A conformational study of the terpolymer of glycine and its retropeptides monomethylendiamine (gGly) and malonyl (mGly) with sequence : (-Gly-gGly-mGly-), is presented. First, we investigated the conformational preferences of the model molecule 2,5,9,11-tetraoxo-3,6,8,12-tetraza-tridecane using quantum mechanical calculations. The results indicated that the compound has a strong tendency to fold, giving intramolecular hydrogen bonds. Interestingly, the C-13 (intramolecular 13-membered ring hydrogen-bonded system) con formation, which is the pattern of an alpha-helix conformation, was characterized as a minimum. Force-field calculations in an infinite chain model showed that there are two preferred conformations to this regular polyretropeptide. These correspond to an alpha-helix and a 6-fold helix stabilized by intramolecular and intermolecular hydrogen bonds, respectively.