Page 141 - PG 504-theoretical notes-phyto-1-2024-2025..

Clinical pharmacy PharmD program Third level Phytochemistry-1 (PG-504)

Physical Properties:

• Existence of one or more monosaccharide unit in the glycoside molecules,
make most glycosides are soluble in water, alcohols and dilute alcohols,

• but are either insoluble or less soluble in non-polar organic solvents.

• The higher numbers of sugar units would render the glycoside more soluble in
polar solvents (water, alcohols) and less soluble in non-polar organic solvents

Chemical Reactions:

✓ The reactions due to aglycone:

The characteristic chemical tests for glycosides are due to the aglycone moieties .

✓ The reactions due to sugar part:

• Glycosides themselves do not reduce Fehling’s solution;

• but they are all susceptible to hydrolysis with the liberation of reducing sugars
(except C-glycosides), that reduce Fehling’s solution

• The potential of the glycosides to reduce Fehling's solution is after hydrolysis
due to the release of the sugar part.

❖ So estimation of glycosides is achieved through estimation of reducing sugars
before and after hydrolysis, by boiling with dilute acids or by the action of
specific enzymes

Extraction and Isolation of Glycosides

The most commonly used solvent for extraction is water mixed with different
proportions of methanol (or ethanol).

The methods of isolation of glycosides involves the following steps:

1- Enzymes inactivation (Destruction of the hydrolyzing enzymes):

• Dry heat

• Boiling with water

• Lyophilization

2-Insurance of neutral condition by pH optimization:

Acidic pH may lead to hydrolysis so acidity is neutralized by addition of calcium
carbonate in case of plant rich in acid.

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