Yes / The disulfide bond plays an important role in the formation and stabilisation of higher order structures of peptides and proteins, while in recent years interest in this functional group has been extended to carbohydrate chemistry. Rarely found in nature, glycosyl disulfides have attracted significant attention as glycomimetics, with wide biological applications including lectin binding, as key components of dynamic libraries to study carbohydrate structures, the study of metabolic and enzymatic studies, and even as potential drug molecules. This interest has been accompanied and fuelled by the continuous development of new methods to construct the disulfide bond at the anomeric centre. Glycosyl disulfides have also been exploited as versatile intermediates in carbohydrate synthesis, particularly as glycosyl donors. This review focuses on the importance of the disulfide bond in glycobiology and in chemistry, evaluating the different methods available to synthesise glycosyl disulfides. Furthermore, we review the role of glycosyl disulfides as intermediates and/or glycosyl donors for the synthesis of neoglycoproteins and oligosaccharides, before finally considering examples of how this important class of carbohydrates have made an impact in biological and therapeutic contexts. / The authors thank the Institute of Cancer Therapeutics (University of Bradford) Doctoral Training Centre for financial support.

The Lattrell-Dax method of nitrite-mediated substitution of carbohydrate triflates is an efficient method to generate structures of inverse configuration. In this study, the effects of the neighboring group on the Lattrell-Dax inversion were explored. A new carbohydrate/anion host-guest system was discovered and the ambident reactivity of the nitrite anion was found to cause a complicated behavior of the reaction. It has been demonstrated that a neighboring equatorial ester group plays a highly important role in this carbohydrate epimerization reaction, restricting the nitrite N-attack, thus resulting in O-attack only and inducing the formation of inversion compounds in good yields. Based on this effect, efficient synthetic routes to a range of carbohydrate structures, notably β-D-mannosides and β-D-talosides, were designed by use of double parallel and double serial inversion. A supramolecularly activated, triggered cascade reaction was also developed. This cascade reaction is triggered by a deprotonation process that is activated by anions. It was found that the anions can activate this reaction following their hydrogen bonding tendencies to the hydroxyl group in aprotic solvents. / QC 20100709

Inhibiting the formation of ice is an essential process commercially, industrially, and medically. Compounds that work to stop the formation of ice have historically possessed drawbacks such as toxicity or prohibitively high active concentrations. One class of molecules, ice recrystallization inhibitors, work to reduce the damage caused by the combination of small ice crystals into larger ones. Recent advances made by the Ben lab have identified small molecule carbohydrate analogues that are highly active in the field of ice recrystallization and have potential in the cryopreservation of living tissue. A similar class of molecules, kinetic hydrate inhibitors, work to prevent the formation of another type of ice – gas hydrate. Gas hydrates are formed by the encapsulation of a molecule of a hydrocarbon inside a growing ice crystal. These compounds become problematic in high pressure and low temperature areas where methane is present - such as an oil pipeline. A recent study has highlighted the effects of antifreeze glycoprotein, a biological ice recrystallization inhibitor, in the inhibition of methane clathrates. Connecting these two fields through the synthesis and testing of small molecule ice recrystallization inhibitors in the inhibition of methane hydrates is unprecedented and may lead to a novel class of compounds.

The synthesis of glycoconjugates is of interest in biological and medicinal research. There are numerous approaches to the synthesis of glycosides involving protecting group free methods. This thesis outlines what has been achieved in the field and two novel approaches for O-glycosidation. The first approach involves the use of a toluenesulfonohydrazide glycoside with a purification handle designed for simple glycoside purifications. The butyl 3-O-octyl-D-glucopryanoside was successfully synthesized but did not have the desired property of yielding simple-to-purify glycosides as products. The second approach uses a thiouronium glycosyl donor; a variety of glycosidations using this donor were investigated. The glucosyl thiouronium salt donor was shown to undergo glycosidation effectively with simple alcohols.

The synthesis of glycoconjugates is of interest in biological and medicinal research. There are numerous approaches to the synthesis of glycosides involving protecting group free methods. This thesis outlines what has been achieved in the field and two novel approaches for O-glycosidation. The first approach involves the use of a toluenesulfonohydrazide glycoside with a purification handle designed for simple glycoside purifications. The butyl 3-O-octyl-D-glucopryanoside was successfully synthesized but did not have the desired property of yielding simple-to-purify glycosides as products. The second approach uses a thiouronium glycosyl donor; a variety of glycosidations using this donor were investigated. The glucosyl thiouronium salt donor was shown to undergo glycosidation effectively with simple alcohols.

