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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.

References in periodicals archive ?
Cyclo(L-Tyr-L-Pro) (diketopiperazine) and o-hydroxyemodin (anthraquinone) exhibited potent inhibitory effect on HCV NS3-NS4A protease with mild interfere with human physiological processes requiring trypsin activity, which warrants for further investigation of other members of these widely distributed class of diketopiperazines and anthraquinones in marine and terrestrial metabolites.
The company said that the protected compositions contain either DA-DKP, a cyclic dipeptide diketopiperazine, which is the active ingredient of Ampion, but also extend to many other diketopiperizines.