Macrolides

Historical Background of Macrolides

• First discovered in 1952 (Erythromycin from Saccharopolyspora erythraea).
• Used for respiratory infections and atypical bacteria.

Nomenclature of Macrolides

• Named after the macrocyclic lactone ring.
• Examples:
  • Erythromycin
  • Clarithromycin
  • Azithromycin

Stereochemistry

• 14-, 15-, or 16-membered lactone rings.
• Various sugar moieties (e.g., desosamine, cladinose).

Structure-Activity Relationship (SAR)

• Lactone ring size: Affects ribosomal binding.
• Sugar modifications:
  • Improve acid stability (Clarithromycin, Azithromycin).
  • Enhance bioavailability.
• C-9 modifications: Affect efflux pump resistance.

Chemical Degradation Classification

• Acid instability: Leads to inactive ketal products (Erythromycin).
• Hydrolysis of lactone ring.
• Oxidative degradation.

Important Products

• Erythromycin (first macrolide).
• Clarithromycin (acid-stable, better absorption).
• Azithromycin (long half-life, broad spectrum).
• Roxithromycin (enhanced tissue penetration).

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