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Relevant academic research and scientific papers

12/10-Helix in Mixed β-Peptides Alternating Bicyclic and Acyclic β-Amino Acids: Probing the Relationship between Bicyclic Side Chain and Helix Stability

12/10-Helices constitute suitable templates that can be used to design original structures. Nevertheless, they often suffer from a weak stability in polar solvents because they exhibit a mixed hydrogen-bond network resulting in a small macrodipole. In this work, stable and functionalizable 12/10-helices were developed by alternating a highly constrained β2, 3, 3-trisubstituted bicyclic amino acid (S)-1-aminobicyclo[2.2.2]octane-2-carboxylic acid ((S)-ABOC) and an acyclic substituted β-homologated proteinogenic amino acid (l-β3-hAA). Based on NMR spectroscopic analysis, it was shown that such mixed β-peptides display well-defined right-handed 12/10-helices in polar, apolar, and chaotropic solvents; that are, CD3OH, CDCl3, and [D6]DMSO, respectively. The stability of the hydrogen bonds forming the C10 and C12 pseudocycles as well as the benefit provided by the use of the constrained bicyclic ABOC versus typical acyclic β-amino acids sequences when designing 12/10-helix were investigated using NH/ND NMR exchange experiments and DFT calculations in various solvents. These studies showed that the β3-hAA/(S)-ABOC helix displayed a more stable hydrogen-bond network through specific stabilization of the C10 pseudocycles involving the bridgehead NH of the ABOC bicyclic scaffold.

Robust helix formation in a new family of oligoureas based on a constrained bicyclic building block

BAC for more: A constrained bicyclic building block with urea linkages is an efficient combination for the formation of a highly rigid helical system. This type of bicyclic amino carbamoyl (BAC) foldamer was studied both in solution (see scheme) and in the solid state. A robust H-bond (dotted line) network was found between the carbonyl oxygen atoms (red) and the amino groups (dark blue) within the helix. Copyright

Mixed oligoureas based on constrained bicyclic and acyclic β-amino acids derivatives: On the significance of the subunit configuration for folding

The combination of a non-functionalized constrained bicyclo[2.2.2]octane motif along with urea linkages allowed the formation of a highly rigid 2.5 12/14 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 Cαi￡ 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. BAC into the fold: In mixed oligourea alternating (R)-bicyclic amino carbamoyl (BAC)γ and acyclic (S)-β3-homo-amino acid residues, the BAC residue was able to impose a sterically unfavorable Cαi￡C β synclinal conformation to the adjacent acyclic residues, promoting the helical folding of the oligourea (see figure).