Glycosides are formed by the interaction of hydroxyl group of non-sugar and sugar with the loss of water molecule. If the sugar is glucose the resulting compound is a glucoside and if it is any other like, mannose, rhamnose, then it is known as a glycoside.
The link between the glycon and aglycon is known as glycosidic linkage.
The therapeutic properties are due to aglycon and sugar simply acts as a carrier.
- They are crystalline, amorphous substances
- Soluble in water
- Insoluble in organic solvents
- They show optical activity
- They are easily hydrolyzed by water and enzymes
- They are bitter to taste
Classification of glycosides
These are the most important glycosides used more extensively in medicine.
- Digitoxin, digoxin, gitoxin are got from fox glove plant or Digitalis purpurea, or Digitalis lanata, the white variety.
- Scillarin A&B are got from Scilla hyacinthine
- These act as cardiac stimulants and cardiac tonics and are used as emergency medicine
- Sennaside A&B produced by Cassia senna and Cassia anguistifolia have laxative effect and are largely exported to cold countries.
- Steroidal saponins are produced by dried tubers of Diascoria and are used as expectorant
- Psoralen is extensively used as a immune modulator in auto-immune skin diseases
- Sinalbin and sinigrin from mustard are used as stimulants
- Hesperidin from citrus fruits is used as an antiseptic
- Rutin from Ruta graveolans is used as a lipid lowering agent
- Salicin is an anti-pyretic and analgesic
- Arbutin is used as an urinary antiseptic
- Amygdalin of bitter almonds has anti-cancer activity
- Gymnemic acid is used in the treatment of diabetes mellitus
Test for glycosides
Drug is powdered and extracted with ether and ammonia or caustic soda. The aques layer shows pink color
This is for cardiac glycosides. chloroform extract of drug and 0.4 glacial acetic acid are mixed with ferrous chloride and 0.5 mi of concentrated sulphuric acid. The acetic acid layer shows blue color.