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A beta-lactam ring (β-lactam) or penam is a lactam with a heteroatomic ring structure, consisting of three carbon atoms and one nitrogen atom 1. A lactam is a cyclic amide.
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Clinical significance
The beta-lactam ring is part of the structure of several antibiotic families, principally the penicillins, cephalosporins, carbapenems and monobactams, which are therefore also called beta-lactam antibiotics. These antibiotics work by inhibiting the bacterial cell wall synthesis. This has a lethal effect on bacteria, especially on Gram-positive ones. Bacteria can become resistant against beta-lactam antibiotics by expressing beta-lactamase.
History
The first synthetic β-lactam ever was prepared by Hermann Staudinger in 1907 by reaction of the Schiff base of aniline and benzaldehyde with diphenylketene 2 3 in a [2+2]cycloaddition:
Beta-lactam resistance
Because of the popularity of beta-lactam drugs, certain bacteria have been able to develop counter-measures to traditional drug therapies. An enzyme called beta-lactamase is present in many different types of bacteria, which serves to 'break' the beta lactam ring, which effectively nullifies the antibiotic's effectiveness.
As a response to bacterial resistance to beta-lactam drugs, there are drugs, such as Augmentin, which are designed to disable the beta-lactamase enzyme. Augmentin is made of amoxicillin, a beta-lactam antibiotic, and clavulanic acid, a beta-lactamase inhibitor. The clavulanic acid is designed to overwhelm all beta-lactamase enzymes, bind irreversibly to them, and effectively serve as an antagonist so that the amoxicillin is not affected by the beta-lactamase enzymes.
Secondary beta-lactam drug resistance
As a response to decreased efficacy of beta-lactamase, some bacteria have changed the proteins that beta-lactam antibiotics bind, the penicillin binding proteins (PBPs). Since the PBPs no longer recognize the beta-lactams, the antibiotics are essentially useless. This is the mechanism behind the methicillin-resistant Staphylococcus aureus (MRSA).
Mechanism
Penicillin, a beta-lactam, binds to and inactivates a bacterium's penicillin binding protein (PBP). PBP's vary in their affinity for binding penicillin or other beta-lactam antibiotics. The amount of PBP's varies between bacterial species. PBP's form transpeptidase bonds in the absence of penicillins or other beta-lactam antimicrobics.
See also
External links
References
- ^ Heterocyclic chemistry T.L. Gilchrist ISBN 0-582-01421-2
- ^ Hugo (Ugo) Schiff, Schiff Bases, and a Century of b-Lactam Synthesis Thomas T. Tidwell Angew. Chem. Int. Ed. 2008, 47, 1016–1020 doi:10.1002/anie.200702965
- ^ H. Staudinger, Justus Liebigs Ann. Chem. 1907, 356, 51 – 123.
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- This page was last modified on 30 December 2008, at 01:26.
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