Inhibiting the formation of ice is an essential process commercially, industrially, and medically. Compounds that work to stop the formation of ice have historically possessed drawbacks such as toxicity or prohibitively high active concentrations. One class of molecules, ice recrystallization inhibitors, work to reduce the damage caused by the combination of small ice crystals into larger ones. Recent advances made by the Ben lab have identified small molecule carbohydrate analogues that are highly active in the field of ice recrystallization and have potential in the cryopreservation of living tissue. A similar class of molecules, kinetic hydrate inhibitors, work to prevent the formation of another type of ice – gas hydrate. Gas hydrates are formed by the encapsulation of a molecule of a hydrocarbon inside a growing ice crystal. These compounds become problematic in high pressure and low temperature areas where methane is present - such as an oil pipeline. A recent study has highlighted the effects of antifreeze glycoprotein, a biological ice recrystallization inhibitor, in the inhibition of methane clathrates. Connecting these two fields through the synthesis and testing of small molecule ice recrystallization inhibitors in the inhibition of methane hydrates is unprecedented and may lead to a novel class of compounds.

Inhibiting the formation of ice is an essential process commercially, industrially, and medically. Compounds that work to stop the formation of ice have historically possessed drawbacks such as toxicity or prohibitively high active concentrations. One class of molecules, ice recrystallization inhibitors, work to reduce the damage caused by the combination of small ice crystals into larger ones. Recent advances made by the Ben lab have identified small molecule carbohydrate analogues that are highly active in the field of ice recrystallization and have potential in the cryopreservation of living tissue. A similar class of molecules, kinetic hydrate inhibitors, work to prevent the formation of another type of ice – gas hydrate. Gas hydrates are formed by the encapsulation of a molecule of a hydrocarbon inside a growing ice crystal. These compounds become problematic in high pressure and low temperature areas where methane is present - such as an oil pipeline. A recent study has highlighted the effects of antifreeze glycoprotein, a biological ice recrystallization inhibitor, in the inhibition of methane clathrates. Connecting these two fields through the synthesis and testing of small molecule ice recrystallization inhibitors in the inhibition of methane hydrates is unprecedented and may lead to a novel class of compounds.

