Tetracycline Antibiotics - Essay Example

Structure and Mode of Action of Tetracycline Antibiotics Tetracycline antibiotics were obtained after systematic screening of soil samples from all parts of the world for microorganisms capable of producing antibiotic substances (Goodman & Gilman, 2001). Chlortetracycline was the first compound from this class which was successfully used to treat diseases of bacterial origin. They are one of the most widely used classes of antibiotics today and several thousand of varieties have been synthesized till date (Aleksandrov & Simonson, 2008).

They are broad spectrum in action and are effective against a number of gram-positive, gram-negative bacteria, rickettsiae and Chlamydia. Chlortetracycline and Oxytetracycline are obtained from Streptomyces aureofaciens and Streptomyces rimosus respectively (Goodman & Gilman, 2001). Other semi synthetic tetracyclines are Tetracycline, Methacycline, Doxycycline and Minocycline. All tetracyclines are congeners of polycyclic naphthacenecarboxamide and chemical substituents and their position determine the type of tetracycline (Goodman & Gilman, 2001).

Chemically Tetracyclines are polyketides and comprise of a naphthacene ring structure (Thiele-Bruhn, 2003). They are amphoteric compounds and are relatively stable in acids. They are sparingly water soluble while the solubility of corresponding hydrochlorides is much higher. They strongly absorb light and are therefore subject to photodegradation. CONGENER SUBSTITUENT (S) POSITION (S) CHLORTETRACYCLINE -Cl (7) OXYTETRACYCLINE -OH,-H (5) DEMECLOCYCLINE -OH,-H;-Cl (6;7) METHACYCLINE -OH,-H;=CH2 (5;6) DOXYXYCLINE -OH,-H;-CH3,-H (5;6) MINOCYCLINE -H,-H;-N(CH3)2 (6;7) STRUCTURAL FORMULAS OF TETRACYCLINES (Table from: Goodman & Gilman, 2001) Tetracyclines are basically bactericidal in action and do so by inhibiting bacterial protein synthesis (Goodman & Gilman, 2001).

They do so by binding to the 30 S bacterial ribosome, thereby preventing access of aminoacyl tRNA to the acceptor site on the mRNA-ribosome complex. The active transport system found in the bacterial cells enhances the passage of the tetracyclines into them by the process of passive diffusion through the hydrophilic channels. References: Aleksandrov Alexey & Simonson Thomas, (2008), Molecular Mechanics Models for Tetracycline Analogs, J Comput Chem 30: 243–255 Goodman & Gilmans The Pharmacological Basis of Therapeutics, (2001), Tenth Edition, Chapter 47, Antimicrobial Agents (Continued), Pgs 1240-1241, McGraw-Hill Thiele-Bruhn Soren, (2003), Pharmaceutical antibiotic compounds in soils - a review, J.

Plant Nutr. Soil Sci., 166, 145-167 Picture courtesy: Antibiotiques: Online article available at: http://membres.lycos.fr/jjww/antibiotiques.htm