Chemistry: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. Related to penems are carbapenems, which have a carbon atom in place of the sulfur atom.

An example is faropenem.

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.

Further reading

• "Synthetic studies of carbapenem and penem antibiotics. II. Synthesis of 3-acetyl-2-azetidinones by (2 + 2) cycloaddition of diketene and Schiff bases". Chemical & Pharmaceutical Bulletin 40 (5): 1094–7. May 1992. doi:10.1248/cpb.40.1094. PMID 1394625.