Foldamers Based on Oxazolidin-2-ones

Foldamers are artificial molecules capable of organization into well defined secondary structures such as helixes, β-sheets and turns. The essential requirement for an oligomers to qualify for inclusion in the foldamer family is to possess a well defined, repetitive secondary structure, imparted by conformational restrictions imposed by the monomeric unit. These compounds may be composed of subunits of any kind, but most of them contain unusual amino acids and/or aromatic units. We describe the synthesis, the conformation 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, which may be another 4-carboxy oxazolidin-2-one or an amino acid. Such an imido-type function is characterized by a nitrogen atom connected both to an endocyclic and to an exocyclic carbonyl group, and tends always to adopt the trans conformation. As a consequence of this remarkable property, which causes local constraint, these imido-type oligomers are forced to fold in ordered conformations. In combination with interactions of other kinds (H bond, apolar interactions, etc.), these lead to the formation of supramolecular materials. The synthetic approach is highly tuneable with endless variations, so materials with required properties may be prepared “on demand”, simply by changing the design and the synthesis.