We describe the synthesis of trihydroxylated cyclohexane β-amino acids from (–)-shikimic acid, in their cis and trans configuration, and the incorporation of the trans isomer into a trans-2-aminocyclohexanecarboxylic acid peptide chain. Subsequently, the hydroxyl groups were partially or totally deprotected. The structural study of the new peptides by FTIR, CD, solution NMR and DFT calculations revealed that they all fold into a 14-helix secondary structure, similarly to the homooligomer of trans-2-aminocyclohexanecarboxylic acid. This means that the high degree of substitution of the cyclohexane ring of the new residue is compatible with the adoption of a stable helical secondary structure and opens opportunities for the design of more elaborate peptidic foldamers with oriented polar substituents at selected positions of the cycloalkane residues.
We describe short non-natural peptides that adopt α- and β-turn folds in solution and in the crystal. The peptides are constituted by a core of trans and cis stereoisomers of polyhydroxylated cyclohexane γ-amino acids, flanked by dimers of L-α-alanine, resulting in hybrid hexapeptides with an ααγγαα backbone. DFT calculations and spectroscopic analysis by NMR, CD and FT-IR in solution are consistent with structural changes upon deprotection of certain hydroxyl groups of the central polyhydroxylated γ-amino acids. X-ray diffraction analysis of a crystalline sample revealed a double α-/β-turn that was also identified by NMR spectroscopy in acetonitrile-d3 solution.
We describe the excellent gelation capabilities of amides derived from trans-cyclohexaneβ-amino acid, demonstrating their great potential to generate lypogels in a wide variety of solvents. Structural factors affecting this behavior, like modifying the balance between their hydrophilic/hydrophobic moieties (by changing their alkyl chain length) or their enantiomeric composition (enantiomerically pure compounds vs. racemic mixtures) were investigated. A comprehensive structural analysis ranging from microscopic arrangements to their macroscopic structures is also discussed
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