Oxazolidin-2-one Based Foldamers for the Formation of Supramolecular Materials

Foldamers are artificial molecules able to get organized in well defined secondary structures, such as helixes, -sheets and turns. 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. These compounds may be composed of any kind of subunits, but most of them contain unusual amino acids and/or aromatic units. We have recently studied the synthesis, the conformational analysis and the application as supramolecular materials of foldamers containing the 4-carboxy oxazolidin-2-one unit or related molecules, where an imido-type function is obtained by coupling the nitrogen of the heterocycle with the carboxylic acid moiety of the next unit. The imide group is characterized by a nitrogen atom connected to an endocyclic and an exocyclic carbonyl which tend to adopt always the trans conformation. As a consequence of this locally constrained disposition effect, these imide-type oligomers are forced to fold in ordered conformations, such as PPII helixes, -band ribbon spirals, -sheets and - or -turns and a wide variety of unusual secondary structures are obtained from hybrid foldamers. In the solid state, some of these compounds form supramolecular materials, such as fibers, layers and gels, that may be used for several applications. The synthetic approach is highly tunable with endless variations, so, simply by changing the design and the synthesis of the foldamer, a supramolecular material with the required properties may be prepared “on demand”.