Also known as dioxopiperazines, piperazine-2,5-diones or DKPs. Diketopiperazines may occur as by-products during peptide synthesis or during the degradation of peptides. These cyclic dipeptides have been detected as taste-modulating compounds in food, they often show biological activity. DKPs are valuable chiral synthons, employed e.g. in Schöllkopf's versatile bislactim ether approach. They also have found use as catalysts for enantioselective synthesis, e.g. in the asymmetric Strecker reaction. See also the TRH metabolite cyclo(-His-Pro), G-1745, and cyclo(-Asp-Phe), G-1695, the major degradation product of aspartame.

Catalyst for asymmetric cyanohydrin synthesis. The addition of hydrogen cyanide to benzaldehyde gives the highest optical yield ever obtained for the corresponding cyanohydrin. In a study of McCleland et al., G-1740 showed significant anti-tumour activity, causing reduction of cell viability in cervical cancer cells. In isolated rat hearts, the diketopiperazine caused a gradual reduction of heart rate and a decrease in coronary flow rate.