Write short notes on glycosides.

Glycosides are the acetal derivatives of monosaccharide with an alcohol which is formed in the presence of an acid catalyst. Glycosides are stable to alkaline oxidants such as Tollen’s reagent, but, hydrolysed back to their alcohol and sugar components by aqueous acid. The anomeric methyl glycosides are formed in an equilibrium ratio of 66% alpha to 34% beta. Pyranose rings prefer chair conformations with equatorial substituents and β-glucose only has all the substituents on equatorial while in α-isomer substituents are in axial. The preference for alpha-glycopyranoside formation in spite of the stability is referred to as the anomeric effect.

Physical properties

  • Glycosides are crystalline colourless solids
  • They are soluble both in alcohol & water.
  • Dilute acids and enzymes cause their hydrolysis.

Identification tests for Glycosides

1)        Test for Anthraquinone glycoside: Bontrager’s Test.
2)       Test for cardiac glycoside Write Keller Killian test of digitalis.

 

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