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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.
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