Ghada Ali AL-Hussiany
Pharmacognosy
Lecture ( 8 )
Chemistry of natural drugs products
The living organism may be a biosynthetic laboratory not only for chemical compounds (carbohydrates, Protein, fats) which are used as food by humans &animals, also for compound (glycoside,alkaloids,terpenoids)which have a physiological effect,thatgive plants&animals drugs their therapeutic properties &these drugs are used as such in their crude form ,or may be extracted &used as medicinal agent, these chemical compound termed constituents .These constituents are either are either active or inert which occur in plant &animal drugs .Cellulose , lignin , suberin &cutin are usually inert matter in plant drugs . Starch ,albumin , coloring matters & others substances may have no definite pharmacologic activity &also are considered inert constituent. In animal drugs keratin ,chitin , muscle fiber &connective tissue are considered as inert .The presence of inert substances may be prevent or modify the absorbability or potency of the active constituents .To eliminate the undesirable effects of inert matter in the crude drug or its preparations , by extracted , crystallized & purified for therapeutic use ,these constituents referred to secondary plant substances .Active constituent are responsible for the therapeutic activity of the drug ,they may be single substance or mixtures e.g for the single chemicals glycosides ,terpenoids steroids ,phenylpropanoides alkaloids &peptides. The mixtures chemical include gums ,fixed oils, fats, waxes ,volatile oils ,resins &resin combination.
The secondary constituents of drugs plants are influenced by three principle factors:
1. Heredity (genetic composition )
2. Ontogeny (stage of development)
3. Environment
Genetic effects induce both quantitative &qualitative change but those caused by enviromntal influences are primarly quantitative.
Plants of the same species thatresemble one to another closely in form &structure (phenotypically ),never different in gentic composition (genotypically ,the result in distinct differences in chemical composition particularly with secondary constituents.e.g ergot fungus Claviceps purpurea isolated a single desired alkaloids ergotamine ,other example include Eucalyptus content volatile oil cineole &related constituents .Straphanthus sarmeatosus content glycosides &sapogenins.
Ontogeny plays a significant role in the nature of the active constituents found in medicinal plants .The concentration of secondary metabolites would be increase with the age of the plant e.g The cannabidiol content of cannabis sativa reaches a peak early in the growing season &then begins to decline ,when this decline occurs ,the concentration of tetrahydro cannabinol begins to increase reciprocally &continues until the plant approaches maturity ,old plants are characterized by high concentration of cannabinol .
Opium poppy ,papaver somniferum ,the morphine content of the capsules is highest 2-3 weeks after flowering .If the latex is harvested earlier ,related alkaloids such as thebaine &codeine predominate while if harvesting is delaying to long ,the morphine decomposes .
Environmental factors that can produce variations in secondary plant constituent ,include soil ,climate ,associated flora &methods of cultivation ,so because of these fctors are more or less related ,they are difficult to evaluate individually e.g many plants containing alkaloid higher concentration in moist regions than in arid lands , this may be related to the soil ,which is usually poor in nitrogen in arid regions &rich nitrogen sources are usually required for good yield of alkaloids.But this not apply for the plant contain volatile oil because excess nitrogien dose not necessarily cause an increase in their yields ,so plants abound in dry areas as opposed to moister habitate.
Drug biosynthesis or biogenesis is the study of the biochemical pathways leading to the formation of secondary constituents used as drugs.
The biosynthesis pathways leading to the formation of secondary constituents used as drugs &then subject to scientific investigation.