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

Abstract

Upon slow evaporation of a 1:1 diastereoisomeric mixture of Boc-(L-Phe-L-Oxd)2-OBn (1; Boc=tert-butyloxycarbonyl; L-Oxd=trans-(4S,5R)-4-carboxy 5-methyloxazolidin-2-one, Bn=benzyloxycarbonyl) and Boc-L-Phe-L-Oxd-D-Phe-L-Oxd-OBn (2) in methyl tert-butyl ether, single crystals suitable for an X-ray diffraction study were obtained. In contrast, the two pure oligomers lead to the formation of amorphous solids under any crystallization conditions. The preferential conformation of both oligomers was fully elucidated in the solid phase and compared with the known conformation of Boc-(L-Phe-D-Oxd)2-OBn (3). The preferred conformation of 1 ranges from a polyproline II (PPII) helix to β strands and we can gather that longer and more structured oligomers will form PPII helices. In contrast, compound 3 forms infinite antiparallel β-sheet structures; thus showing the strong effect of the reversal of the absolute configuration of the Oxd moieties on the secondary structure of these hybrid foldamers. The same outcome was retained in solution, as demonstrated by vibrational circular dichroism analysis. Finally, we have demonstrated that a 1:1 mixture of 1 and 2 leads to the formation of new materials with interesting properties that are missing from the two pure compounds, such as the tendency to form crystals, fibers, and globules, depending on the solvent

Structure of Condensed Phase Peptides: Insights from Vibrational Circular Dichroism and Raman Optical Activity Techniques

“…Alternate sequences including tetra peptides were structurally analyzed in a similar manner, and some other studies on similar sized peptides made use of the noninterference of aromatic residues in VCD. ,,− Additionally, studies of extremely weak amide III VCD for blocked amino acids have also appeared and have been related to PPII forms . Such small oligomer studies, incorporating numerous possible variations of residues and techniques, including nonproteinic residues, have continued with efforts to relate to structural propensity in larger peptides and disordered proteins. ,,− While small oligomer properties have theoretical interest, their impact on the understanding of the structure and spectra for larger peptides and proteins with unique conformation is limited since the larger peptide properties are heavily influenced by the extended sequence and coupling of residues.…”

Pseudopeptide‐Based Hydrogels Trapping Methylene Blue and Eosin Y

“…This molecule belongs to ag roup of foldamers containing the 4-car-boxy-5-methyl-oxazolidin-2-one unit (Oxd) [18] or the p-glutamic acid unit (pGlu). [19] These molecules cause al ocal constraint in the pseudopeptide chain that favours the formationo fs econdary structures, [20][21][22] fibers [23][24][25] and gels. [26][27][28] Thus we prepared hydrogels based on Fmoc-l-Phe-d-pGlu-OH to test them for the adsorptiono fM ethylene Blue (MB), ac ationic dye, and Eosin Y( EY), an anionic dye, as these molecules may be used as model pollutants.…”

Oxazolidinone‐containing pseudopeptides: Supramolecular materials, fibers, crystals, and gels

“…Interestingly very nice crystals suitable for X‐ray diffraction study were obtained on slow evaporation of a 1:1 diastereoisomeric mixture of Boc‐( l ‐Phe‐ l ‐Oxd) 2 ‐OBn 4 and Boc‐ l ‐Phe‐ l ‐Oxd‐ d ‐Phe‐ l ‐Oxd‐OBn 5 in methyl t ‐butyl ether. The preferential conformation of both oligomers was fully elucidated in the solid phase and the X‐ray crystal structures of the two epimers are shown in Figure …”