Novel sulphur-linked AFGP analogues: Synthesis and evaluation of antifreeze activity

Antifreeze Glycoproteins (AFGPs) are peptide based compounds found in various organisms. They are a subclass of Biological antifreezes which are especially important for fish that live in polar waters; they inhibit the growth of ice and are thus keys to the survival of these organisms. The mechanism by which these compounds inhibit ice growth is regarded as absorption-inhibition at the macromolecular level. However the mechanism of action on the molecular level is widely debated among researchers.;These analogues were evaluated for antifreeze-specific activity; recrystallization inhibition (RI), thermal hysteresis (TH) and dynamic ice shaping (DIS). None of the analogues showed thermal hysteresis activity and one showed weak dynamic ice shaping properties. The results from the IRI assay showed that the substitution of an electronegative atom at the anomeric position greatly reduces IRI activity. This follows a trend that was seen previously where the substitution of oxygen at the anomeric position also results in loss of activity. These results suggest that an anomeric carbon is necessary for optimal IRI activity within these systems and that is quite likely that the anomeric effect plays an important role in the loss of activity seen when an electronegative atom is present. These results are outlined in this thesis and provide us with important information towards a unified understanding of the mechanism of action of these compounds.;The Ben lab has been designing AFGP analogues possessing enhanced chemical stability and biological activity for the purpose of structure activity studies. One of the most stable and potent analogues are the C-linked AFGP analogues. To improve our understanding of the effect of the nature of the atom at the anomeric position, a series of analogues possessing a sulphur atom at that position have been synthesized. The requisite glycosylated building blocks were synthesized via a modified protocol developed by Chi-Huey Wong and coworkers. The resulting building blocks were then assembled into antifreeze glycoprotein analogues using an automated solid phase synthesizer.