The incorporation of flexible aliphatic units into otherwise rigid aromatic foldamer sequences may result in different outcomes. The flexible units may have conformational preferences of their own that can be expressed orthogonally to those of the aromatic units. Alternatively, the latter may dictate their folding behavior onto the former. Hybrid aliphatic–aromatic peptidic oligomers combining oxazole-based (O) and quinoline-based (Q) amino acids have been synthesized, and their folding behavior has been investigated in solution by NMR spectroscopy and CD spectroscopy, and in the solid state by X-ray crystallography. Sequences based on the OQQ repeat motif were shown to fold into a canonical aromatic helix motif dominated by the preferences of the quinoline, whereas sequences based on OQ repetitions preferred to fold into a herringbone helix in which the conformational preference of the oxazole units is also expressed.

Cyclic triamides 4 bearing amidino groups at the meta position of the phenyl rings were synthesized, and their conformational properties in the crystal and in solution were examined. Compound 4a exists as a capsule-type dimer of the enantiomers with a bowl-shaped syn conformation in the crystal state. Compound 4 exists mainly in the syn form in solution, and chiral induction was observed upon addition of a chiral acid to a solution of 4a. Chirality 27:487–491, 2015. © 2015 Wiley Periodicals, Inc.

Aromatic N,N′-dimethylated urea exists in (cis, cis) form, both in the crystal and in solution, and this structure can be utilized to construct intramolecular aromatic multilayered oligomers. These structures show helical conformation with all-R or all-S axis chirality, when the benzene rings are connected at the meta positions. To investigate the dynamic conformational behavior of such aromatic multilayered ureas in various solvents, we synthesized tetra(m-phenylurea) 3 bearing two chiral N-2-(methoxyethoxyethoxy)propyl groups and six N-methoxyethoxyethyl groups. The high solubility of compound 3 enabled its analysis in various solvents, including water. The CD spectra of compound 3 showed broad electronic absorption with high temperature-dependency, owing to the induction of handedness, in acetonitrile, chloroform, and methanol. In water, the CD signals of compound 3 indicated the presence of similar helical structure, but temperature-dependency was not observed. Chirality, 2011. © 2011 Wiley Periodicals, Inc.