Questions
2 questions per paper
Difficulty
Medium
Importance
High yield for B.Pharm pharmacology and pharmacognosy modules
Overview
Glycosides are organic compounds consisting of a sugar moiety (glycone) linked to a non-sugar component (aglycone) via a glycosidic bond. They represent a significant class of secondary metabolites in pharmacognosy with diverse pharmacological actions ranging from cardiotonic to laxative effects. Mastering this topic is essential for understanding plant-based therapeutic agents and their chemical identification.
General Properties and Classification
Glycosides are hydrolyzed by enzymes or acids to release the aglycone and glycone components. Their classification is primarily based on the nature of the aglycone moiety, which determines their specific medicinal activity.
- Linkage involves the hemiacetal hydroxyl group of the sugar.
- Glycosidic bond is typically O-linkage, but C, S, and N-linkages exist.
- Classification categories: Cardiac, Anthraquinone, Saponin, Cyanogenetic, and Flavonoid glycosides.
- Soluble in water and alcohol; insoluble in ether and chloroform.
- Optical rotation is generally levorotatory.
Cardiac Glycosides (Digitalis)
Digitalis contains cardiac glycosides that increase the force of myocardial contraction and decrease heart rate, making them vital for treating congestive heart failure. These are characterized by a steroid nucleus with an unsaturated lactone ring at the C17 position.
- Drug source: Dried leaves of Digitalis purpurea (Foxglove).
- Active constituents: Digoxin, Digitoxin, and Gitoxin.
- Mechanism: Inhibition of Na+/K+ ATPase pump.
- Structural feature: Steroid nucleus fused with a five-membered unsaturated lactone ring.
- Keller-Killiani test is the specific chemical test for deoxy-sugars.
Anthraquinone Glycosides (Senna)
Anthraquinone glycosides exert a purgative effect by increasing peristaltic movement in the large intestine. These compounds are identified by the Borntrager's test, which produces a characteristic pink to red color in an alkaline solution.
- Drug source: Dried leaflets of Cassia angustifolia or Cassia acutifolia.
- Major constituents: Sennosides A and B.
- Mechanism: Stimulation of colon motility via enteric nervous system.
- Identification: Borntrager's test (alkaline pink color).
- Modification: Often standardized by evaluating sennoside content.
Exam Tip
Always prioritize the chemical identification test and the mechanism of action for both Digitalis and Senna, as these are the most frequently asked viva and written exam questions.
Common Mistakes
- Confusing the structural requirement of the five-membered lactone ring in Digitalis with six-membered rings found in other steroids.
- Forgetting to mention the specific chemical tests like Keller-Killiani for Cardiac and Borntrager's for Anthraquinones.
- Incorrectly identifying the glycone vs. aglycone role in therapeutic activity.
More Revision Notes
Ready to test yourself?
Play topic-wise Glycosides questions in Aspirant Arcade — gamified MCQ practice.
Download Free