The classes of Secondary Metabolites

The classes of Secondary Metabolites

The majority of secondary metabolites belong to one of a number of families, each of which have particular structural characteristics arising from the way in which they are built up in nature (biosynthesis).

The classes of secondary metabolites are:Polyketides and fatty acidsTerpenoids and steroidsPhenylpropanoidsAlkaloidsOthers (specialize amino acids and carbohydrates)

Polyketide and Fatty Acids


Polyketides are formed by the linear combination of acetate units derived from the “building block” acetyl co- enzyme A.

The acetate origin of these compounds leads to a preponderance of even-numbered carbon chains.

Many plant oils and animal fats contain long-chain monocarboxylic acids know as fatty acids.

In the fatty acids, the carbonyl group of the acetate units is reduced during the course of the chain assembly process. Dehydrogenation and oxidative processed may subsequently give the unsaturated fatty acids.


The common fatty acids have an even number of carbon atoms, typically C12 – C20, linked together in a straight chain with up four double bonds.

In plants the fatty acids and the corresponding alcohol are found in leave waxes and seed coating:Myristic acid (C14) is found in nutmeg seeds.Palmitic acid (C16) is found in almost all plant oils.Stearic acid (C18) occurs in long amounts in animal fat.


Unsaturated fatty acids are important to us in food. Oleic acid is the most widely

distributed, and a major constituent of olive oil.

Linoleic and linolenic acids are most highly unsaturated and are found in linseed oil.

Linolenic acid is easily oxidized by air, and is one of the “drying oil” used in paint and varnishes


Linolenic acid is oxidized by plants to jasmonic acid, which is a signaling substances that stimulates plant defense mechanisms.

Arachidonic acid (C20) is a precursors of the prostaglandin hormones.


Polyacetylenes They are a group of naturally occurring

hydrocarbon derivatives characterized by one or more acetylenic groups in their structures.

Araliaceae, Campanulaceae, Apiaceae, Asteraceae, Pittosporaceae, and some

fungi.

Done byMohammed Amir Abdul Rahman YoussefMahmoud Amir Abdul Rahman Youssef

Science

Secondary Metabolites from Plants