Textbook of pharmacognosy and phytochemistry 1st Edition unsecured

432 TEXTBOOK OF PHARMACOGNOSY AND PHYTOCHEMISTRY
Isolation of Strychnine
100 g of powdered nux vomica seeds are mixed thoroughly
with 100 ml of 10% calcium hydroxide in water and left
overnight at room temperature. The air dried slurry is
extracted with chloroform in a soxhlet extractor for 3 h.
The chloroform solution is then extracted several times
with 5% sulphuric acid solution and subsequently basified
with 10% aqueous sodium hydroxide solution. Cooled and
the crystals are filtered. Required amount of 50% ethanol is
added, and the mixture is refluxed until most of the solid
has dissolved. The solution is filtered after adding charcoal.
The filtered crystals of strychnine are washed with a little
50% ethanol. The mother liquor and washings are used
for the isolation of brucine.
The crude strychnine is dissolved in 9 volumes of boiling
water, and 15% sulphuric acid solution is added slowly with
stirring, until the reaction is slightly acid to Congo red.
Activated charcoal is added to the solution and the solution
is refluxed for 1 h and filtered hot. On cooling strychnine
sulfate crystallizes out, filtered and washed with cold water.
The obtained crystals are dissolved in 15 volumes of water,
heated at 80°C and neutralized with 10% aqueous sodium
carbonate: after addition of charcoal, the solution is filtered
hot. Strychnine precipitates on addition of aqueous sodium
carbonate and cooling. The precipitate is filtered and washed
with cold water. It is re-crystallized using ethanol.
Melting point: 286–288°C
Isolation of Brucine
The mother liquor remaining after separation of strychnine
is concentrated in vacuo on a water bath until most of the
alcohol is removed. The residue is acidified to pH 6 with
dilute sulphuric acid and then concentrated to a volume of
3–4 ml overnight. It is kept in a refrigerator and the product
is filtered and washed with cold water. Adding 4.5 volumes
of hot distilled water and boiling with a little charcoal for
1 h purify brucine sulfate. It is filtered while hot and kept
in a refrigerator for several days. Brucine is recovered from
the sulfate using the similar procedure used for strychnine.
It is re-crystallized using aqueous acetone.
Melting point: 178°C
Identification Tests
1. Strychnine when treated with sulphovanadic acid gives
purple red colour.
2. Strychnine when treated with sulphuric acid and
crystals of potassium dichromate gives purple colour,
which slowly changes to red, while brucine gives
immediate red colour.
3. Brucine when treated with nitric acid gives blood red
colour, which is discharged by the addition of stannous
chloride solution.
Thin Layer Chromatography of Strychnine
and Brucine
Both the alkaloids are dissolved in methanol and spotted
in silica gel-G plate. The solvent system used is benzene:
Chloroform: diethylamine (9:4:1). After the development
the plate is sprayed with Dragendroff ’s reagent, R f
values
of both the alkaloids corresponds respectively.
25.30. ISOLATION OF VASICINE
Vasicine is a pyrrolazoquinazoline alkaloid obtained from
the leaves of Adhatoda vasica; family Acanthaceae. A. vasica
known as vasaka is a highly reputed ayurvedic medicinal
plant used for the treatment of respiratory ailments, particularly
for the treatment of cough, bronchitis, asthma and
tuberculosis. Vasicine is present in vasaka upto about 1.3%.
The other alkaloids present include vasicinone, vasicinol,
vasicinolone, vasicol and adhatonine.
Isolation
N
Vasicine
Vasaka leaves are dried, coarsely powdered and basified to
pH 9 with ammonia solution. It is further extracted with
chloroform. The total chloroform extract is combined and
washed with water and dried over anhydrous sodium sulphate.
The solvent evaporated to get the total alkaloid extract
containing vasicine as a major alkaloid. Vasicine can be
further purified from the dry extract by crystallization.
Melting point: 210°C
Thin Layer Chromatography of Vasicine
Dissolve 1 mg of vasicine in 1 ml of methanol with little
warming. Apply the spots of test solution on the silica gel-G
plate and elute with toluene–methanol–dioxane–ammonia
(1:1:2.5:0.5). Spray the dried TLC plate with Dragendorff ’s
reagent. Vasicine gives orange coloured spot.
N
OH
25.31. ISOLATION OF VINCA
ALKALOIDS
Vinblastine is isolated from the dried entire plant of Catharanthus
roseus Linn (Apocynaceae).
Extraction and Isolation
The dried leaf material is taken and is extracted with a
solution of hot ethanol–water–acetic acid in a ratio of 9:1:1.
The solvent is removed and to the residue hot hydrochloric
acid solution of 2% is added. The pH of the acidic extract
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