.alpha.,.gamma.-Diacipiperazine 106-57-0 2,5-Diketopiperazine 2,5-Dioxopiperazine 2,5-Piperazinedione Cyclic(glycylglycyl) Cyclo(glycylglycyl) Cyclodiglycine Cycloglycylglycine Diglycolyl diamide Diketopiperazine Glycine, N-glycyl-, cyclic peptide Glycine, bimol. cyclic peptide Glycylglycine lactam NSC26345