Textbook of pharmacognosy and phytochemistry 1st Edition unsecured

Isolation of
Phytopharmaceuticals
CHAPTER
25
25.1. INTRODUCTION
There is a revival of interest in the use of plants in pharmacy
both from pharmaceutical industry as a source of new lead
molecules find from the general public who are using plant
extracts in many ways in conventional and complementary
therapies. About one-quarter of all prescription drugs are of
plant origin despite the fact that less than 5% of plant species
have been investigated. Many of the synthetic medicine
currently in clinical use have been from natural sources.
It is a widely accepted fact that natural product chemistry
surpasses the kind of chemistry that synthetic chemist can
ever accomplish in the laboratory. Phytochemical diversity
in terms of structural novelty is unprecedented in laboratory
synthesis. Indeed the plant kingdom provides enormous
chemical diversity. Advances in bioassay screening, isolation
techniques and structural elucidation have greatly shortened
and accelerated the process of drug discovery from
medicinal plants. Nowadays it is a common practice among
natural product chemists to use some type of bioassay to
direct the progress of phytochemical investigation towards
the discovery of new pure bioactive markers.
The increasing use of herbal preparations has highlighted
need for adequate standards to ensure quality, safety and
efficacy of such drugs and preparations. Many developing
countries are becoming aware of the potential of their flora
as a source of medicinally useful products. Some of the most
important alkaloids, glycosides, aglycones, resin and essential
oil components of commercial use have been presented
here in respect to their isolation and identification.
25.2. ISOLATION OF ATROPINE
Atropine is a tropane alkaloid from the members of the
Solanaceae family. It is present in Atropa belladona (Deadly
Night shade), Datura stramonium (Thorn apple), and Hyoscyamus
niger (Henbane), Other important solanaceous alkaloids
are hyoscyamine, hyoscine (scopolamine), apoatropine,
belladonine and norhyoscyamine. Atropine is an optically
inactive laevorotatory isomer of hyoscyamine.
Isolation
CH 3
N
O
Atropine
O
C
CH2OH
Atropine is isolated from the juice or the powdered drug.
Hyoscyamus muticus is the preferred source for the manufacture
of atropine because of its high alkaloidal content,
with D. stramonium next in order.
The powdered drug material is thoroughly moistened
with an aqueous solution of sodium carbonate and then
extracted with ether or benzene. The alkaloidal free bases are
extracted from the solvent with water acidified with acetic
acid. The acid solution is then shaken with solvent ether
to remove colouring matter. The alkaloids are precipitated
with sodium carbonate, filtered off, washed and dried. The
dried mass is dissolved in solvent ether or acetone and dehydrated
with anhydrous sodium sulphate before filtration.
The filtrate after concentration and cooling yields crude
crystals of hyoscyamine and atropine from the solution.
The crude crystalline mass is separated from the solution.
The crude crystalline mass obtained after filtration is dissolved
in alcohol, and sodium hydroxide solution is added
and the mixture is allowed to stand until hyoscyamine is
completely racemized to atropine which is indicated by the
absence of optical activity.
C
H
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