434 phg 434 phg recent approaches in medicinal plants analyses
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Recent Approaches in Medicinal Plants Analyses
The use of plant-derived medicinals 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, marine, animals,- etc. (totally obtained from nature).
* e.g. of plant origin: Alkaloid and glycoside, volatile or fixed oil.
2- Semisynthetic substances: These are drugs that are manufactured by partial synthesis. A natural starting material can be modified by chemical or biochemical means to produce a substance having specific pharmacological activities. e.g. steroidal hormones and corticosteroids.
3- Synthetic substances: These are drugs which are manufactured by total synthesis (i.e. complete synthetic process or processes).
Medicinal plants information sources
1- Herbals: These are documents (books, manuscripts,.etc) that provide information about the uses of many plants in folk medicine. 2- Medical botany These are published books and periodicals ascribing the native flora of various regions of the world and the medicinal uses for each plant.
- It also may include the synonyms of plants and the constituents.
Many countries, nowadays are represented by books or review publications on medicinal botany. e.g. Flora of Saudi Arabia (Dr. Mijahid) 3- Ethnobotany
This means the study of the plants in their relationship to human.
Many report describing the habitual use and relationship of man and the surrounding flora are available.
4- Herbaria (herbarium)
Herbarium is a representative whole plant or organ of plant which is preserved to provide a reference specimen when required.
Information about: 1-The name (including synonymous names). 2-Date and place of collection. 3-Any field notes that the collector could gather the information including their: use and toxicity (if any) should be recorded on the so called Herbarium sheet. 5- Phytopharmacological surveys:
These are surveys which are concerned with the biological activities of plant extracts or constituents and they are available in specialized periodicals or books.
When we need to know the biological activities and or chemical constituents of plants? To achieve one or more of the following goals: 1- The discovery of new therapeutic agents.
2- The disclosing of new sources of economic materials for the synthesis of complex chemical substances. 3- Isolation of a novel chemical structure often prompts the chemist to a successful synthesis of a series of synthetic compounds which may have some medicinal value.
5- The knowledge of the chemical constituents of plants and their chemical structure will help studying their biosynthetic mechanisms and hence may facilitate their synthesis in laboratories. 6- Knowing the chemical constitutes of plants would help expanding the area of chemotaxonomy.
4-The knowledge of the chemical constituents of toxic plants will certainly help treating their poisonous effect to humans and animals.
To carry phytochemical study 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, 1H-NMR and 13C-NMR).
Selection of promising plant materials:
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 plantCultivated plantDisadvantageAdvantage1- Scattered in large or unlimited areaPresent in limited area.2- Difficult to reachEasy to reach3- The collector must be highly skilled botanistsThe collector must not be skillful person 4- Deficiency may occur due to continuous collection Continuous supply
Rules for collectionThe material is best collected when the organ in question has reached its optimal state of development:
1- Roots and rhizomes are collected at the end of the vegetation period, i.e. usually in the autumn.
2- Bark is collected in the spring.
3- Leaves and herbs are collected at the flowering stage.
4- Flowers are usually gathered when fully developed.
5- Fruits and seeds are collected when fully ripe.
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.
The most advantages time of collection is when the plant containing the active principals is highest in its content, example:
1- Time of year e.g. Hyoscyamous contain less amount of alkaloids in winter than in summer.
2- Time of the day e.g.1 Cardiac glycoside in Digitalis leaves are in higher amount at afternoon than in the morning. e.g.2 Solanaceous plants have higher quantities of alkaloids in the morning than in the afternoon.
3- Stage of maturity e.g. Solanaceous plants have higher quantities of alkaloids when collected in the flowering stage.
b- The collected plant should be free from any contamination. The main causes of contamination are: i- Collection of mixtures of plants by error. ii- Collection of closely similar species growing side by side and incorrectly assumed to be the same. iii- Collection of plants which it has a parasite within it.
c- Collecting plants which are free from diseases (i.e. which are not affected by viral, bacterial, fungal infection). This may cause:
i- Infection may seriously alter plant metabolism and unexpected products could be formed possibly in large amounts (causing confusion). ii- Infection may cause the presence of products of microbial synthesis (causing confusion).
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 materialsDrying The most common method for preserving plant material is drying.
Enzymatic processes take place in aqueous solution. Rapid removal of the water from the cell will, therefore, largely prevent degradation of the cell constituents.
- Drying also decreases the risk of external attack, e.g. by moulds.
Note: Drying should be carried out as quickly as possible without using high temperatures to prevent chemical changes of thermo-labile constituents e.g. volatile oils.
Living plant material has a high water content: * leaves may contain 60-90% water. * Roots and rhizomes 70-85%. * Wood 40-50%. * The lowest percentage is found in seeds, often no more than 5-10%.
Drying is done in:
-Shade and in sunlight (Natural drying). - Hot air drying or by freeze-drying (Artificial drying).
Aim of drying:
1- Ease of transport. 2- Ease of grinding 3- Inhibit the growth of microorganisms. 4- Preservative of active constituents.
Changes may occur during the drying:1- Size and weight: Drug when drying will be smaller in size and lose 80-90 % of their original weight.
2- Shape and appearance: Black pepper on drying show polygonal reticulation (due to presence of stone cell in the hypodermis)
3- Color: Tea leaves change from green to dark brown, almost black.
5- Active constituent: Slow drying of vanilla pods lead to obtain vanillin from glucovanillic alcohol. 4- Odor: Vanilla pods odorless when fresh and on drying acquire a fragrant, pleasant aromatic odor due to liberation of vanillin which has a charr. or nice odor.
5- Grinding of the dried plantsThe plant is grinding into small particle size to facilitate extraction.
Large particles take a longer time for complete extraction than small ones.
6- Garbling of the dried plants
Garbling is the final step in the preparation of a crude drug.
Garbling consists of the removal of extraneous matter, such as other pa