Synthesis of crescent shaped heterocyclic urea-linked foldamers

Foldamers are oligomers or polymers that have well-defined conformations in solution. The synthesis of tunable, heterocyclic, urea-linked foldamers is described. The curvatures of the foldamers can be altered by varying the heterocylic diazine (pyrazine, pyrimidine, pyridazine) or the non-heterocyclic (tolyl, o -xylyl, m -xylyl) aromatic units. Foldamers comprised of three to five aromatic groups were synthesized. Folding of these oligomers is driven by the restricted rotation along the urea bonds linking the aromatic units. This restricted rotation is caused by the additive effects of non-covalent interactions, particularly intramolecular hydrogen bonding between the urea hydrogen and the heterocyclic nitrogen atoms and steric interaction between the urea carbonyl and the toluene or xylene methyl groups. These foldamers were characterized using NMR, MALDI-TOF-MS, and FTIR. To the best of our knowledge, these are the first urea-based foldamers where curvature of the macromolecule can be easily controlled by varying either the heterocyclic or non-heterocyclic aromatic segments