Date post: | 13-May-2015 |
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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