Tetracyclines have the broadest spectrum of antimicrobial
activity. These may include: Aureomycin, Terramycin, and Panmycin.
Four fused 6-membered rings, as shown in the figure below,
form the basic structure from which the various tetracyclines
are made. The various derivatives are different at one or more
of four sites on the rigid, planar ring structure. The classical
tetracyclines were derived from Streptomyces spp., but the newer
derivatives are semisynthetic as is generally true for newer
members of other drug groups.
Mechanism of Action:
Tetracyclines inhibit bacterial protein synthesis by blocking
the attachment of the transfer RNA-amino acid to the ribosome.
More precisely they are inhibitors of the codon-anticodon interaction.
Tetracyclines can also inhibit protein synthesis in the host,
but are less likely to reach the concentration required because
eukaryotic cells do not have a tetracycline uptake mechanism.