Oxazolidin-2-ones-Containing Pseudopeptides that Fold into Secondary Structures

Oligomers capable of folding into defined secondary structures (“foldamers”) have recently received considerable attention. Indeed simplified artificial systems based on artificial backbones designed to fold in secondary structures may be used for the de novo design of molecules with interesting biological activities. 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. The synthesis and the conformational analysis of pseudopeptide oligomers, formed of homogeneous or heterogeneous backbones will be shown. Indeed, heterogeneous backbones, composed of two or more residue types, can also display well-defined folding behaviour, which lead to different types of secondary structures.