Chemistry

• Glycyrrhetinic acid is a pentacyclic triterpenoid, a cyclic terpene ketone, and a hydroxy monocarboxylic acid.

• It is a conjugate acid of a glycyrrhetinate.

• It is derived from a hydride of an oleanane.

• It is olean-12-ene substituted by a hydroxy group at position 3, an oxo group at position 11, and a carboxy group at position 30.

• It is a pentacyclic triterpenoid.

Isolation Methods

Method-1

• From a Glycyrrhizin Salt: In this method, glycyrrhizin is extracted from liquorice root, purified, and then converted to glycyrrhetinic acid.

• There are different forms of this method.

• In one type, concentrated aqueous extract of liquorice root is treated with H2SO4 to precipitate a brown sediment, which is washed with water and extracted with alcohol to isolate glycyrrhizin.

• The extract is added with KOH solution to precipitate the potassium salt of glycyrrhizin, which is filtered and crystallised twice in acetic acid.

• The salt is hydrolysed with H2SO4 to obtain crude glycyrrhetinic acid that is acetylated by acetic anhydride.

• The cake obtained is purified with CHCl3 and CH3OH, and hydrolysed with NaOH solution to obtain white glycyrrhetinic acid.

Method-2

• By Enzymatic Reactions: In this method, glycyrrhetinic acid is produced by the hydrolysis of glycyrrhizin or its salts with aeromonas species or their cultured preparations in the presence of nitrogen, phosphate, and potassium.

• The yield of this method is 91% and the glycyrrhetinic acid obtained has an acceptable purity. However, the method is highly expensive.

Method-3

• By Hydrolysis of Liquorice Root: In this method, glycyrrhizin is hydrolysed directly, i.e., without isolation from liquorice root.

• There are different forms of this method.

• In one type, the liquorice root powder is hydrolysed in tri -chloroacetic acid for 18 hours at 95°C temperature.

• The cooled suspension is neutralised with lime solution and filtered. The cake obtained is washed with water and the released glycyrrhetinic acid is extracted with ethanol.

• The extract is evaporated and residue crystals are crystallised twice in acetic acid to produce glycyrrhetinic acid.

Method-4

• Coarsely powdered drug of Glycyrrhiza is extracted with chloroform.

• The chloroform extract is filtered and filtrate is discarded.

• Then obtained marc is extracted with 0.5M sulphuric acid for few hours.

• Filter it and 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 glycyrhetinic acid.

• Then precipitate is filtered and washed with water upto neutral pH and dried. This will yield glycyrhhetinic acid. Melting point: 300°C.

Thin layer chromatography of Glycyrhetinic acid:

• 1 mg of glycyrhhetinic 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 anisaldehydesulphuric acid and heat plates for 10 minutes at 110°C.

• The purplish spot of isolated compound i.e. glycyrhetinic acid have Rf value 0.41

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