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Renin Angiotensin Mechanism.

Chemical Nature Of Crude Drugs: Alkaloids

Chemical Nature Of Crude Drugs.

Alkaloids

  • Definition: Alkaloids are basic nitrogenous organic compounds of the plant origin, having marked physiological action when taken in the small dose and containing one or more than one nitrogen in a heterocyclic ring.
  • Physical Properties:
  • They are colorless crystalline, non – volatile & bitter in taste.
  • They are solid, insoluble in water, soluble in organic solvents.
  • Generally, they are levorotatory.
  • There are some exceptions Coniine is dextrorotatory. Nicotine is liquid and Berberine is yellow.
  • Alkaloids found as salts of organic acids in the plant.
  • Biological Role: -
  • 1) They protect the plant from insects and animals
  • 2) They take part in protein synthesis.
  • 3) They stimulate and regulate growth, reproduction & metabolism of the plants.
  • 4) They are detoxicating agents.
  • 5) They act as a nitrogen reservoir for the plant.
  • Identification Tests: -
  • There are two types of tests.
  • 1) Precipitation tests.
  • 2) Colour tests.     
  1. Precipitation tests:-
Mayer’s Test
Alkaloid + Mayer’s reagent
(Mayer’s reagent: Potassium mercuric iodide solution)
Cream Color or ppt
Dragendorff’s Test
Alkaloid + Dragendorff’s reagent
(Dragendorff’s reagent: Potassium Bismuth iodide solution)
Brown or reddish Brown ppt. Or colour
Wagner’s Test
Alkaloid + Wagner’s reagent
(Wagner’s reagent: Iodine & pot. Iodide solution)
Brown or reddish brown ppt or color.
Hager’s Test
Alkaloid + Hager’s reagent
(Hager’s reagent: Saturated solution. of picric acid)
yellow ppt.

  • Colour Tests: -
  • a) Potassium chlorate + Caffeine + a drop of HCl – It gives a purple color.
  • b)Colchicine + HNO3 – yellow color.

CLASSIFICATION OF ALKALOIDS:-
  • Alkaloids can be classified by two methods:
  • 1) Classification based on pharmacological actions.
  • 2) Classification based on a chemical nucleus.
  • 1) Classification based on pharmacological actions:
  1. Antimuscarinic: Atropin, Hyoscine.
  2. Anthelmintic: Emetine.
  3. Anticancer: Vincristine, Vinblastine.
  4. Adrenergic: Ephedrine.
  5. CNS Stimulants: Caffeine, Strychnine.
  6. Analgesics: Morphine, Codeine.
  • 2) Classification Based on a chemical nucleus:


Types of alkaloids
Example
Sources
1. Tropane.
Atropine, cocaine
Datura, Coca
2. Quinoline.
Quinine, Quinidine
Cinchona
3. Isoquinoline.
Papaverine, Emetine
Opium, Ipecac
4. Indole.
Strychnine, Brucine, Reserpine
Nux-vomica, Rauwolfia, Vinca
5. Phenanthrene.
Morphine, Codeine
Opium
6. Purine.
Caffeine
Tea, Coffee.
7. Pyrrole and pyrrolidine.
Nicotine
Tobacco
8. Pyridine and Piperidine.
Coniine, Lobeline
Hemlock, Lobelia.
9. Imidazole.
Pilocarpine
Pilocarpus.
10. Steroidal.
Conessine, Solanin
Kurchi, Potato.
11. Terpenoids.
Aconitine
Aconite
12. Alkaloidal Amines. (Protoalkaloids)
Ephedrine, Cholchicine
Ephedra, Colchicum

Extraction of Alkaloids

  • Method of Isolation depends upon chemical nature of Alkaloid
  • Method I
  • 1) The drug is powdered & extracted with ethyl alcohol.
  • 2) Remove the solvent by evaporation.
  • 3) Treat the residue with water.
  • 4 )Separate the water containing free bases.
  • 5) Add sodium carbonate & extract the solution with Ether.
  • 6) Evaporate the Ether to obtain crude product.
  • 7) Pure these alkaloids by chromatography.
  • Method II:
  • 1) Powder of drug is treated with water & lime.
  • 2) The lime combines with acid, Phenolic substances, & tannins.
  • 3) The powder is extracted with ether.
  • 4) The ether is shaken with water & alkali.
  • 5) The impurities go in ether solution.
  • 6) The crude alkaloids come in aqueous soln.
  • 7) This solution is again extracted with chloroform to obtain pure alkaloids.
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