Natural killer T cells (NKT cells) are a subset of T cells. They regulate a wide range of diseases including infection, tumor growth, and autoimmune diseases, through recognizing glycolipid antigens in the context of CD1d. An understanding of the scope of glycolipid antigens would facilitate use of this cell type in controlling immune responses. Till today, a lysosomal glycolipid, isoglobotrihexosylceramide (iGb3), is the only natural glycolipid that has been found to be recognized by both human and mouse NKT cells. To elucidate the molecular basis of this specific recognition, iGb3 variants were designed and prepared: i) replacement of the C26 acyl chain with shortened acyl chains; ii) replacement of the distal galactose with glucose and mannose; iii) replacement of the intermediate galactose with glucose; iv) replacement of the proximal glucose with galactose. Among these glycolipids, the iGb3 variants with shortened acyl chains are potent stimulators of NKT cells. The iGb3 variant with intermediate glucose also showed the ability to stimulate NKT cells, but this finding needs to be verified. Our findings support the specific recognition of iGb3 by NKT cells. The search for other natural glycolipid antigens focuses on glycolipids that are isolated from bacteria and parasites. Recently, glycosphingolipids (GSL-1, -3, and -4) isolated from the sphingomonodaceae family of bacteria were characterized. GSL-1 has been shown to be a potent stimulator of NKT cells. Moreover, it has been reported that GSL-4 is a stimulator as well. To verify the structures and stimulatory properties of GSLs, GSL-1 to -4 were prepared and tested for their abilities to stimulate NKT cells. The result that only GSL-1 can stimulate NKT cells suggests that synthesis of these higher order GSLs would be an immune evasion mechanism. Neutral glycosphingolipids from sheep-derived F. hepatica liver flukes, a causative agent of fascioliasis, were isolated and characterized. Their structures are closely related to iGb3. Among these glycolipids, neo-iGb4s could be truncated to iGb3 in the lysosome and thus stimulate NKT cells. To test this hypothesis, these glycosphingolipids were prepared and tested. None of these synthetic glycolipids stimulates NKT cells, which suggests that the secretion of these glycolipids by F. hepatica could be the result of the parasite-immune-evasion mechanism.

The synthesis of the three 6”-deoxy-6”-thio glycolipid analogues β-D-Gal-(1→6)-β-D-Gal-(1→4)-β-D-Glu-(1→OCH2)-[1,2,3]-triazole-1-dodecane, β-D-Gal-(1→4)-β-D-Glu-(1→4)- β-D-Glu-(1→OCH2)-[1,2,3]-triazole-1-dodecane and β-D-Gal-(1→4)-β-D-Glu-(1→4)-β-D-Glu-(1→OCH2)-[1,2,3]-triazole-1-octadecane is presented here. Glycosylation at position O-4’ of a propargyl cellobioside glycosyl acceptor and position O-6’ of a propargyl lactoside glycosyl acceptor with a 6-thio-6-deoxy galactosyl donor gave rise to two unique trisaccharides that in turn underwent copper-catalyzed azide-alkyne cycloadditions with either 1-azidododecane or 1-azidooctadecane. The potential for each of these analogues to function as tethers of lipid bilayers to Au(111) was assessed primarily by differential capacitance experiments. Deposition of a bilayer of DMPC/cholesterol (70:30) by Langmuir-Blodgett (LB) transfer followed by Langmuir-Schaefer (LS) touch to a self-assembled monolayer of the O-6’ linked analogue, diluted with 1-β-D-thioglucose, failed. This led to simplifying the target architecture to diagnose the quality of the monolayers. A monolayer of the known monosaccharide 1-octadecane-4-(6-thio-β-D-galacto-pyranosyloxymethyl)-[1,2,3]-triazole1 prepared by LB transfer was found to support a lipid monolayer deposited by LS touch and this bilayer had the lowest minimum capacitance observed of 0.9 µF/cm2. An attempt to produce a bilayer by the same method using the trisaccharide bearing the C-18 alkane chain failed and this was attributed to high water solubility, which gave rise to poor organization at the air-water interface. A self-assembled monolayer of this variant went forward to produce a poor quality bilayer with a minimum capacitance of 7.1 µF/cm2, which was the lowest value obtained for the trisaccharide series of analogues. / Natural Sciences and Engineering Research Council of Canada (NSERC)

The purpose of the immune system is to protect our bodies from infection. One way it accomplishes this task is through the presentation of foreign pathogens to NKT cells. After an antigen is presented to the T cell receptor, activated NKT cells quickly release soluble chemical signals, termed chemokines and cytokines, that modulate the response of the immune system. Due to the immunological relevance of NKT cell activation, we developed and synthesised non-natural analogs of immunostimulatory type I, II, and gamma delta NKT cell antigens. The immunological evaluations of these analogs resulted in identification of sulfatide as a gamma delta NKT cell antigen, along with the characterization of these newly discovered sulfatide-reactive gamma delta NKT cell line. During sulfatide structure activity relationship studies, a novel azido-sulfatide analog was synthesized to traffick and image sulfatide in vivo. These studies demonstrated that sulfatide accumulated in the late endosome/lysosome. In conjunction with previous studies, this observation explains the persistence of CD1d-restricted T cells with high affinity for this antigen in healthy individuals. Finally, stimulatory assays were performed on a panel of synthesized lyso-glycosylceramides. This led to the discovery of stimulatory type I NKT cell antigens, alpha-psychosine and alpha-glucopsychosine.