Cryopreservation is a method used to preserve the quality of various cell types over long periods of time (up to several years). Using this preservation method can vastly improve cellular therapies and regenerative medicine by allowing the creation of biobanks containing high-quality cell products. For example, biobanks of red blood cells (RBCs) would be beneficial for cellular therapies such as RBC transfusions, which are used to treat patients suffering from hemorrhages, anemias, and to replace blood loss after traumatic/surgical events. RBCs are currently preserved via hypothermic storage which limits their shelf life to 42 days. Similarly, biobanks of hematopoietic stem cells (HSCs) from umbilical cord blood would be beneficial for regenerative medicine therapies such as HSC transplantations, which offer treatment for blood- and immune-related diseases by reconstituting hematopoiesis. The outcome of these transplantations depends greatly on the quality of the cell product; therefore, it is important for preserved HSCs to have a minimum loss of viability and functionality. The cryopreservation of cells at low sub-zero temperatures (-80 to -196 degC) in a cryoprotectant solution allows for long-term storage. Common cryoprotectants used are 40% glycerol for the cryopreservation of RBCs and 10% dimethyl sulfoxide (DMSO) for the cryopreservation of HSCs. Before clinical use of cryopreserved products, DMSO and glycerol must be removed as they are severely toxic to patients upon infusion. The removal of 40% glycerol from RBCs is complicated, time consuming, and can result in a significant amount of cell damage. DMSO and glycerol also do not address the occurrence of ice recrystallization, which is the main cause of cellular damage during cryopreservation. Ice recrystallization describes the process of ice crystals growing larger and replacing smaller ice crystals, and significantly contributes to the damage of cells post-thaw. Therefore, methods to decrease the concentration of cryoprotectants to improve their removal process while also mitigating ice recrystallization is of interest. In nature, antifreeze proteins and glycoproteins (AF(G)Ps) are found in animals that can survive below-freezing temperatures. The Ben laboratory has used the structural components of AF(G)Ps to design several small-molecule carbohydrates that exhibit ice recrystallization (IRI) activity. O-aryl-b-D-glucosides and N-aryl-D-gluconamides are two classes of IRIs developed that have been used as supplemental additives to DMSO and glycerol to improve the post-thaw viabilities and functionalities of RBCs and HSCs. While many structure-activity relationship studies have been performed amongst these classes, one area of improvement is their solubilities to facilitate their use as cryoprotectants. This thesis focuses on the design of a new class of effective IRIs that have high solubilities (>100 mM in phosphate-buffered saline). Previous studies on the structure of small-molecule IRIs have demonstrated the importance of balancing the hydrophobicity and hydrophilicity within a molecule, making it difficult to achieve high solubilities. This thesis further explores this point by the design and synthesis of IRIs with polar functional groups possessing an overall molecular charge. N-aryl-D-gluconamides bearing amino- and azido-substituents were designed, however their synthesis was unsuccessful. Instead, this work revealed a synthetically facile route towards N-xylo-L-furanosyl amide and ester compounds. Phosphonate-substituted carbohydrates were also designed and synthesized as a means to obtain highly soluble IRIs. All of these compounds displayed high solubilities, however the majority of the compounds exhibited moderate IRI activities. While there are many assays used to measure IRI activity, this thesis also evaluates two of the most common IRI assays and their effect on IRI activity. In addition, the effect that cryoprotective agents (CPAs) like DMSO and glycerol have on IRI activity was also evaluated. In both cases, the type of assay used and the addition of CPAs affected the quantitative values describing IRI activity. Notably, DMSO and glycerol, had an antagonistic effect on the IRI activity of N-aryl-D-gluconamides and antifreeze protein type I. This was a significant observation since these IRIs are sufficient cryoprotectants in the presence of DMSO or glycerol. Lastly in this thesis, phosphonate-substituted IRIs and antifreeze (glyco)proteins (AF(G)Ps) were evaluated as cryoprotectants for the cryopreservation of RBCs and/or HSCs. These studies showed that phosphonate IRIs and AF(G)Ps were not toxic to RBCs and/or HSCs, however the concentrations evaluated were unable to improve the post-thaw viability and/or functionality of these cell types.

<p>The Lattrell-Dax method of nitrite-mediated substitution of carbohydrate triflates is an efficient method to generate structures of inverse configuration. In this study it has been demonstrated that a neighboring equatorial ester group plays a highly important role in this carbohydrate epimerization reaction, inducing the formation of inversion compounds in good yields. Based on this effect, efficient synthetic routes to a range of carbohydrate structures, notably β-D-mannosides and β-D-talosides, were designed. By use of the ester activation effect for neighboring groups, a double parallel as well as a double serial inversion strategy was developed.</p>

The cryopreservation of cells and tissues requires the addition of a cryoprotectant in order to prevent cellular damage caused by ice. Unfortunately, common cryoprotectants such as DMSO and glycerol exhibit significant toxicity which makes their use unfeasible for many clinical procedures. Our laboratory is interested in the development of alternative, non-toxic cryoprotectants which possess ice recrystallization inhibition (IRI) activity. Potent IRI activity has recently been discovered in certain small molecules, but the structural features required for this process are unclear. Herein we report the development of a library of O-aryl glycosides in order to probe the importance of electron density and hydrophobic moieties for IRI activity. It was found that the degree of electron density at the anomeric oxygen does not correlate with IRI ability in para-substituted aryl glycosides, nor does changing the position of the aryl substituent impart a predictable effect on activity. However, the addition of hydrophobic alkyl or acyl chains was beneficial for IRI activity; generally, increasing chain length was found to correlate with increasing activity. In some instances, an optimal alkyl chain length was identified, after which continued lengthening results in a loss of potency. We conclude from this study that a certain extent of hydrophobic character is beneficial for the IRI activity of aryl glycosides, and that a balance between hydrophobicity and hydrophilicity is required for optimum IRI ability. It is hoped that these findings will aid future efforts towards the rational design of novel cryoprotectants.