Detalle de: Non‐natural Amino Acids as Modulating Agents of the Conformational Space of Model Glycopeptides

The synthesis and conformational analysis in aqueous solution of different α‐methyl‐α‐amino acid diamides, derived from serine, threonine, β‐hydroxycyclobutane‐α‐amino acids, and their corresponding model β‐ O ‐glucopeptides, are reported. The study reveals that the presence of an α‐methyl group forces the model peptides to adopt helix‐like conformations. These folded conformations are especially significant for cyclobutane derivatives. Interestingly, this feature was also observed in the corresponding model glucopeptides, thus indicating that the α‐methyl group and not the β‐ O ‐glucosylation process largely determines the conformational preference of the backbone in these structures. On the other hand, atypical conformations of the glycosidic linkage were experimentally determined. Therefore, when a methyl group was located at the Cβ atom with an R configuration, the glycosidic linkage was rather rigid. Nevertheless, when the S configuration was displayed, a significant degree of flexibility was observed for the glycosidic linkage, thus showing both alternate and eclipsed conformations of the ψ s dihedral angle. In addition, some derivatives exhibited an unusual value for the ϕ s angle, which was far from a value of −60° expected for a conventional β‐ O ‐glycosidic linkage. In this sense, the different conformations exhibited by these molecules could be a useful tool in obtaining systems with conformational preferences “à la carte”.