No / Piperacillin, a potent ß-lactam antibiotic, is effective in a large variety of Gram+ and Gram¿ bacterial infections but its administration is limited to the parenteral route as it is not absorbed when given orally. In an attempt to overcome this problem, we have synthesized a novel series of charged liposaccharide complexes of piperacillin comprising a sugar moiety derived from d-glucose conjugated to a lipoamino acid residue with varying side-chain length (cationic entity) and the piperacillin anion. A complete multiple reaction monitoring LC¿MS/MS method was developed to detect and characterize the synthesized complexes. The same method was then successfully applied to assess the in vitro apparent permeability values of the charged liposaccharide complexes in Caco-2 monolayers. / BBSRC

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Carbohydrate-protein interactions are responsible for several biological functions. While these interactions maintain high levels of specificities, the binding strength of individual carbohydrate-protein recognitions are weak, with dissociation constants (Kd) ~10-3-10-6 M. In order to increase the binding strengths meaningful to physiological functions, multivalent, clustered patches of carbohydrate ligands are required. Synthetic glycoclusters contribute in a significant manner to understand the fine details of the weak carbohydrate-protein interactions. The extent of clustering of the ligands, spatial, topological orientations and the nature of the scaffolds are prominent issues to address the carbohydrate-protein interactions in general. Chapter 1 of the Thesis presents a summary of the synthetic cluster glycosides, mechanisms and energetics of their interactions with lectins. The presence of several ligands within the molecular scaffold is not sufficient, rather there exists a critical demand on the spatial disposition of the individual ligands in the multivalent ligand system to achieve enhanced binding affinities. In order to assess the multivalent effects, influence of linkers and the spatial disposition of the ligands, a systematic study was undertaken, involving a series of the most minimal of the multivalent sugar ligand system, namely, the bivalent sugar ligands. In a programme, it was desired to study the bivalent and monovalent sugar ligand-lectin interactions in a two-dimensional membrane model system. An appropriate model system was the Langmuir monolayer formations of the sugar ligands and their recognitions of the lectins at the interface. A series of bivalent and monovalent glycolipids were thus designed and synthesized. Molecular structure of the ligands utilized to study the lectins binding behavior at the air-water interface are presented in Figure 1. The sugar density dependent lectin binding at the air-water interface caused by the glycolipids was studied in detail. Prior to lectin binding studies, the monolayer behavior of the glycolipids (GL), non-sugars (NS) and their mixtures were assessed. It was observed that the apparent molecular areas of the mixed monolayers increased with increasing percentage of the glycolipid in the mixed monolayer. Interactions of the glycolipid mixed monolayers with lectin were assessed at a constant surface pressure of 10 mN/m. The adsorption kinetics of the lectin concanavalin A (Con A) with the mixed monolayers was monitored by the surface area variation (ΔA) as a function of time. The detailed studies showed a maximum increase in ΔA of 10% of the bivalent glycolipids in the mixed monolayer and a ΔA of 20% of the monovalent glycolipids (Figure 2). With both bivalent and monovalent glycolipids, change in the area per molecule had decreased progressively with higher percentage of the glycolipids in the monolayers. On the other hand, with ethylene glycol spacers, the relative responses and the amount of bound lectin increased. Figure 2. Ligand-lectin interactions at the air-water interface as a function of the percentage of (a) bivalent glycolipids and (b) monovalent glycolipids in the mixed monolayers. To verify the specificity of these interactions, the mannopyranoside non-specific lectin, namely, wheat germ agglutinin (WGA) was tested and there were no deviations in the ΔA for various ratios of the sugar–non-sugar mixed monolayers. The study established that (i) maximal