Alkaloids-Classification,testing And Isolation

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Chemical nature

They are nitrogenous bases with tertiary amines having an alkaline pH. They occur as salts of nicotinic, quinic, citric, or oxalic acid.

General characters

  • They are white crystalline substances

  • Insoluble in water except for certain salts

  • They have a sharp melting point

  • They are mostly poisonous, but exert useful physiological effects when used in small quantities.

  • They are bitter to taste

Isolation of alkaloids

Alkaloids can be extracted by simple acid-base extraction.

Procedure

  • Step 1

Drug to be tested is powdered and moistured with lime water, so that acids, tannins, phenols are removed

  • Step 2

       The mixture is extracted with organic solvents like alcohol

  • Step 3

The organic lipid now contains alkaloidal salts, which can be isolated easily.

Classification of alkaloids

They are broadly classified into

  • Proto or pseudo alkaloids

  • True or heterocyclic alkaloids

Pseudo alkaloids

The examples for pseudo alkaloids are ephedrine, colchicines, aconitine etc

True alkaloids

They are again subdivided into

  • Indole alkaloids eg. Strychnine, reserpine, ergotamine.

  • Steroidal alkaloids e.g. Conicine, withanine.

  • Quinoline alkaloids eg.quinine, quinidine.

  • Pyridine alkaloids e.g. Trigonelline.

  • Pyrrolidine alkaloids e.g. nicotine

  • Tropane group e.g. Atropine, cocaine

  • Iso-quinoline group e.g. Papaverine, narcine, berberine.

  • Phenanthrene group e.g. Morphine, codeine.

  • Phenethylamine group eg.ephedrine

  • Purine group etc eg caffeine

  • Other than these there are quaternary ammonium compounds like choline, neurine, muscharine.

Naming of alkaloids

The alkaloids may be named after,

  • Genus name e.g. Withanine

  • Species name e.g. Somniferine

  • Commercial name eg.ergotamine

  • Discoverer name eg.pelletierine

  • Action e.g. morphine etc

Distribution

  • Apocyanaceae

  • Amarydillaceae

  • Rutaceae

  • Rubiaceae

  • Ranunculaceae

  • Fabaceae

  • Solanaceae

  • Liliaceae

  • Papaveraceae

Etc.

Test for alkaloids

  • Meyer`s test

            Whitish yellow or green precipitate

  • Wagener’s test

             Dirty brown or red precipitate

Uses

These alkaloids are associated with prevention or treatment of major diseases like cancer, diabetes, hypertension, AIDS, etc.

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