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Reserpine is an indole alkaloid the active principle of Rauwolfia species
Reserpine is obtained from roots of Rauwolfia serpentina, Rauwolfia micrantha, R. vomiforia and R. tetraphylla
Chemical investigation of around 60 different Rauwolfia species led to the isolation of 50 -70 Rauwolfia alkaloids; of which the most important ones are
Reserpine,
Rescinnamine
Yohimbine,
Ajmalicine, and ajmaline.
The snake-like roots of Rauwolfia is used for
Controlling hypertension,
Epilepsy,
Insomnia,
Fevers,
Cholera,
Dizziness, and headaches.
Properties of reserpine are:
It has a melting point of 265ºC.
It is stable, but gradually darkens on exposure to light.
It is combustible.
It is incompatible with strong acids, reducing agents, and oxidising agents.
It exists as white or cream to slightly yellow crystals or crystalline powder.
It has no odour and has a bitter taste
Isolation Reserpine can be isolated by following the below-mentioned steps:
Rauwolfia root powder is extracted with 90% alcohol by percolation.
The alcoholic extract is concentrated and dried under reduced pressure below 60°C temperature to yield rauwolfia dry extract that contains 4% of total alkaloids.
This dry extract is again extracted with proportions of ether:chloroform:alcohol (20:8:2.5).
The extract obtained is added with little dilute ammonia with alternating shaking to convert the alkaloid into water-insoluble base.
Water is added to the above mixture and the drug is allowed to settle after a few vigorous shakings.
The solution is filtered and the residue is extracted with 4 volumes of 0.5M H2SO4 in a separating funnel.
The total acid extract containing the alkaloidal salt is combined.
The extract is filtered, made alkaline with dilute ammonia to liberate the alkaloid.
The resulting alkaline solution is extracted with chloroform.
The total chloroform extract is filtered and chloroform is removed by distillation.
The total alkaloidal extract is dried under vacuum to yield total rauwolfia alkaloids (consists of a mixture of over 30 different components).
Melting point: 270°C.
Thin-layer chromatography of Reserpine:
1 mg alkaloidal extract or purified Reserpine is dissolved in methanol.
The silica gel-G TLC plates are spotted and eluted in solvent system chloroform-acetone-diethylamine (5:4:3).
In the case of alumina-G plates, elute the plates in solvent system cyclohexane-chloroform (3:7).
Then eluted plates are dried and sprayed with Dragondorff’s reagent.
The alkaloidal component gives an orange spot in both cases.
The Rf value of Reserpine is 0.72 (in silica gel-G stationary phase) and 0.35 (in alumina-G stationary phase).
Identification Test:
A red colouration along the medullary rays is observed when the freshly fractured surface is treated with concentrated nitric acid.
Reserpine shows a violet red colour when treated with a solution of vanillin in acetic acid.
On treatment with a solution of vanillin in acetic acid, reserpine shows violet red colour.
Reserpine is colourimetrically determined by reaction between acidic solution of alkaloids and sodium nitrite.
Analysis HPLC Analysis: Water (0.1% CH2O2 and 0.1% triethylamine; pH 5.0, adjusted with NH4OH and H 3PO4) as solvent A and acetonitrile (0.1% CH 2O2 and 0.1% triethylamine) as solvent B are used as the mobile phase. Both the solvents are filtered through a millipore PTFE 0.45μm membrane. Separations are carried out using a linear gradient: 0 min 50% B, 3 min 50% B, 3.10 min 55% B, 6 min 55% B, 6.10 min 100% B, 7 min 100% B, 7.10min 50% B, and 10 min 50% B. Flow rate of mobile phase is 1.0ml/min, and the injection volume is 20μl. Chromatographic runs are carried out at 25ºC. UV detection is performed at 268nm.
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