binding of the lectin to the bivalent glycolipids occurred at lower sugar densities at the interface than that for the monovalent glycolipids and (ii) the surface presenting sparsely populated sugar residues are efficient for a lectin binding. Chapter 2 presents the details of synthesis and ligand-lectin interactions at the air-water interface, relevant in the two-dimensional membrane model system. A study of the multivalent effects originating through glycolipid micelles and their lectin interactions was undertaken in another programme. The kinetic studies of the glycolipid micelles-lectin interactions were conducted with the aid of surface plasmon resonance (SPR) technique. Prior to the SPR studies, the critical micellar concentration (CMC), aggregation number and the hydrodynamic diameter of each glycolipid (GL-1 to GL-6, Figure 1) micelles were determined. The glycolipid micelles were used as the analytes on a Con A immobilized surface. The sensorgrams obtained for the interaction of the various glycolipid micelles with Con A are presented in Figure 3. Figure 3. Sensorgrams obtained for the binding of various glycolipids micelles to a Con A immobilized surface, at a constant glycolipid concentration of 250 µM. The kinetic studies of the interactions were performed and the analysis showed that the bivalent analyte model provided a better fitting for the interaction sensorgrams. The analysis revealed that the ka1/kd1 values remained largely uniform for all the glycolipids, whereas the ka2/kd2 values were about two orders of magnitude larger for the bivalent glycolipid (GL-4 to GL-6) micelle-lectin interactions than for the monovalent series (GL-1 to GL-3) (Table 1). From the SPR studies, it emerged that the additional sugar unit in the bivalent glycolipid micelles provided a favorable complexation between the sugar ligand and the lectin. Further, the glycolipid micelles mediated layer-by-layer Con A multilayer formation was also studied by SPR and atomic force microscopy (AFM) methods. Chapter 3 provides the SPR studies of glycolipid micelles-lectin interactions. A study of the monomolecular recognitions of the mono- and bivalent sugar ligands 1-8 (Figure 4) to a lectin was undertaken subsequently. The kinetic studies of the bivalent vs monovalent ligands during lectin binding were conducted by employing the SPR technique, for which the sugar ligands 1-6 were used as the analytes on a lectin coated sensor surface. Figure 4. Structures of the mono- and bivalent sugar ligands 1-8 and the NS derivative. The following observations were made from the SPR analysis. (i) Within the mono- and bivalent series, the response units increased in the series 1–3 and 4–6; (ii) the equilibrium responses were attained within 105 seconds in the monovalent ligands and (iii) the association response gradually increased for the bivalent ligands 5 and 6 and reached an equilibrium after ~3 min. An important outcome of the kinetic studies was the identification of ka and kd for the monomolecular interactions, that were distinctly different for the bivalent ligands. Specifically, the ka was significantly faster and kd was slower for bivalent sugar ligands, in comparison to the monovalent sugar ligands (Table 2). Table 2. SPR derived kinetic parameters for the interactions of sugar ligand to a Con A immobilized surface at 25 oC. Isothermal titration calorimetry (ITC) studies were also conducted, in order to correlate the functional valencies and the thermodynamic parameters. The studies were conducted at ligand concentrations much below their CMCs. The general observations from the ITC studies were that the binding site saturations were slower for the monovalent sugar ligands, in comparison to the bivalent sugar ligands. It was observed that the binding affinities of bivalent ligands 5 and 6 enhanced ~5 times higher than the monovalent ligands 2 and 3 (Table 3). The effective linker length, which allowed the sugar ligands to be functionally active, was determined to be ~15 Å and this separation was necessary for the intermolecular cross-linking formation. The dynamic light scattering (DLS) study of the bivalent ligands 5 or 6-lectin complexes showed the presence of intermolecular cross-linked complexes that existed in solution from the initial stages of the binding process. Upon realizing the