4-GLYCOSIDES__1_

GLYCOSIDES

Definition

  • Glycosides: Compounds that yield one or more sugars upon hydrolysis.

    • Composed of two components: a non-sugar part (genin) and a sugar part (glycone).

    • The two components are linked via a glycosidic linkage.

Classification and Distribution

  • Glycosides can be classified based on different criteria:

    • On the Basis of Glycone:

      • Glucoside (e.g., derived from glucose)

      • Fructoside (e.g., derived from fructose)

    • On the Basis of Glycosidic Linkage:

      • O-Glycosides (alcoholic or phenolic aglycones)

      • S-Glycosides (sulfur-containing compounds)

      • N-Glycosides (containing nitrogen)

      • C-Glycosides (formed with a C-glycosidic bond)

Physicochemical Properties

  • Physical Properties:

    • Most glycosides are soluble in water and alcohol.

    • Typically insoluble in non-polar solvents.

    • Colorless, non-volatile, and often bitter; exceptions exist (e.g., glycyrrhiza).

  • Chemical Properties:

    • Do not reduce Fehling's solution.

    • Hydrolyzed to yield reducing sugars (except for C-glycosides).

Importance

  • In Plants:

    • Serve regulatory, protective, and sanitary functions.

    • Function in processes like pollination and act as sugar reservoirs.

  • Therapeutic Effects in Humans/Animals:

    • Cardiac Drugs: Cardiotonic glycosides (e.g., digitalis)

    • Laxatives: Hydrolyzed forms from plants such as senna and rhubarb.

    • Anti-inflammatory: Certain glycosides such as glycyrrhizin.

Biosynthesis

  • Involves two parts:

    1. Transfer of a uridyl group from UTP to a sugar-1-P catalyzed by uridyl transferase.

    2. Transfer of the sugar from UDP to an acceptor (aglycone), mediated by glycosyl transferase.

Classification Based on Aglycone Structure

  • Cardioactive Glycosides: e.g. Digitoxin

  • Anthraquinone Glycosides: e.g. Chrysophanol, sennosides

  • Saponin Glycosides: e.g. Dioscin

  • Cyanogenic Glycosides: e.g. Amygdalin

  • Isothiocyanate Glycosides: e.g. Sinigrin

  • Flavonoid Glycosides: e.g. Quercitrin

  • Alcohol Glycosides: e.g. Salicin

  • Aldehyde Glycosides: e.g. Glucovanillin

Pharmacological Properties

  • Cardiac Glycosides:

    • Steroidal compounds impacting cardiac muscle contractility.

  • Anti-Inflammatory: Some glycosides like glycyrrhizin exhibit demulcent properties.

  • Medicinal Importance: Glycosides serve various therapeutic roles, such as in the treatment of hypertension and other cardiovascular issues.

Testing and Identification

  • Chemical Tests:

    • Keller-Kiliani test for deoxy sugars.

    • Liebermann’s test for steroid detection.

  • Physical Properties:

    • Solubility varies based on the number of sugar units linked, affecting extraction and therapeutic efficacy.