Glycosides

GGlycosides

Glycosides are compounds formed from a simple sugar and another compound by replacement of a hydroxyl group in the sugar molecule. Many drugs and poisons derived from plants are glycosides.
Glycosides =
– aglycone / ‘genin’ - hydrocarbon part
– glycone - sugar part (water solubility)

• more important in medicine than a lot of drugs
• occur in higher plant tissues in very small amounts
• also fungal and bacterial cells (exuded in medium) and animals


Inside the body the glycoside will be cleaved to glycone and aglycone parts. The glycone part confers on the molecule solubility properties , thus is important in the absorption and distribution in the body , while the aglycone part is responsible for the pharmacological activity. All glycosides are hydrolyzed by boiling with mineral acid , on the other hand the presence of specific enzyme in the plant tissue , but in deferent cells from those that contain the glycosides , are able to hydrolyzed the glycosides.

Classification
1- Atom from the aglycone involved in the glycosidic linkage:
Aglycone- O- Sugar O-glycosides
Aglycone- C- Sugar C-glycosides
Aglycone- S- Sugar S-glycosides
Aglycone- N- Sugar N-glycosides
2- Number of sugars:
One sugar monosides e.g. Salicin.
Two sugar Biosides e.g. Diosmin.
Three sugars Triosides e.g. Digoxin.
3- Botanical source:
example:
Digitalis glycosides
Senna glycosides.
4- Therapeutic use:
example:
Analgesic glycosides.
Purgative glycosides.
Cardiac glycosides.
5- Chemical nature of the aglycone:
example:
Flavone glycosides.
Steroidal glycosides.
Aldehydic glycosides.

Nature of the glycoside:
1- Primary glycosides: Originally present in the plant e.g. Purpurea A
2- Secondary glycosides: Resulted from removal of one sugar from the primary glycosides e.g. Digitoxin

Extraction
• most quite polar – due to phenols and sugars
• water|alcohol or mixtures of them used
• dried plant material percolation in industrial columns with dilute alcohol
• tincture produced . partitioned with chloroform|ether to clean up (remove green pigment, fats, lipids)
• clean yellow tincture subjected to column chromatography
• crystallised for purity