nanometric diameters of the sugar ligand-lectin complex, an attempt was undertaken to visualize the complexes by transmission electron micoscopy (TEM). In TEM, 4-Con A complex exhibited particle sizes in the range of 5-10 nm, matching nearly the size of the lectin alone. On the other hand, 5–Con A and 6–Con A complexes provided sizes varying between 20¬150 nm. These particle sizes corresponded to similar aggregate sizes derived from the DLS studies. Chaper 4 describes the kinetic, thermodynamic, DLS and TEM studies of sugar ligand-lectin intearctions. Table 3. Binding stoichiometries and thermodynamic parameters of the sugar ligand-Con A interactions at 25 oC.a Ligand n Ka (x 10 -4) ΔG ΔH TΔS 1 0.91 9.14 ( ± 0.75) -6.76 -3.39 3.37 2 1.01 5.76 (± 0.80) -6.49 -3.98 2.51 3 1.09 7.06 (± 1.23) -6.61 - 3.01 3.60 4 1.10 5.75 (± 0.27) -6.49 - 6.39 0.10 5 0.50 20.6 (± 1.7) -7.59 - 12.80 -5.21 6 0.47 37. 4 (± 2. 4) -7.61 -11.54 -3.93 7 1.03 0.86 (± 0.06) -5.36 -7.9 -2.62 8 1.05 2.48 (± 0.12) -5.99 -6.3 -0.32 MeαMan 1.04 0.79 (± 0.04) -5.27 -7.83 -2.56 Ka is in the unit of M-1; ΔG, ΔH and TΔS are in the units of kcal mol-1. Errors in ΔG are ~1-4%. Errors in ΔH are in the range of 1-8%. Errors in TΔS are in the range of 1-6 %. A study was undertaken further to assess the kinetic interactions of the tumor-associated T-antigen with a lectin. Synthesis of amine-tethered T-antigen and lactose derivatives (Figure 5) were accomplished and an assessment of their kinetic interactions with lectin peanut agglutinin (PNA) was conducted. Figure 5. Structures of the amine-tethered T-antigen, lactose and mannose derivatives. The lectin PNA was used as the analyte onto the sugar ligand immobilized surfaces. It was found that the interaction with T-antigen showed higher response units than the lactose derivative (Figure 6). The kinetic studies of PNA with immobilized T-antigen and the lactose derivatives demonstrated that the binding followed a bivalent analyte model of the interaction. The T-antigen derivative interacted with the lectin and relatively faster association (ka) and a slower dissociation (kd) were observed, in comparison to the lactose derivative. The ratio of second binding kinetic constants (ka2/kd2) was observed higher than the first binding kinetic constants (ka1/kd1). Further, the ITC studies were conducted, in order to provide the thermodynamic parameters governing the lectin-T-antigen interactions. The combined approach of SPR and ITC studies showed that the T-antigen derivative exhibited a higher binding affinity to PNA than the lactose derivative. Chapter 5 presents synthesis of the T-antigen and lactose derivatives and studies of their lectin interactions. In summary, the thesis provides a detailed insight into the kinetic and thermodynamic parameters of the bivalent sugar ligand-lectin interactions, in comparison to the monovalent sugar ligands. Langmuir monolayer formation of the sugar ligands and the assessment of their lectin binding at the air-water interface demonstrated that the surface presenting sparsely populated sugar residues are efficient for a lectin binding. The kinetic studies of various glycolipid micelles-lectin interactions showed that the additional sugar unit in the bivalent glycolipid micelles provided a favorable complexation between the sugar ligand and the lectin. The detailed monomolecular kinetic studies showed that the bivalent sugar ligands underwent a faster association (kon) and a slower dissociation (koff) of the ligand-lectin complexes. The ITC studies on sugar ligand-lectin interactions led to identify not only the thermodynamic parameters, but also the influence of the hydrophobic alkyl units and the linker moieties. The DLS and TEM characterizations of sugar ligand-lectin complexes showed the status of the complexation, sizes and the morphologies. The studies were extended further to tumor associated T-antigen-lectin interactions. Overall, the Thesis establishes the most minimal multivalent sugar ligands, namely, the bivalent sugar ligand-letin interactions. The studies presented in the Thesis should be useful to design multivalent sugar ligands for highly avid lectin interactions and also to raise possibilities for the construction of defined lectin oligomers, facilitated through the multivalent sugar ligand-lectin cross-linking interactions.

