Page 51 - Pharmd general phytochemistry I-Final2024_LEUCTERS

# If the solution shows gradual increase in the optical rotation till
equilibrium β-glycoside

Physical and chemical properties of glycosides:

• Most glycosides are soluble in water, alcohol and in diluted
alcohol, but they are either less soluble or Insoluble in non-polar
organic solvents.

The higher the number of sugar units, the glycosides will be more
soluble in polar solvents and less soluble in non polar solvent

• Glycosides give +ve results with Molisch's R.

• Glycosides don’t themselves reduce Fehling’s solution, but they
are all susceptible to hydrolysis with the liberation of reducing
sugars (which can reduce Fehling’s solution).
I.e. Glycosides give + ve resultes with Fehling’s solution only
after hydrolysis.

Qualitative tests

(1)- Tests depend on the chemical nature of the Genin:

- Steroidal or cardiac glycosides +ve Libermann’s test.

- Anthraquinone glycosides reddish color with alkalis.

- Flavonoidal glycosides yellow color with alkalis, AlCl3,FeCl3,…

Thio-glycosides black precipitate with silver nitrate.

Cyanogenetic glycosides: give upon hydrolysis HCN, which can be easily tested
for by Guignard,s test (sodium picrate paper)

(2)- Tests depend on the Sugar part :

Some Cardiac glycosides contain 2-deoxysugars, which can be tested
by Keller-Kiliani’s test.

The specific action of the hydrolyzing enzymes is often applied for the
identification of the sugar moieties or even for identification of the
glycoside as a whole.

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