A diketopiperazine (DKP), also known as a dioxopiperazine or piperazinedione, is a class of organic compounds related to piperazine but containing two amide linkages. DKP's are the smallest known class of cyclic peptide. Despite their name, they are not ketones, but amides. Three regioisomers are possible, differing in the locations of the carbonyl groups.
* One isomer is an oxamide obtained from ethylenediamine.
* 2,5-Diketopiperazines are cyclodipeptides often obtainable via condensation of two α-amino acids.
* 2,6-Diketopiperazines may be viewed as cyclized imide derivatives derived from iminodiacetic acids.
Of these three isomeric diketopiperazines, the 2,5-derivatives have attracted the greatest interest. Due to their appearance in biologically active natural products, medicinal chemists have been inspired to use DKPs to circumvent the poor physical and metabolic properties of peptides in the course of drug discovery.