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The design of a new β-turn inducer is correlated to the discovery of new foldamers. In this paper, we report the liquid phase synthesis of 2:1 [α/aza]-oligomers using a convergent Boc strategy. The NMR, FTIR, restrained molecular dynamics and X-ray diffraction analyses show that 2:1 [α/aza]-oligomers adopt a C=O( i) ···H-N( i + 2) hydrogen-bonded helical conformation. [ABSTRACT FROM AUTHOR]

α,β-Hybrid oligomers of varying lengths with alternating proteogenic α-amino acid and the rigid β2,3,3-trisubstituted bicyclic amino acid ABOC residues were studied using both X-ray crystal and NMR solution structures. While only an 11/9 helix was obtained in the solid state regardless of the length of the oligomers, conformational polymorphism as a chain-length-dependent phenomenon was observed in solution. Consistent with DFT calculations, we established that short oligomers adopted an 11/9 helix, whereas an 18/16 helix was favored for longer oligomers in solution. A rapid interconversion between the 11/9 helix and the 18/16 helix occurred for oligomers of intermediate length. [ABSTRACT FROM AUTHOR]

The combination of a non-functionalized constrained bicyclo[2.2.2]octane motif along with urea linkages allowed the formation of a highly rigid 2.512/14 helical system both in solution and the solid state. In this work, we aimed at developing stable and functionalized systems as promising materials for biological applications in investigating the impact of this constrained motif and its configuration on homo and heterochiral mixed-oligourea helix formation. Di-, tetra-, hexa-, and octa-oligoureas alternating the highly constrained bicyclic motif of ( R) or ( S) configuration with acyclic ( S)-β3-amino acid derivatives were constructed. Circular dichroism (CD), NMR experiments, and the X-ray crystal structure of the octamer unequivocally proved that the alternating heterochiral R/ S sequences form a stable left-handed 2.5-helix in contrast to the mixed ( S/ S)-oligoureas, which did not adopt any defined secondary structure. We observed that the (−)-synclinal conformation around the CαCβ bond of the acyclic residues, although sterically less favorable than the (+)-synclinal conformation, was imposed by the ( R)-bicyclic amino carbamoyl (BAC) residue. This highlighted the strong ability of the BAC residue to drive helical folding in heterochiral compounds. The role of the stereochemistry of the BAC unit was assessed and a model was proposed to explain the misfolding of the S/ S sequences. [ABSTRACT FROM AUTHOR]

9‐Helix: 4‐Amino(methyl)‐1,3‐thiazole‐5‐carboxylic acids (ATCs) were synthesized as new γ‐amino acid building blocks. The structures of various ATC oligomers were analyzed in solution by CD and NMR spectroscopy and in the solid state by X‐ray crystallography. The ATC sequences adopted a well‐defined 9‐helix structure in the solid state and in aprotic and protic organic solvents as well as in aqueous solution. [ABSTRACT FROM AUTHOR]

Carbohydrates bearing both amino and carboxylate groups could be useful for expanding the repertoire of monomers used for building foldamers. In this paper, we give a full account of the synthesis of small hybrid γ/α-glycopeptides built with sugar γ-amino acids and l -alanine. The γ/α-glycopeptides obtained are the first featuring geminally β,β-disubstituted γ-amino acids in which the β-carbon is the pseudo anomeric carbon of a sugar ring. Their conformational properties were studied by NMR and solution infrared spectroscopy, circular dichroism and molecular dynamics simulation. [ABSTRACT FROM AUTHOR]