Penem

A penem is a type of β-lactam with an unsaturated five-member heterocycle containing a sulfur atom fused to the β-lactam ring. Penems do not occur naturally; all are synthetic.[1] Related to penems are carbapenems, which have a carbon atom in place of the sulfur atom.[2]

An example is faropenem.[3]

Structure
Faropenem, a penem. Note sulfur and double bond in ring.
Imipenem, a carbapenem. Although imipenem has a sulfur, the sulfur is not in the ring.
Benzylpenicillin, a Penicllin. Note the absence of the double bond in the ring.

Penem molecules do not occur naturally, and production of penems is an entirely synthetic process.

Five main penem subgroups — thiopenems, oxypenems, aminopenems, alkylpenems, and arylpenems — have been produced and are distinguished by the side chain (at position 2) of the unsaturated five-membered ring. One structurally distinct penem is BRL 42715. This molecule has no substitution at the above position, but has a bulky group attached to the β-lactam ring, and it displays effective inhibition of class C β-lactamases, but no antimicrobial activity.

One possible consequence of these structural differences of penems from other β-lactams may be reduced immunogenicity and immunogenic cross-reactivity.

References
  1. Richard Wise (1990). "The carbapenems and Penem Antibiotics—a brief review". Antimicrobic Newsletter. 7 (10): 73–78. doi:10.1016/0738-1751(90)90045-E.
  2. "Medscape.com".
  3. Milazzo I, Blandino G, Caccamo F, Musumeci R, Nicoletti G, Speciale A (March 2003). "Faropenem, a new oral penem: antibacterial activity against selected anaerobic and fastidious periodontal isolates". Journal of Antimicrobial Chemotherapy. 51 (3): 721–5. doi:10.1093/jac/dkg120. PMID 12615878.

Further reading
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