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Peptoids are unnatural peptide-like oligomers having the side-chain attached to the glycine nitrogen. In order to investigate how such oligomers are affected upon glycoconjugation, a series of glycosylated peptoids has been synthesized. The conjugation between glycosyl residue and peptoid was achieved by azide + alkyne [3+2] cycloaddition (click reaction). The glycosylated peptoids were obtained by either stepwise assembly from sarcosine and glycosylated monomers or global on-resin click glycoconjugation. CD spectroscopic studies were performed on both unglycosylated and glycosylated peptoids with varying chain-length, revealing length and substituent dependences. Additionally, three peptoids were tested for antifreeze activity.

The Ostwald ripening of polycrystalline ice in aqueous sucrose solutions was investigated experimentally. The kinetics of this ice recrystallization process was studied at temperatures between -6 and -10 degrees C and varying ice volume fractions. Using the theory of Lifshitz, Slyozov, and Wagner (LSW), the diffusion-limited rate constant for ice recrystallization was determined. Also, the effects of synthetic analogues of natural antifreeze glycoproteins (AFGP) were studied. These analogues synAFGPmi (i = 3-5) contained monosaccharide side groups instead of disaccharide side groups that occur in natural AFGP. In order to account for the inhibition effect of the synAFGPmi, we have modified classical LSW theory, allowing for the derivation of inhibition rate constants. It was found that the investigated synAFGPmi inhibit ice recrystallization at concentrations down to approximately 3 microg mL(-1) or, equivalently, approximately 1 micromol L(-1) for the largest synAFGPmi investigated: synAFGPm5. Hence, our new method is capable of quantitatively assessing the efficiency of very similar AFGP with a sensitivity that is at least 2 orders of magnitude larger than that typical for quantitative thermal hysteresis measurements.

Antifreeze glycoproteins enable life at temperatures below the freezing point of physiological solutions. They usually consist of the repetitive tripeptide unit (-Ala-Ala-Thr-) with the disaccharide alpha-D-galactosyl-(1-3)-beta-N-acetyl-D-galactosamine attached to each hydroxyl group of threonine. Monoglycosylated analogues have been synthesized from the corresponding monoglycosylated threonine building block by microwave-assisted solid phase peptide synthesis. This method allows the preparation of analogues containing sequence variations which are not accessible by other synthetic methods. As antifreeze glycoproteins consist of numerous isoforms they are difficult to obtain in pure form from natural sources. The synthetic peptides have been structurally analyzed by CD and NMR spectroscopy in proton exchange experiments revealing a structure as flexible as reported for the native peptides. Microphysical recrystallization tests show an ice structuring influence and ice growth inhibition depending on the concentration, chain length and sequence of the peptides.

Breaking up is easy. Integrin a5b1 is a cell-surface receptor involved in many physiological and pathological processes. Small cyclic peptides can influence the interaction between this receptor and its natural ligand, fibronectin. The peptide shown, c-(-Arg-Gly-Asp-d-Phe- Val-b-Ala-), can bind a5b1 with submicromolar affinity. A conformational analysis of the peptide provided information on the structural properties responsible for binding to a5b1.