Diketopiperazine

2,5-diazacyclohexane-1,4-dione. C ₄ H ₆ N ₂ O ₂ (114.10). There are three isomers, 2,3-, 2,5-, and 2,6-diketopiperazine, depending on the position of the carbonyl group, but 2,5-diketopiperazine is the most important. 2,5-diketopiperazine is the anhydride of two glycine molecules, and when recrystallized from water it becomes plate-like crystals, and when sublimated it becomes needle-like crystals. Melting point 311-312 °C (decomposition). It sublimes at 260 °C. It is sparingly soluble in cold water, but soluble in hot water. It dissolves in hydrochloric acid and precipitates with alcohols. It is also easily hydrolyzed with alkali. Derivatives in which the hydrogen atoms of the two methylene groups are replaced by alkyl groups or the like are also called diketopiperazines, and are considered to be anhydrides formed by dehydration condensation of the same or different α-amino acids. It is produced by thermal dehydration of α-amino acids or by self-condensation of esters.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

2,5-diazacyclohexane-1,4-dione．C₄H₆N₂O₂(114.10)．カルボニル基の位置により，2,3-，2,5-，2,6-ジケトピペラジンの3種類の異性体があるが，2,5-ジケトピペラジンがもっとも重要である．2,5-ジケトピペラジンは，グリシン2分子の無水物に相当し，水より再結晶すると板状結晶，昇華により針状結晶となる．融点311～312 ℃(分解)．260 ℃ で昇華する．冷水に難溶，熱水に可溶．塩酸に溶け，アルコール類により沈殿する．また，アルカリにより容易に加水分解される．二つのメチレン基の水素原子をアルキル基などで置換した誘導体も，同じくジケトピペラジンとよばれ，同種または異種のα-アミノ酸が脱水縮合した無水物と考えられる．α-アミノ酸の加熱脱水，またはエステルの自己縮合により生じる．

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