{{Short description|Cyclic amide}} [[Image:Lactams.svg|thumb|right|450px|From left to right, the above are general structures of β-lactam, a γ-lactam, a δ-lactam, and ε-lactam. Their common names are β-propiolactam, γ-butyrolactam, δ-valerolactam, and ε-caprolactam.]]
A '''lactam''' is a cyclic amide, formally derived from an amino carboxylic acid through cyclization reactions.<ref>{{GoldBookRef|title=Lactams|file=L03435}}</ref> The term is a portmanteau of the words ''lactone'' + ''amide''.
==Nomenclature== Greek prefixes in alphabetical order indicate ring size.
{| {{table}} ! Ring size<br />(number of atoms in the ring) ! {{nobr|Systematic name}} ! IUPAC name ! {{nobr|Common name}}(s) ! Structure |- |3 |α-Lactam |Aziridin-2-one |α-Acetolactam |100px |- |4 |β-Lactam |Azetidin-2-one |β-Propiolactam |100px |- |5 |γ-Lactam |Pyrrolidin-2-one |{{ubl|γ-Butyrolactam|2-Pyrrolidone}} |100px |- |6 |δ-Lactam |Piperidin-2-one |{{ubl|δ-Valerolactam|2-Piperidinone|2-piperidone}} |100px |- |7 |ε-Lactam |Azepan-2-one |{{ubl|ε-Caprolactam|Caprolactam}} |100px |}
This ring-size nomenclature stems from the fact that hydrolysis of an α-lactam gives an α-amino acid and that of a β-Lactam gives a β-amino acid, and so on.
==Synthesis==<!-- This section is linked from Organic reaction --> General synthetic methods are used for the organic synthesis of lactams.
===Beckmann rearrangement=== Lactams form by the acid-catalyzed rearrangement of oximes in the Beckmann rearrangement.
===Schmidt reaction=== Lactams form from cyclic ketones and hydrazoic acid in the Schmidt reaction. Cyclohexanone with hydrazoic acid, forms ε - Caprolactam, which upon treatment with excess acid forms Cardiazole, a heart stimulant.
===Cyclization of amino acids=== Lactams can be formed from cyclisation of amino acids via the coupling between an amine and a carboxylic acid within the same molecule. Lactamization is most efficient in this way if the product is a γ-lactam. For example, Fmoc-Dab(Mtt)-OH, although its side-chain amine is sterically protected by extremely bulky 4-Methyltrityl (Mtt) group, the amine can still intramolecularly couple with the carboxylic acid to form a γ-lactam. This reaction almost finished within 5 minutes with many coupling reagents (e.g. HATU and PyAOP).<ref>{{cite journal |last1=Lam |first1=Pak-Lun |last2=Wu |first2=Yue |last3=Wong |first3=Ka-Leung |title=Incorporation of Fmoc-Dab(Mtt)-OH during solid-phase peptide synthesis: a word of caution |journal=Organic & Biomolecular Chemistry |date=30 March 2022 |volume=20 |issue=13 |pages=2601–2604 |doi=10.1039/D2OB00070A |pmid=35258068 |s2cid=247175352 |url=https://pubs.rsc.org/en/content/articlelanding/2022/ob/d2ob00070a |language=en |issn=1477-0539|url-access=subscription }}</ref>
===Intramolecular nucleophilic substitution=== Lactams form from intramolecular attack of linear acyl derivatives from the nucleophilic abstraction reaction.
===Iodolactamization=== An iminium ion reacts with a halonium ion formed in situ by reaction of an alkene with iodine.<ref>Spencer Knapp, Frank S. Gibson Organic Syntheses, Coll. Vol. 9, p.516 ('''1998'''); Vol. 70, p.101 ('''1992''') [http://orgsynth.org/orgsyn/prep.asp?prep=cv9p0516 Online article]</ref> :700px|Iodolactamization reaction
===Kinugasa reaction=== Lactams form by copper-catalyzed 1,3-dipolar cycloaddition of alkynes and nitrones in the Kinugasa reaction
===Diels-Alder reaction=== Diels-Alder reaction between cyclopentadiene and chlorosulfonyl isocyanate (CSI) can be utilized to obtain both β- as well as γ-lactam. At lower temp (−78 °C), β-lactam is the preferred product. At optimum temperatures, a highly useful γ-lactam known as Vince Lactam<ref>Singh, R.; Vince, R. ''Chem. Rev.'' '''2012,''' ''112 (8),'' pp 4642–4686."2-Azabicyclo[2.2.1]hept-5-en-3-one: Chemical Profile of a Versatile Synthetic Building Block and its Impact on the Development of Therapeutics"</ref> is obtained.<ref>Pham, P.-T.; Vince, R. ''Phosphorus, Sulphur and Silicon'' '''2007''', 779-791.</ref> :400px|Preparation of VL and beta lactam
==Lactam–lactim tautomerism== A '''lactim''' is a cyclic imidic acid compound characterized by an endocyclic carbon-nitrogen double bond. They are formed when lactams undergo tautomerization.
:thumb|320px| Lactam Lactim
==Reactions==<!-- This section is linked from Organic reaction --> * Lactams can polymerize to polyamides.
== See also == * Lactone, a cyclic ester. * β-Lactam * β-Lactam antibiotics, which includes penicillins * 2-Pyrrolidone * 2-Piperidinone * Caprolactam
==References== {{Reflist}}
==External links== *{{Commons category-inline|Lactams}}
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Category:Functional groups Category:Lactams