Chemical Tests of Glycosides

CHEMICAL TESTS OF GLYCOSIDES

Glycosides are the compounds with organic molecules having attached glucose or any mono-oligo saccharide unit. Usually, these are crystalline or amorphous solids; opti-cally active, soluble in water and alcohol but insoluble in organic solvents like ether, chloroform and benzene etc. Generally, aqueous or alcoholic extracts of crude drugs are tested with specific reagents for presence of various types of glycosides.

Chemical Tests for Anthraquinone Glycosides

Borntrager’s test

To 1 gm of drug add 5–10 ml of dilute HCl boil on water bath for 10 min and filter. Filtrate was extracted with CCl₄/ benzene and add equal amount of ammonia solution to fil trate and shake. Formation of pink or red colour in ammoni-cal layer due to presence of anthraquinone moiety.

Modified borntrager’s test

To 1 gm of drug, add 5 ml dilute HCl followed by 5 ml ferric Chloride (5% w/v). Boil for 10 min on water bath, cool and filter, filtrate was extracted with carbon tetra-chloride or benzene and add equal volume of ammonia solution, formation of pink to red colour due to presence of anthraquinone moiety. This is used C-type of anthraqui-none glycosides.

Chemical Tests for Saponin Glycosides

Haemolysis test

A drop blood on slide was mixed with few drops of aq. Saponin solution, RBC’s becomes ruptured in presence of saponins.

Foam test

To 1 gm of drug add 10–20 ml of water, shake for few minutes, formation frothing which persists for 60–120 s in presence of saponins.

Chemical Tests for Steroid and Triterpenoid Glycosides

Libermann burchard test

Alcoholic extract of drug was evaporated to dryness and extracted with CHCl₃, add few drops of acetic anhydride followed by conc. H₂ SO₄ from side wall of test tube to the CHCl₃ extract. Formation of violet to blue coloured ring at the junction of two liquid, indicate the presence of steroid moiety.

Salkowaski test

Alcoholic extract of drug was evaporated to dryness and extracted with CHCl₃, add conc. H₂ SO₄ from sidewall of test tube to the CHCl₃ extract. Formation of yellow coloured ring at the junction of two liquid, which turns red after 2 min, indicate the presence of steroid moiety.

Antimony trichloride test

Alcoholic extract of drug was evaporated to dryness and extracted with CHCl₃, add saturated solution of SbCl₃ in CHCl₃ containing 20% acetic anhydride. Formation of pink colour on heating indicates presence of steroids and triterpenoids.

Trichloro acetic acid test

Triterpenes on addition of saturated solution of trichloro acetic acid forms coloured precipitate.

Tetranitro methane test

It forms yellow colour with unsaturated steroids and trit-erpenes.

Zimmermann test

Meta dinitrobenzene solution was added to the alcoholic solution of drug containing alkali, on heating it forms violet colour in presence of keto steroid.

Chemical Tests for Cardiac Glycosides

Keller-kiliani test

To the alcoholic extract of drug equal volume of water and 0.5 ml of strong lead acetate solution was added, shaked and filtered. Filtrate was extracted with equal volume of chloroform. Chloroform extract was evaporated to dryness and residue was dissolved in 3 ml of glacial acetic acid followed by addition of few drops of FeCl₃ solution. The resultant solution was transferred to a test tube contain-ing 2 ml of conc. H₂SO₄. Reddish brown layer is formed, which turns bluish green after standing due to presence of digitoxose.

Legal test

To the alcoholic extract of drug equal volume of water and 0.5 ml of strong lead acetate solution was added, shaked and filtered. Filtrate was extracted with equal volume of chloroform and the chloroform extract was evaporated to dryness. The residue was dissolved in 2 ml of pyridine and sodium nitropruside 2 ml was added followed by addition of NaOH solution to make alkaline. Formation of pink colour in presence of glycosides or aglycon moiety.

Baljet test

Thick section of leaf of digitalis or the part of drug con-taining cardiac glycoside, when dipped in sodium picrate solution, it forms yellow to orange colour in presence of aglycones or glycosides.

 3,5-dinitro benzoic acid test

To the alcoholic solution of drug few drops of NaOH followed by 2% solution of 3,5-dinitro benzoic acid was added. Formation of pink colour indicates presence of cardiac glycosides.

Chemical Tests for Coumarin Glycosides

FeCl₃ test

To the concentrated alcoholic extract of drug few drops of alcoholic FeCl₃ solution was added. Formation of deep green colour, which turned yellow on addition of conc. HNO₃, indicates presence of coumarins.

Fluorescence test

The alcoholic extract of drug was mixed with 1N NaOH solution (one ml each). Development of blue-green fluo-rescence indicates presence of coumarins.

Chemical Tests for Cynophoric Glycoside

Sodium picrate test

Powdered drug was moistened with water in a conical flask and few drops of conc. Sulphuric acid was added. Filter paper impregnated with sodium picrate solution followed by sodium carbonate solution was trapped on the neck of flask using cork. Formation of brick red colour due to volatile HCN in presence of cynophoric glycosides takes place.

Chemical Tests for Flavonoid Glycosides

Ammonia test

Filter paper dipped in alcoholic solution of drug was exposed to ammonia vapor. Formation of yellow spot on filter paper.

Shinoda test

To the alcoholic extract of drug magnesium turning and dil. HCl was added, formation of red colour indicates the presence of flavonoids. To the alcoholic extract of drug zinc turning and dil. HCl was added, formation of deep red to magenta colour indicates the presence of dihydro flavonoids.

Vanillin HCl test

Vanillin HCl was added to the alcoholic solution of drug, formation of pink colour due to presence of flavonoids.