Isolation of Glycyrrhetinic Acid

Isolation of Glycyrrhetinic Acid: Glycyrrhetinic acid is a pentacyclic triterpenoidal glycoside (mainly aglycone) that is obtained from roots and stolons of Glycyrrhiza glabra belongs to the family Leguminosae. It is used as an antiulcer compound.

Coarsely powdered drug of Glycyrrhiza is extracted with chloroform. The chloroform extract is filtered and the filtrate is discarded. Then obtained marc is extracted with 0.5M sulphuric acid for a few hours. Filter it and the filtrate is extracted with chloroform (3 parts). Separate the chloroform layer and mix them. Then distill off the chloroform extract which will yield the dry residue of glycyrrhetinic acid.

In another method of extraction powdered liquorice is extracted with boiling water. The obtained aqueous extract is concentrated and dried. Then this extract is dissolved in water and acidified with hydrochloric acid (pH 3 to 3.4) to precipitate glycyrrhetinic acid. Then precipitate is filtered and washed with water up to neutral pH and dried. This will yield glycyrrhetinic acid.

Melting point: 300°C.

Thin-layer chromatography of Glycyrhetinic acid

1 mg of glycyrrhetinic acid is dissolved in 1 ml methanol chloroform (1:1) solvent. Then apply the spots on silica gel G plates and elute the plate in solvent system Toluene-ethyl acetate-glacial acetic acid (12:8:0.5). Then dried plates are sprayed with 1% vanillin-sulphuric acid or anisaldehyde sulphuric acid and heat plates for 10 minutes at 110°C. The purplish spot of the isolated compound i.e. glycyrrhetinic acid has an Rf value of 0.41.

Glycyrrhetinic acid
Fig.1: Glycyrrhetinic acid

Identification Test

  1. Liebermann test- 2 ml test extract is mixed with 2 ml acetic anhydride. Boil the solution and add 0.5 ml of sulphuric acid which will develop blue colour.
  2. Liebermann Burchard test- 2 ml test extract is mixed with 1 ml chloroform and 1 ml acetic anhydride. Then add one drop of concentrated sulphuric acid. Blue-green to red-orange colour develops.
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