Synthesis and characterization of natural and modified antifreeze glycopeptides: glycosylated foldamers

Abstract

In Arctic and Antarctic marine regions, where the temperature declines below the colligative freezing point of physiological fluids, efficient biological antifreeze agents are crucial for the survival of polar fish. One group of such agents is classified as antifreeze glycoproteins (AFGP) that usually consist of a varying number (n = 4-55) of [AAT]( n )-repeating units. The threonine side chain of each unit is glycosidically linked to β-D: -galactosyl-(1 → 3)-α-N-acetyl-D: -galactosamine. These biopolymers can be considered as biological antifreeze foldamers. A preparative route for stepwise synthesis of AFGP allows for efficient synthesis. The diglycosylated threonine building block was introduced into the peptide using microwave-enhanced solid phase synthesis. By this versatile solid phase approach, glycosylated peptides of varying sequences and lengths could be obtained. Conformational studies of the synthetic AFGP analogs were performed by circular dichroism experiments (CD). Furthermore, the foldamers were analysed microphysically according to their inhibiting effect on ice recrystallization and influence on the crystal habit.

Antifreeze glycopeptide diastereomers

“…The glycosylation of threonine in D- and allo -L-configuration with N- acetyl galactosamine relies on an efficient synthetic procedure by Paulsen et al [21] adapted by us [16,22–23] (Scheme 1). Azidochlorination of a suitably protected L-galactal provides the peracetylated 2-azido-2-desoxygalactopyranosyl chloride serving as a glycosyl donor in a silver-mediated Koenigs–Knorr glycosylation of the particular Fmoc- and t -Bu-protected amino acids, i.e., the allo -L-configured ( 1A ) and D-configured ( 1B ) threonine derivatives.…”

“…Peptide synthesis was accomplished under microwave heating in a semi-automated fashion, as previously published by us [16,23], by employing 2-chlorotrityl resin loaded with Fmoc-L-Ala-OH or Fmoc-D-Ala-OH. After assembly of the glycopeptides the acetate protecting groups of the carbohydrates were cleaved with 5% hydrazine in DMF followed by the cleavage of the peptide from the resin with 2% aqueous TFA.…”

Antifreeze Peptides and Glycopeptides, and Their Derivatives: Potential Uses in Biotechnology

“…These monosaccharide-based AFGP analogues with 3–4 repeating units and sequential variations of the primary structure using glycine, proline, and serine instead of alanine exhibit decreased antifreeze activity compare to the native AFGP sequence. These studies also suggest that the terminal galactose in native AFGP is not necessary for significant activity and underscore the importance of having periodic turns in the peptide sequence [74,75,78,79,80,81]. …”

Analysis of carbohydrates and glycoconjugates by matrix‐assisted laser desorption/ionization mass spectrometry: An update for 2011–2012

“…Threonine glycosidically linked to -DGal-(1 3)--N-acetyl-D-GalN (Nagel et al, 2011) Antifreeze glycopeptides TOF (DHB) Influence of carbohydrate variations on antifreeze activity (Nagel et al, 2012) Antifreeze glycopeptides and glycoproteins TOF (DHB) From dodecapeptide with four GalGalNAc residues (Wilkinson et al, 2012b) Antifreeze glycopeptides and glycoproteins…”