# Are there amide versions of lactides and lactones?

In my book, I read that Lactides and lactones are cyclic esters which contain two and one ester group in them, respectively. They are formed when $$\alpha$$-hydroxy; and $$\gamma$$- or $$\delta$$- hydroxy carboxylic acids; respectively, are esterified.

Now, there exists a certain similarity between amides and esters (both being carboxylic acid-derivatives), such as the similarity between ester bonds in polyesters and amide bonds in polyamides.

In this context, I have a question: Do amides have compounds similar to lactides and lactones? What are they commonly known as?

Please let me know a good source that I could refer to in addition to any answers posted, or please cite any sources used.

• By the way, there are also lactols. – mykhal Nov 23 '18 at 15:43

Amide analogue of lactons are lactams, their tautomeric forms are lactims. Citing from the IUPAC Nomenclature of Organic Chemistry (Preferred names 2013):

P-66.1.5.1 Lactams and lactims

Intramolecular amides of amino carboxylic acids, $$\ce{-CO-NH\bond{-}}$$, are called ‘lactams’ and their tautomers, $$\ce{-C(OH)=N\bond{-}}$$, are ‘lactims’. Lactams named in two ways:

(1) as heterocyclic pseudoketones;

(2) by substituting ‘lactam’ for the ‘ic acid’ ending of the systematic ‘oic acid’ name for the parent acid without the amino substituent, and inserting a locant designating the position of the amino group between the ‘o’ and the ‘lactam’. Method ‘lactams’. Lactims are named in the same way, using ‘lactim’ in place of ‘lactam’.

(1) generates preferred IUPAC names.

Examples:

pyrrolidin-2-one (PIN)
butano-4-lactam

(…)

3,4,5,6-tetrahydropyridin-2-ol (PIN)
pentano-5-lactim

(Note that the numberings depicted are for the preferred names (PINs) based on nitrogen heterocyclics)

There's no (at least IUPAC) term for lactides analogue (‘lactide’ is not used in IUPAC names themselves anyway), but they exist.

In traditional or general names, the Greek letter numbering is used, e.g. ε-caprolactam, or β-lactam four-membered ring part in bicyclic penicillin skeleton.

• Lactide is a cyclic lactone di-ester, derived from lactic acid (en.wikipedia.org/wiki/Lactide). Thus, there is no name for lactam version. However, it could be a series of derivatives of piperazine-2,5-diones. Simplest member is piperazine-2,5-dione, derived from glycine. – Mathew Mahindaratne Nov 23 '18 at 8:46
• @MathewMahindaratne Can you please add an answer? It seems comments eventually get deleted... This is good enough for an answer. – AbhigyanC Nov 23 '18 at 11:21
• @AbhigyanC They need to obsolete/not useful etc. and flagged (or deleted by author). I'd expect comments that add important stuff to answer to last. – Mithoron Nov 24 '18 at 21:45

Cyclic amides are known as lactams. They can be a β-lactam which is a 4-membered ring, a γ-lactam which is a 5-membered ring, a δ-lactam which is a 6- membered ring, an ε-lactam which is 7-membered ring, and so on. An example of a drug containing a β-lactam ring is ezetimibe. Antibiotics that contain a β-lactam ring are collectively known as β-lactam antibiotics which include penicillins such as amoxicillin, cephalosporins such as cephalexin, cephamycins such as cefoxitin, carbacephems such as loracarbef, carbapenems such as doripenem, monobactams such as aztreonam, oxacephems such as moxalactam. Examples of drugs containing a γ-lactam ring include levetiracetam, doxapram, glimepiride. Examples of drugs containing a δ-lactam ring include perampanel, milrinone, pirfenidone. Example of a drug containing an ε-lactam ring fused to a benzene ring is benazepril. There are also groups that are half ester and half amide. They are known as carbamates (or urethanes). Some examples of cyclic carbamates are rivaroxaban, metaxalone, zolmitriptan, furazolidone, linezolid etc.