Cyclo(L-alanyl-L-seryl).H₂O and Cyclo(glycyl-L-seryl)

We have determined the crystal structures of two diketopiperazines, cyclo(L-alanyl-L-seryl).H₂O, (cis-6-hydroxymethyl-3-methyl-2,5- piperazinedione hydrate, C₆H₁₀N₂O₃.H₂O and cyclo(glycyl-L-seryl), 3-hydroxymethyl-2,5-piperazinedione, C₅H₈N₂O₃. The crystal structure of cyclo(L-alanyl-L-seryl).H₂O [cyclo(L-Ala-L-Ser)] consists of a peptide backbone that is hydrogen bonded to two adjacent diketopiperazine rings, forming extended chains through the crystal. The serine hydroxyl of cyclo(L-Ala-L-Ser) is hydrated by two adjacent water molecules in the crystal. In contrast, the crystal structure of cyclo(Glycyl-L-seryl) [cyclo(Gly L-Ser)] is held together by a three-dimensional network of hydrogen bonds. The serine hydroxyl of cyclo(Gly L-Ser) participates in two hydrogen bonds with the peptide backbone of neighboring molecules.

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