Penam

Chemical Compound
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References

Benzylpenicillin, an example of a penam

Penams represent the structural core of the penicillin subclass of β-lactam antibiotics. They are bicyclic compounds characterized by a β-lactam ring fused to a five-member thiazolidine ring. The penam skeleton is integral to the activity of these antibiotics, which disrupt bacterial cell wall synthesis.

Structure and Properties

The penam structure consists of:

• A β-lactam ring: A four-membered cyclic amide responsible for antibacterial activity.
• A thiazolidine ring: A sulfur-containing five-membered ring fused to the β-lactam ring.

Penams exhibit:

• High strain energy: The 90º bond angles in the β-lactam ring deviate significantly from the ideal sp² or sp³ bond angles, causing angle strain.
• Limited resonance stabilization: The amide bond between the β-lactam carbonyl group and nitrogen is distorted, reducing overlap between lone pair and π orbitals.

These features make penams highly reactive, especially to β-lactamase enzymes and acidic or basic conditions.

Biological Significance

Penams are critical components of penicillin antibiotics, which target the bacterial cell wall. Their mode of action involves:

• 1. Binding to penicillin-binding proteins (PBPs) in bacteria.
• 2. Inhibiting the final steps of peptidoglycan synthesis, weakening the cell wall.
• 3. Inducing bacterial cell lysis.

Examples of penam antibiotics include:

• Benzylpenicillin (penicillin G)
• Phenoxymethylpenicillin (penicillin V)

Chemical Reactivity

Penams are susceptible to hydrolysis by β-lactamases, enzymes produced by resistant bacteria. This reaction cleaves the β-lactam ring, rendering the antibiotic inactive. To counteract this, β-lactamase inhibitors such as clavulanic acid are used in combination therapies.

Applications

Penams are used in the treatment of:

• Bacterial infections such as streptococcal pharyngitis, syphilis, and endocarditis.
• Conditions caused by penicillin-sensitive organisms.

Related Compounds

Penams are part of a broader family of β-lactam antibiotics, which includes:

• Penems
• Carbapenems
• Cephalosporins

See Also

• Antibiotic resistance
• Penicillin-binding protein
• β-lactamase inhibitors
• Sulbactam
• Tazobactam

External Links

• Penicillin Mechanisms - PubMed
• Penam Studies on ScienceDirect