six-membered heterocyclic compounds that are piperazine derivatives. They are cyclic anhydrides of ±-amino acids:

Diketopiperazines are colorless crystals. Neutral compounds, they are readily soluble in hot water, but only slightly soluble in cold water. The hydrolysis of diketopiperazines yields dipeptides, then amino acids. Sodium in alcohol reduces diketopiperazines to piperazines.

Diketopiperazines can be made by cyclizing a-amino acids or their esters; they can also be isolated from the hydrolisates of proteins.