CYCLO(L-ALANYL-L-SERYL).H2O AND CYCLO(GLYCYL-L-SERYL)

We have determined the crystal structures of two diletopiperazines, cy clo(L-alanyl-L-seryl).H2O (cis-6-hydroxymethyl-3-methyl-2,5-piperazine dione hydrate, C6H10N2O3.H2O) and cyclo(glycyl-L-seryl) (3-hydroxymeth yl-2,5-piperazinedione, C5H8N2O3). The crystal structure of cyclo(L-al anyl-L-seryl).H2O [cyclo(L-Ala-L-Ser)] consists of a peptide backbone that is hydrogen bonded to two adjacent diketopiperazine rings, formin g extended chains through the crystal. The serine hydroxy group of cyc lo(L-Ala-L-Ser) is hydrated by two adjacent water molecules in the cry stal. In contrast, the crystal structure of cyclo(glycyl-L-seryl) [cyc lo(Gly-L-Ser)] is held together by a three-dimensional network of hydr ogen bonds. The serine hydroxy group of cyclo(Gly-L-Ser) participates in two hydrogen bonds with the peptide backbone of neighboring molecul es.