Synthesis of Trifluorinated Threonine and its Incorporation into AFP and AFGP Mimetics.

摘要

The discovery of antifreeze proteins (AFPs) and antifreeze glycoproteins (AFGPs) has sparked the interest of researchers due to its potential commercial, industrial and medicinal applications. AF(G)Ps are unique as they have the ability to suppress the growth of ice. Two physical properties associated with these antifreeze compounds are thermal hysteresis (TH) and ice crystallization inhibition (IRI). It was previously believed that TH and IRI worked hand-in-hand, however, the discovery of an AFP from rye grass possessing only IRI suggested otherwise. It was thus believed that the presence of AFPs possessing only IRI played a vital role in cryoprotection as they allow organisms to survive in the presence of small ice crystals. As such, the synthesis of novel AF(G)Ps possessing only IRI are sought after. Herein, we describe the synthesis of a fluorinated threonine, T(F), and its incorporation in peptides for the synthesis of AFP mimetics ([T(F)AA]4 and [T(F)GG] 4). As the putative binding site of AFP type I is debated, as well as its mode of action, the introduction of a fluorinated threonine may provide insight as it may be used as a tool to investigate the factors influencing antifreeze activity. Furthermore, fluorine amino acids have proven to be beneficial in the production of biologically active agents, thus highlighting the importance of the use of fluorines. The synthetic route to [T(F)AA]4 and [T(F)GG] 4 is described within this thesis, and the results obtained from the TH and IRI assays performed.;*Please refer to dissertation for diagrams.;The synthetic route to the building block T(F) was performed over 13 steps in 15 % yield. The incorporation of T(F) in peptides to build AFP mimetics was done via SPPS. MALDI-TOF spectroscopy revealed a mass peak for the polyalanine AFP analog but was not apparent for [T(F)GG] 4. Nuclear magnetic resonance experiments (19F) revealed a single fluorine resonance for both [T(F)AA]4 and [T(F)GG] 4 suggesting the presence of a fluorinated compound. The repeating nature of these polymers may account for the single resonance observed. The TH assay did not reveal dynamic ice shaping (DIS) or a thermal hysteric gap. The IRI results were unfortunately contradictory but did reveal that the introduction of fluorine into AFPs do not alter the recrystallization inhibition activity as in the case of [T(F)AA]4 and [TAA]4. The outcome of these results may be due to the solubility issues encountered, which affected the concentration and purity of the sample solutions tested. Despite the solubility issues and misrepresentative results, additional experiments ought to be performed to determine the effects of fluorine on antifreeze activity.*