B. Reserpine
Synonyms Crystoserpine; Eskaserp; Rau-sed; Reserpoid; Rivasin; Serfin; Sandril; Sedaraupin; Serpasil; Serpine; Serpasol; Serpiloid.
Biological Sources It is obtained from the plant Catharanthus roseus (L.) G. Don (Apocynaceae) (Periwinkle, Madagascar or Cape Periwinkle, Old Maid); root of Rauvolfia serpentina (L.) Benth (Apocynaceae) (Rauvolfia, Chandra, Sarpaganda); root of Rauvolfia tetraphylla L. (Apocynaceae) (Pinque-Pinque); and from the plant of Vinca minor L. (Apocynaceae) (Periwinkle).
Chemical Structure
(3β, 16β, 17α, 18β, 20α)-11, 17-Dimethoxy-18-[(3, 4, 5-trimethoxy benzoyl)oxy] yohimban-16-carboxylic acid methyl ester; (C33H40N2O9);
Isolation Reserpine may be isolated by adopting the following steps in a sequential manner:
1. The powdered and sieved roots are allowed to swell in a NaHCO3 solution (10% w/v) for a period of 10-12 hours. The resulting solution is extracted with benzene, until the extracts give a weak positive reaction with HgI2.
2. The combined benzene extracts are concentrated and ether is added to the benzene solution. The resulting mixture is extracted with dilute HCl. The combined acidic solution is washed with ether, filtered and extracted with chloroform in a successive manner.
Note: The chloroform will specifically extract the weakly basic alkaloids, such as: Reserpine and Rescinnamine.
3. The combined chloroformic extract is washed subsequently with 10% (w/v) sodium carbonate solution and followed by water so as to get rid of any free acids present. The resulting extract is finally evaporated to dryness under vacuo.
4. The residue is dissolved in anhydrous methanol and seeded with a pure crystal of reserpine and allowed to cool gradually when reserpine will crystallize out.
5. However, rescinnamine, deserpidine and other minor weakly basic alkaloids could be obtained from the mother liquor conveniently.
6. The mother liquor is evaporated to dryness, and the residue is dissolved in the minimum quantity of benzene and subjected to column chromatography over a column packed with acid-washed alumina. The alkaloids are eluted in the different fractions by making use of benzene, chloroform, methanol (10%) in a sequential manner.
Characteristic Features
1. It is obtained as long prisms from dilute acetone which get decomposed at 264-265°C; (decomposes at 277-277.5°C in an evac-tube).
2. Its specific optical rotations are: [α]23D - 118° (CHCl3); [α]26D - 164° (C = 0.96 in pyridine; [α]26D - 168° (C = 0.624 in DMF).
3. It has uvmax (CHCl3): 216, 267, 295 nm (61700, 17000, 10200).
4. Reserpine is weakly basic in nature, pKa 6.6.
5. It is found to be freely soluble in chloroform (~ 1g/6 ml), glacial acetic acid, methylene chloride; soluble in benzene, ethyl acetate; slightly soluble in acetone, methanol, ethanol (1g/1800 ml), ether, in aqueous solutions of citric and acetic acids; and very sparingly soluble in water.
Identification Tests
1. Most solutions of reserpine upon standing acquire a distanct yellow colouration and a marked and pronounced fluorescence; especially after the addition of an acid or upon exposure to light.
2. Reserpine Hydrochloride Hydrate (C33H40N2O9.HCl.H2O): It is obtained as crystals which decompose at 224°C.
Uses
1. It is a hypotensive drug which exhibits strong hypotensive and sedative activity.
2. It is also employed to alleviate mild anxiety conditions i.e., the drug shows a mild tranquillizing effect.
