Glycosides are the compounds with organic molecules having attached glucose or any mono-oligo saccharide unit. Usually, these are crystalline or amorphous solids; optically active, soluble in water and alcohol but insoluble in organic solvents like ether, chloroform and benzene etc.
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.
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