Penam

Penam
Names
	IUPAC name (5R)-4-thia-1-azabicyclo[3.2.0]heptan-7-one
	Other names 1-Aza-7-oxo-4-thiabicyclo[3.2.0]heptane
Identifiers
CAS Number	53908-04-6 [ChemSpider];
3D model (JSmol)	Interactive image;
Beilstein Reference	4374479
ChEBI	CHEBI:35991 ;
ChemSpider	7827765;
PubChem CID	9548842;
	InChI InChI=1S/C5H7NOS/c7-4-3-5-6(4)1-2-8-5/h5H,1-3H2/t5-/m1/s1 Key: WSHJJCPTKWSMRR-RXMQYKEDSA-N; InChI=1S/C5H7NOS/c7-4-3-5-6(4)1-2-8-5/h5H,1-3H2/t5-/m1/s1 Key: WSHJJCPTKWSMRR-RXMQYKEDSA-N;
	SMILES C1CSC2N1C(=O)C2;
Properties
Chemical formula	C5H7NOS
Molar mass	129.18 g·mol−1
Related compounds
Related compounds	clavam
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Penams are bicyclic ring systems containing a β-lactam moiety fused with a five-member thiazolidine ring. The parent penem, which is only of pedagogical interest, has the formula CHSCHCH₂CH₂NC(O)CH₂. Substituted derivatives are of great interest because they include the penicillins. Due to ring strain and limitations on amide resonance, the structure is susceptible to catalytic cleavage at the amide bond. Benzylpenicillin (penicillin G) is a naturally occurring penam.

The IUPAC Nomenclature of Organic Chemistry lists penam among parent structures of natural compounds, being the single enantiomer (R).

Structure

Penams are relatively inflexible. The structure is locked in a puckered (i.e. bent) shape. The bridgehead nitrogen is somewhat pyramidal (χ = 54°), in contrast to acyclic amides. The C-N bond (τ = 18°) is twisted. The amide C-N bond length is 1.406 Å and displays greater single bond character than in noncyclic tertiary amides. The C-O bond length is 1.205 Å which is shorter than C-O bonds in noncyclic tertiary amides. Consequently, penams are susceptible to acid- and base-catalyzed hydrolysis.

References

1 2 Singh, Girija S.; Sudheesh, Siji (2013). "β-Lactams". Natural Lactones and Lactams. pp. 101–145. doi:10.1002/9783527666911.ch3. ISBN 978-3-527-33414-8.
↑ Patrick, Graham (2017-03-23), "5. Pharmaceuticals and medicinal chemistry", Organic Chemistry: A Very Short Introduction, Oxford University Press, pp. 71–89, doi:10.1093/actrade/9780198759775.003.0005, ISBN 978-0-19-875977-5
↑ "Nomenclature of Organic Chemistry. IUPAC Recommendations and Preferred Names 2013. Appendix 3. STRUCTURES FOR ALKALOIDS, STEROIDS, TERPENOIDS, AND SIMILAR COMPOUNDSBlue Book Appendix 3". iupac.qmul.ac.uk. Retrieved 23 October 2026.
1 2 Glover, Stephen A.; Rosser, Adam A. (2012-06-14). "Reliable Determination of Amidicity in Acyclic Amides and Lactams". The Journal of Organic Chemistry. 77 (13): 5492–5502. doi:10.1021/jo300347k. ISSN 0022-3263. PMID 22646836.
1 2 Hu, Feng; Lalancette, Roger; Szostak, Michal (2016-03-08). "Structural Characterization of N-Alkylated Twisted Amides: Consequences for Amide Bond Resonance and N−C Cleavage". Angewandte Chemie International Edition. 55 (16): 5062–5066. Bibcode:2016ACIE...55.5062H. doi:10.1002/anie.201600919. ISSN 1433-7851. PMID 26953809.

[:0-1] 1 2 Singh, Girija S.; Sudheesh, Siji (2013). "β-Lactams". Natural Lactones and Lactams. pp. 101–145. doi:10.1002/9783527666911.ch3. ISBN 978-3-527-33414-8.

[:1-2] Patrick, Graham (2017-03-23), "5. Pharmaceuticals and medicinal chemistry", Organic Chemistry: A Very Short Introduction, Oxford University Press, pp. 71–89, doi:10.1093/actrade/9780198759775.003.0005, ISBN 978-0-19-875977-5

[3] "Nomenclature of Organic Chemistry. IUPAC Recommendations and Preferred Names 2013. Appendix 3. STRUCTURES FOR ALKALOIDS, STEROIDS, TERPENOIDS, AND SIMILAR COMPOUNDSBlue Book Appendix 3". iupac.qmul.ac.uk. Retrieved 23 October 2026.

[:2-4] 1 2 Glover, Stephen A.; Rosser, Adam A. (2012-06-14). "Reliable Determination of Amidicity in Acyclic Amides and Lactams". The Journal of Organic Chemistry. 77 (13): 5492–5502. doi:10.1021/jo300347k. ISSN 0022-3263. PMID 22646836.

[:3-5] 1 2 Hu, Feng; Lalancette, Roger; Szostak, Michal (2016-03-08). "Structural Characterization of N-Alkylated Twisted Amides: Consequences for Amide Bond Resonance and N−C Cleavage". Angewandte Chemie International Edition. 55 (16): 5062–5066. Bibcode:2016ACIE...55.5062H. doi:10.1002/anie.201600919. ISSN 1433-7851. PMID 26953809.