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474 PHG
Screening, separation
and
analysis for plant
constituents
Dr. Areej M. Al-Taweel
Required Text book:
- Wagner, H., Bladt, S. & Zgainski, E. M, Plant Drug Analysis.
- Richard J. P. Cannnell, Natural Product Isolation.
- Robert M. Silverstein and Francis X. Webster, Spectrometric
Identification of Organic Compounds.
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.
The main sources of drugs are as follows:
1- Natural substances:
From plants, microorganisms, animals,- etc.
(totally obtained from nature).
2- Semisynthetic 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).
1. 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.
2. Proper collection of selected plants
Drug may be collected from:
1- Wild plants.
2- Cultivated plants.
Wild plant
Cultivated plant
Disadvantage
Advantage
1- Scattered in large or
unlimited area
Present in limited area.
2- Difficult to reach
Easy to reach
3- The collector must be highly
skilled botanists
The collector must not be
skillful person
4- Deficiency may occur due to
continuous collection
Continuous supply
The following precautions should be considered during
stage of collection:
a- 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.
b- The collected plant should be free from any contamination.
c- Collecting plants which are free from diseases (i.e. which
are not affected by viral, bacterial, fungal infection).
3- 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)
4- 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).
Changes may occur during the drying:
1- Size and weight
2- Shape and appearance
3- Color
4- Odor
5- Taste
6- Active constituent:
Slow drying of vanilla pods lead to obtain vanillin from
glucovanillic alcohol.
CH3O
CH2OH
CH3O
Enz
H2O
Glu-O
Glucovanillic alcohol (glucoside)
CHO
CH2OH CH3O
Enz
[O]
HO
HO
Vanillin
5- Grinding of the dried plants
6- Garbling of the dried plants
7- Packing, storage and preservation
8- 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- Maceration
2- Percolation
3- Infusion
4- Decoction
5- Digestion
6- Continuous hot extraction technique
(Soxhlet extraction process).
7- Liquid-liquid extraction
8- Solvent-solvent ppt.
9- Distillation
Continuous hot extraction technique
(Soxhlet extraction process)
Choice of solvent
As a general empirical rule:
 Non polar solvents (petroleum ether and hexane) will dissolve
non-polar compounds (fats and waxes).
While polar solvents (methanol, ethanol and water)
dissolve polar compound (alkaloid salts and sugars).
(that mean like dissolve like)
 The affinity of the solute for the organic phase may be
greatly increased by using mixture of solvents instead
of single ones (sometimes used mixtures of solvent to
increase the solubility).
Example: solublization of an aliphatic carboxylic acid in
ethanol, acetone and a mixture of both.
O------------H-O-CH
2-CH3
In ethanol -R-C
Hydrogen bond
O-H
O
In acetone R-C
Hydrogen bond
CH3
O-H---------O=C
CH3
In a mixture of acetone and ethanol
O
HO-C 2H5 (ethanol)
CH3
R-C
OH
O=C
(acetone)
CH3
Screening of Drugs
After a new substance (expected to be a new drug)
has been developed.
-The next step is to subject it to a specified set of
procedures in experimental animals.
 The aim is to determine whether or not the compound
possesses the desired action.
Phytopharmacological screening:
● Antimicrobial activity
Cinnamomum verum
Thymus vulgaris
Lavendula officinalis
(Eugenol)
(Thymol)
(Linalool)
● Antineoplastic activity
Catharanthus roseus
Taxus brevifolia
(Vincrestine, vinblastin)
(Taxol)
● Antimalarial:
Cinchona succirubra
Artemisia annua
(Quinine)
(Artemisinin)
Phytopharmacological screening:
● Hypoglycemic:
Garlic (Allium sativum)
(Allicin)
● Cardiotonic
Digitalis purpurea
Strophanthus kombe
(Digoxin and Digitoxin)
(K-strophanthoside)
● Antiarrythemic
Cinchona succirubra
(Quinidine)
Type of pharmacological screening:
1-Blind screening
2- Simple screening
3- Programmed screening
The organization of blind screening
Screening for pharmacological activities proceeds from
general observation on intact animals to the more specific
techniques using isolated organs.
It might include the following tests:
A- Preliminary observations on the behaviour of conscious
animals (neuropharmacological tests)
B- The cardiovascular test.
D- Isolated organ preparations especially the isolated
guinea pig ileum.