Oxazolidin-2-one-Containing Pseudopeptides That Fold into β-Bend Ribbon Spirals

Abstract

Three sets of oligomers containing the 4-carboxy-5-methyloxazolidin-2-one (Oxd) moiety have been synthesized with the aim of checking whether these molecules are able to fold in ordered structures: A set [Boc-(L-Ala-L-Oxd)(n)-OR], B set [Boc-(L-Ala-D-Oxd)(n)-OR], and C set [Boc-(Aib-L-Oxd)(n)-OR] preferential conformations have been analyzed with IR absorption, NMR, and CD. We have noticed that in these oligomers three stabilizing effects are active: (i) the rigid Oxd -CO-N(CH<)-CO- moiety, which always tend to assume a trans conformation; (ii) the formation of Oxd C=O...H-(alpha)C intramolecolar H-bonds; (iii) the alternate formation of 1 <-- 4 intramolecular C=O...H-N H-bonds. Through the analysis of the experimental data, we could demonstrate that only the oligomers of the B set are able to meet all three requirements listed above. By a deeper insight into the CD spectra, we gathered that the secondary structure adopted by the B set oligomers is a beta-bend ribbon spiral, which is a subtype of the 3(10)-helix.

Solid‐State Properties and Vibrational Circular Dichroism Spectroscopy in Solution of Hybrid Foldamers Stereoisomeric Mixtures

“…assignment of longer oligomers, which were dissolved in methanol, was more complicated because, in these cases, mixtures of conformers were present in solution; nevertheless, a PPII conformation could be taken into account. This outcome is very different from the results obtained with other oligomers, in which the d-Oxd moiety is alternated with l-amino acids: Boc-(l-Ala-d-Oxd) n -OBn [5] and Boc-…”

Chiral Gold Nanoparticles Decorated with Pseudopeptides

“…[13] A similar trend was observed for the C=O stretching band of the amide groups, which shift from 1679 cm -1 in 1 to 1663 cm -1 in 4. By contrast, two bands at 3436 and 3347 cm -1 are seen in the spectrum of 2, indicating that both free and hydrogenbonded amide NH groups are present in solution.…”

“…Before linking compounds 1-4 to AuNPs, the possible adoption of a well-defined secondary structure in these compounds, as in the previously studied N-Boc derivatives, [13] was investigated by IR and NMR spectroscopy and by single-crystal X-ray diffraction. The N-H stretching region enables intramolecular C=O···H-N hydrogen bonds formed in solution to be detected; free (non-hydrogenbonded) amide NH groups exhibit a stretching signal above 3400 cm -1 , whereas hydrogen-bonded amides [14] produce a stretching band below 3400 cm -1 .…”

Synthesis and Secondary Structure of Alternate α,β‐Hybrid Peptides Containing Oxazolidin‐2‐one Moieties

“…These preliminary results suggest that the longer oligomers of this series form strong hydrogen bonds, as was observed for the oligomers of the -Ala--Oxd series. [9] Figure 2. FT-IR absorption spectra in the NH stretching region for 3 m samples of oligomers 2, 5, 7, 9, 11, and 13 in pure CH 2 Cl 2 at room temperature.…”