# 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