ISOLATION, PURIFICATION AND SCREENING OF

PLANT CONSTITUENTS

DR.U.SRINIVASA. M.Pharm, Ph.D

INTRODUCTION

The use of plant-derived medicinal dates

back many centuries although it is still

under estimation in modern medicine.

Plants remain the most important source

of natural drugs. More than 30% of

prescription drugs are natural products.

More than 60% of anticancer and anti-

infective drugs are natural products.

SOURCES OF DRUGS

1.Natural substances: From plants,

microorganisms, animals etc. (totally

obtained from nature).

2. Semi synthetic substances: These are

drugs that are manufactured by partial

synthesis.

3. Synthetic substances: These are drugs

which are manufactured by total synthesis

(i.e. complete synthetic process or

processes)

MEDICINAL PLANTS INFORMATION SOURCES:

Information, however can be obtained from one or more of the following sources:

1- Herbals

2- Medical botany

3 - Ethnobotany

4 - Herbaria (herbarium)

5 - Field exploration

6 - Phytopharmacological surveys

PHYTOCHEMICAL SCREENING – To carry phytochemical screening the following points

must be fulfilled:

1- Selection of promising plant materials.

2- Proper collection of selected plants.

3- Authentication of plant material.

4- Drying of plant materials.

5- Grinding of the dried plants.

6 - Garbling of the dried plants

7 - Packing, storage and preservation

8 - Extraction and fractionation of constituents.

9 - Methods of separation and purification.

10 - Methods of identification of isolated compounds

(Structure elucidation e.g. UV, IR, MS, H-NMR and C-NMR)

SELECTION OF PROMISING PLANT MATERIALS: Before investing time, effort and money

in phytochemical screening it is very important to select a promising plant.

The choice of promising plant depends upon the following:

1- A plant which have a biological activity.

2- A plant used in folk medicine.

3- A plant which show a particular

toxicities

IDENTITY Identity can be achieved by macro- and

microscopical examinations. Voucher

specimens are reliable reference sources.

Outbreaks of diseases among plants may

result in changes to the physical

appearance of the plant and lead to

incorrect identification. At times an

incorrect botanical quality with respect to

the labeling can be a problem.

Drug may be collected from: 1 - Wild plants. 2 -

Cultivated plants. Wild plant Cultivated plant

Disadvantage Advantage

Scattered in large or unlimited area

Present in limited area

Difficult to reach Easy to reach

The collector must be highly skilled botanists

The collector must not be skillful person

Deficiency may occur due to continuous collection

Continuous supply

PROPER COLLECTION OF SELECTED PLANTS

The following precautions should be considered during stage of collection:

1.The proper time of the day, time of the year and

maturity stage of collection is particularly

important because the nature and quantity of

constituents may vary greatly in some species

according to the season and time of collection

2.The collected plant should be free from any

contamination.

3.Collecting plants which are free from diseases

(i.e. which are not affected by viral, bacterial,

fungal infection).

Authentication of plant material : This may be confirmed by:

1. Establishing the identity by a taxonomy

experts.

2.Collection of a common species in their

expected habitat by a field botanist.

3. By comparing the collecting plant with a

voucher specimen ( herbarium sheet).

Drying of plant materials

Aim of drying:

1. Ease of transport.

2. Ease of grinding

3. Inhibit the growth of microorganisms.

4. Preservative of active constituents.

Drying is done in:

Shade and in sunlight (Natural drying).

Hot air drying or by freeze-drying (Artificial drying).

Extraction and fractionation of constituents :

There is no general (universal) method for the

extraction of plant materials.

The precise mode of extraction depends on:

1- The texture of the plant material.

2- The water content of the plant material.

3- The type of substances to be extracted or

nature

of active constituents.

EXTRACTION:

Is the separation of medicinally active portion of

plants or animal tissues through the use of

selective solvent and suitable methods extraction.

The principal methods of extraction are:

1 - Macération

2 - Percolation

3 - Infusion

4 - Decoction

5 - Digestion

5 - Digestion

6 - Continuous hot extraction ( Soxhlet

extraction procèss).

7 - Liquid-liquid extraction

8 - Solvent-solvent ppt.

9 - Distillation

MACERATION :

1.In maceration powdered drug is soaked

in organic solvent and kept for about 24

hrs , sometimes 3-4 days also, depending

upon the part of the plant to be

extracted.

2.The solvent is decanted, filtered and

concentrated.

PERCOLATION :

In percolation special types of percolators

are used. These are funnel shaped. The

solvent continuously percolates through ,

the coarse particles of the drug. Solvent is

collected, filtered and concentrated.

DECOCTION :

In case of decoction , the powdered plant

material is boiled with the solvents .It is

collected and filtered. Filtered solvent is

concentrated.

Eg. Preparation of tea.

Continuous hot extraction technique (Soxhlet extraction procèss )

Successive solvent extraction :

Petroleum ether (60-80)

Benzene

Chloroform

Acetone

Ethanol (95%)

Chloroform water