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Renin Angiotensin Mechanism.

Lecture note on Glycosides

Lecture note on "Glycosides".

  • Glycosides are the compounds of plant and animal origin which on hydrolysis yields a sugar compound (glycone) and a nonsugar compound (aglycone), having marked physiological actions.

  • Common sugars found in glycosides are glucose, mannose, rhamnose, & digitoxose.

  • The common non- sugar part is alcohol/ phenol/ amine.

  • The activity of glycoside is due to non-sugar part (aglycone).

  • Glycone part plays role in pharmacokinetic properties of the glycoside like, absorption, metabolism, distribution and excretion..

·         Physical Properties:


  • Glycosides are crystalline colorless solids.
  •  Non- reducing in nature and are generally laevorotatory.
  •  They are soluble in alcohol & water.
  •  Dilute acids and enzymes cause their hydrolysis.

·         Biological role: -


  • They protect the plant from insects & animals.
  •  They stimulate growth, reproduction & metabolism of the plant.
  •  Glycosides act as a storage of chemicals for many plants.


Classification: - Glycosides can be classified by two methods



  • 1.      According to the basis of chemical nature of Aglycone.

  • 2.      According to the chemical linkage between Glycone & Aglycone.


 A) Classification according to the chemical nature of Aglycone: -


·         1) Cyanophoric or cyanogenic glycosides: -


  • This type of glycoside produces one molecule of Hydrocyanic acid (HCN) & sugar on hydrolysis.
  •   e. g. Amygdaline in bitter almond.

·         2) Cardiac Glycoside: -

  •  This type of glycoside acts on heart muscle they increase the force of contraction of the heart.

  •  Cardiac glycosides are again divided into Cardenolides (C23)  & Bufadienolides (C24)
  •  e.g. Purpurea glycosides in digitalis leaf.

·         3) Isothiocyanate glycosides: -


  • These glycosides give one molecule of sulfur on hydrolysis.
  •  e. g. sinigrin in black mustard

·         4) Saponins: -


  • These on hydrolysis gives aglycone known as sapogenin.
  • They form soapy, a colloidal solution with water.
  •  They cause breakdown of R. B. Cs (hemolysis) in very low concentration.
  •  Saponins are good detergents & emulsifying agents.
  •  e. g. Digitonin, gitonin in digitalis leaf.

·         5) Phenolic Glycosides: -


  • According to chemical nature, these glycosides are divided into following types:

Type
Aglycone
Source
Simple Phenolic glycoside
Salicin
Salix species
Anthraquinone glycosides
Barbaloin, aloe- emodin
Aloe, Rhubarb, Senna
Coumarin glycosides
Umbelliferone
Asafoetida, Tobacco
Flavone & flavonoid
Gentisin, Kaempferol
Senna, Gentian, Liquorice
Anthocyanidine
Cyanidin, Malvidin
Rose, Purple grapes.

B) Classification according to the chemical linkage between glycone & Aglycone:

·         1) O-glycosides: -


·         If the glycoside sugar combines with OH group of the non- sugar part.

·         e.g R – HO + OH C6 H11 O5   ------>  -O C6 H11 O5  (e. g Cardiac glycosides.)

·         2) C – Glycosides: -


·         In this type, the carbon atom from aglycone combines with sugar.

·         e.g R – CH + OH C6 H11 06 = -C-C6 H11  (e. g. Aloin in Aloe)

·         3) S- Glycoside: -


·         In this type, the sulfur atom from aglycone combines with sugar.

·         R – SH + OH + C6 H11 O5 = -S – C6 H11 O5 (e. g Isothiocyanate glycoside that is sinigrin)

·         4) N – Glycosides: -


·         In this type nitrogen from aglycone combines with sugar.

·         > N – H + OH C6 H11 O5 = > -N – C6 H11 O5 e. g. Nucleosides.


Isolation of Glycosides: -

1.      Extract the powdered drug with water or alcohol.

2.      Due to this, enzymes present in the tissues get destroyed.

3.      Add lead acetate solution to precipitate impurities present in the drug sample.

4.      Filter the solution & pass H2S gas through filtrate to neutralize excess of lead.

5.      Now concentrate the extract to get crude product.

      Purify the product by using chromatography techniques.
Identification tests for Glycosides:-
1)        Test for Anthraquinone glycoside: Bontrager's Test.

2)       Test for cardiac glycoside Write keller killiani test of digitalis.

3)       Test for saponins.


1.         Test for saponins are –

A)        Shake the powdered drug with water to form soapy solution

B)         If powdered drug is added to the sample of blood it causes breaking of R.B.Cs (hemolysis).

2. Test for Anthraquinone Glycosides:

A) Borntrager's Test:



B) Modified Borntrager's Test:



C) Keller Killani Test for Cardiac Glycosides:


D) Other Chemical tests for glycosides:



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