Classification of drugs (Chemotaxonomy)

• Definition and goals of chemotaxonomy

• Factors involved in chemotaxonomy

• Applications of chemotaxonomy

• Methods in chemotaxonomy


At the end of this tutorial, student will be able to

• Define chemotaxonomy

• Discuss the factors involved in chemotaxonomy

• Discuss the applications of chemotaxonomy

• Explain and discuss the various methods in chemotaxonomy


Chemical Plant Taxonomy / Chemosystematics

• Approach of taxonomy in which the chemical features of plants are used in developing classification or in solving the taxonomical problems is called chemotaxonomy

• Attempt to classify and identify organisms (originally plants), according to demonstrable differences and similarities in their biochemical compositions

• Establishes a relationship between position of plant (taxonomy) and attempts to utilize the chemical facts for more exact understanding of the biological evolution and relationship

Reason for rapid growth and purpose of Chemotaxonomy

• Chemical characters + traditional taxonomical system of classification

• Evidence from as many source as possible should be used

• Development of many new technologies

• Isolation and characterization of new compounds

• Biosynthetic pathways

Goal in Chemotaxonomy

• Chemical structures of the genes themselves

• Techniques - DNA hybridization, Serotaxonomy, Amino acid sequencing etc

Factors to be considered in Chemotaxonomy

• Parallelism

• Diversification

• Homology

• Parts of the plants

• Chemical characters


• Different groups of plants undergone a similar type of change


• Groups of related plants may have developed different characters

• Applicable to both chemical & morphological characters


• Benzoic acid in related plants

• Alkaloid sparteine in unrelated plants, Cytisus scoparius (Leguminosae) and Chelidonium majus (Papaveraceae)


• Related plants produce chemically Unrelated compounds with the Same biogenetic origin

Example: Alkaloid like substance Bakankosine of Strychnous vacacuo (Loganiaceae) homologus with nitrogen free iridoid like Swertiamarin (Loganiaceae) and Gentiopicrin (Gentianaceae)

Parts of the plants

• Not only age and degree of development, also the part of the plant used for analysis


• Composition of clove oil from flower bud differs from that of oil from blown clove

• Composition of cinnamon leaf oil differs from the oil obtained from cinnamon root or bark

Chemical Characters

• Universal occurrence - carbohydrates, amino acid - less considered

• Compounds known to occur in one species only are less considered Example: Coniine from Conium maculatum, is not found in any other plants, hence less considered

• Intermediate distribution - secondary modifications and rearrangement

Factors to be considered in Chemotaxonomy

Applications of chemotaxonomy

• Primary metabolites (widely distributed)

- Accumulation and form of accumulation

Example: Sucrose in Beta vulgaris, Sachharum officinalis

• Secondary metabolites (limited distribution)

• Macromolecules (proteins, enzymes)

• Secondary metabolites

Alkanes: Pristane Phytol

Fatty acids: Palm oil from the fruit wall has more of palmitic, oleic, linoleic esters whereas the seed oil has more of lauric and myristic acid


Glycosides: Commonest glycosides (O-glycosides) - C-glycosides

Phenolic compounds: Trihydroxy derivative of benzoic and cinnamic acid


Rhodoxanthin in yew berries

Capsanthin in capsicum

Nucleic acids

DNA of wheat, barley, rye when compared with that of the DNA of oat showed marked difference

Methods in Chemotaxonomy

• Serotaxonomy

• DNA hybridization

• Amino acid sequencing


• Approach or utility of serology

• Serology: antigen and antibody reaction

Antigen: Substance when introduced into the body stimulates the production of an antibody

Antibody: Protein found principally in blood serum and characterized by a specific reactivity with the corresponding antigen


• Preparation of antigen

• Production of antibody

• Extraction of antisera

• When the specific antisera and antigen are reacted, precipitation reaction occurs. The degree of precipitation relates to protein homology

Gel Diffusion Method

Plant A:  Antigen - X Y

Antisera - X1 Y1

Plant B: Antigen - Y Z

Antisera - Y1 Z1

Gel Diffusion Method

DNA Hybridization

DNA Hybridization

Amino acid Sequencing – Sangers Method

Amino acid Sequencing – Sangers Method

Amino acid Sequencing – Edmans Method

Amino acid Sequencing – Edmans Method

Other methods used are

• Restriction Fragment Length Polymorphism (RFLP) - to distinguish between species and hybrid of species.

Example: Duboisia sps, Panax sps

• Random Amplified Polymorphic DNA Analysis - to distinguish between various sub species

Example: Melissa officinalis


• The factors to be considered in chemotaxonomy includes parallelism, diversification, homology, chemical characters and age of the plant

• The chemical characters should not be of universal occurrence, should not be in only one plant and should be of intermediate distribution

• The methods used in chemotaxonomy includes Serotaxonomy, DNA hybridization, Amino acid sequencing, Restriction Fragment Length Polymorphism, Random Amplified Polymorphic DNA Analysis etc

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