Synthesis of an Isotopically-labelled Antarctic Fish Antifreeze Glycoprotein Probe

Abstract

Antifreeze glycoproteins (AFGPs) are glycosylated polypeptides produced by Antarctic and Arctic fishes, which allow them to survive in seawater at sub-zero temperatures. An investigation into the postulated enteric uptake of AFGP synthesized in the exocrine pancreas of Antarctic fishes required a custom-prepared AFGP probe that incorporated seven isotopically-labelled Ala residues for detection by mass spectrometry. The AFGPs are composed of a repetitive three amino acid unit (Ala-Ala-Thr), in which the threonine residue is glycosylated with the disaccharide β-d-Gal-(1→3)-α-d-GalNAc. The synthesis of isotopically-labelled AFGP8 (1), as well as the optimized synthesis of the protected glycosylated amino acid building block 2, is reported.