Foldamers Based on Oxazolidin-2-ones

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 will describe the synthesis, the conformational analysis and the physical properties in the solid state of pseudopeptide foldamers containing imido-type functions, obtained by coupling the nitrogen of a 4-carboxy oxazolidin-2-one unit with the carboxylic acid moiety of the next unit, that may be another 4-carboxy oxazolidin-2-one or an amino acid. The imido-type functions are characterized by a nitrogen atom connected both to an endocyclic and to an exocyclic carbonyl which tend to adopt always the trans conformation. As a consequence of this remarkable property that causes a local constrain, these imido-type oligomers are forced to fold in ordered conformations, that, in combination with other kind of interactions (H bond, apolar interactions etc. etc.), lead to the formation of supramolecular materials. The synthetic approach is highly tunable with endless variations, so, simply by changing the design and the synthesis, materials with the required properties may be prepared “on demand”.