Trichobilharzia spp. are avian schistosomes related to medically important human parasites of the genus Schistosoma. Penetrating cercariae are well known as causative agent of cercarial dermatitis in humans. Cercariae actively penetrate the skin of definitive hosts and transform into schistosomula. This process is preceded by cercarial tail detachment and includes emptying of penetration glands and extensive surface changes. One of these changes is the loss of highly immunogenic glycocalyx which represents a protective coat in the aquatic environment. The glycocalyx has specific composition of saccharide molecules which are bound to lipids or proteins on the membrane of cercarial tegument. There is only limited information about the mechanism of shedding. Hypotheses based on indirect evidences suggest that peptidases or (phospho)lipases from penetration glands could be involved. This work describes the changes in surface glycosylation during transformation of cercariae into schistosomula by fluorescently labelled lectins and monoclonal antibodies against Lewis X antigen. Lectins UEA-I, LTA and PNA have been chosen as markers of transformation of T. regenti. Further, our experiments have been focused on shedding of cercarial glycocalyx. During in vitro induction of penetration gland emptying and...

<p>Glycoconjugates are biologically important molecules with diverse functions. They consist of carbohydrates of varying size and complexity, attached to a non-sugar moiety as a lipid or a protein. Glycoconjugate structures are often very complex and their intricate biosynthetic pathways makes overexpression difficult. This renders the isolation of pure, structurally defined compounds from natural sources cumbersome. Therefore, to better address questions in glycobiology, synthetic glycoconjugates are an appealing alternative. In addition, synthetic methods allow for the preparation of non-natural glycoconjugates that can enhance the understanding of the influence of structural features on the biological responses.</p><p>In this thesis, synthetic methods for the preparation of glycoconjugates, especially glycolipid analogues, have been developed. These methods make use of solid-phase chemistry and are amenable to library synthesis of series of similar compounds. Solid-phase synthesis is a technique where the starting material of the reaction is attached to small plastic beads through a linker. This allows large excess of reagents to speed up the reactions and the sometimes difficult purifications of intermediate products are reduced to simple washings of the beads.</p><p>One problem with solid-phase synthesis is the difficulties to monitor the reactions and characterize the intermediate products. Gel-phase 19 F-NMR spectroscopy, using fluorinated linkers and protecting groups, is an excellent tool to overcome this problem and to monitor solid-phase synthesis of e.g. glycoconjugates. Two novel fluorinated linkers for the attachment of carboxylic acids have been developed and are presented in the thesis. These linkers can be cleaved with both acids of varying strengths and nucleophiles like hydroxide ions, and they are stable to glycosylation conditions. In addition, a novel filter reactor for solid-phase synthesis was designed. The reactor fits into an ordinary NMR spectrometer to facilitate the reaction monitoring with gel-phase 19 F-NMR spectroscopy.</p><p>The biological applications of the synthesized glycolipids were demonstrated in two different settings. The CD1d restricted binding of glycolipids carrying the monosaccharide α-GalNAc as carbohydrate could be detected on viable cells of mouse origin. CD1d is one of several antigen presenting molecules (the CD1 proteins) that presents lipids and glycolipids to circulating T-cells that in turn can initiate an immune response. The CD1 molecules are relatively sparsely investigated, and the method to measure glycolipid binding on viable cells, as described in the thesis, has the possibility to greatly enhance the knowledge of the structural requirements for CD1-binding.</p><p>Serine-based neoglycolipids with terminal carboxylic acids were used to prepare glycoconjugate arrays with covalent bonds to secondary amines on microtiter plates. Carbohydrate arrays have great possibilities to simplify the study of interactions between carbohydrates and e.g. proteins and microbes. The usefulness of the glycolipid arrays constructed in the thesis was illustrated with two lectins, RCA120 from Ricinus communis and BS-1 from Bandeiraea simplicifolia. Both lectins bound to the array of neoglycolipids in agreement with their respective specificity for galactosides.</p><p>Glycobiology is a large area of great interest and the methods described in this thesis can be used to answer a variety of glycoconjugaterelated biological questions.</p>