The essential requirement for an oligomer to be included in the foldamer family is to possess a well defined, repetitive secondary structure, imparted by conformational restrictions of the monomeric unit. In this connection we described the preparation and the conformational analysis of pseudopeptides containing the 4-carboxy oxazolidin-2-one unit: these compounds contain a cyclic urethane moiety, so that by coupling it with a carboxylic acid derivative an imido-type function is obtained. This latter group is characterized by a nitrogen atom connected to an endocyclic and an exocyclic carbonyl which tend to adopt the trans conformation. As a consequence of this locally constrained disposition effect, these imide-type oligomers are forced to fold in an ordered conformation, that can lead, in the solid state to the formation of fibers or platelets.