The α-Galactosyl Carbohydrate Epitope in Pathogenic Protozoa.

The α-gal epitope, which refers to the carbohydrate α-d-Galp-(1 → 3)-ß-d-Galp-(1 → 4)-d-GlcNAc-R, was first described in the glycoconjugates of mammals other than humans. Evolution caused a mutation that resulted in the inactivation of the α-1,3-galactosyltransferase gene. For that reason, humans produce antibodies against α-d-Galp containing glycoproteins and glycolipids of other species. We summarize here the glycoconjugates with α-d-Galp structures in Trypanosoma, Leishmania, and Plasmodium pathogenic protozoa. These were identified in infective stages of Trypanosoma cruzi and in Plasmodium sporozoites. In Leishmania, α-d-Galp is linked differently in the glycans of glycoinositolphospholipids (GIPLs). Chemically synthesized neoglycoconjugates have been proposed as diagnostic tools and as antigens for vaccines. Several syntheses reported for the α-gal trisaccharide, also called the Galili epitope, and the glycans of GIPLs found in Leishmania, the preparation of neoglycoconjugates, and the studies in which they were involved are also included in this Review.

trans-Sialylation: a strategy used to incorporate sialic acid into oligosaccharides.

Sialic acid, as a component of cell surface glycoconjugates, plays a crucial role in recognition events. Efficient synthetic methods are necessary for the supply of sialosides in enough quantities for biochemical and immunological studies. Enzymatic glycosylations obviate the steps of protection and deprotection of the constituent monosaccharides required in a chemical synthesis. Sialyl transferases with CMP-Neu5Ac as an activated donor were used for the construction of α2-3 or α2-6 linkages to terminal galactose or N-acetylgalactosamine units. trans-Sialidases may transfer sialic acid from a sialyl glycoside to a suitable acceptor and specifically construct a Siaα2-3Galp linkage. The trans-sialidase of Trypanosoma cruzi (TcTS), which fulfills an important role in the pathogenicity of the parasite, is the most studied one. The recombinant enzyme was used for the sialylation of ß-galactosyl oligosaccharides. One of the main advantages of trans-sialylation is that it circumvents the use of the high energy nucleotide. Easily available glycoproteins with a high content of sialic acid such as fetuin and bovine κ-casein-derived glycomacropeptide (GMP) have been used as donor substrates. Here we review the trans-sialidase from various microorganisms and describe their application for the synthesis of sialooligosaccharides.

The Glycan Structure of T. cruzi mucins Depends on the Host. Insights on the Chameleonic Galactose.

Trypanosoma cruzi, the protozoa that causes Chagas disease in humans, is transmitted by insects from the Reduviidae family. The parasite has developed the ability to change the structure of the surface molecules, depending on the host. Among them, the mucins are the most abundant glycoproteins. Structural studies have focused on the epimastigotes and metacyclic trypomastigotes that colonize the insect, and on the mammal trypomastigotes. The carbohydrate in the mucins fulfills crucial functions, the most important of which being the accepting of sialic acid from the host, a process catalyzed by the unique parasite trans-sialidase. The sialylation of the parasite influences the immune response on infection. The O-linked sugars have characteristics that differentiate them from human mucins. One of them is the linkage to the polypeptide chain by the hexosamine, GlcNAc, instead of GalNAc. The main monosaccharide in the mucins oligosaccharides is galactose, and this may be present in three configurations. Whereas ß-d-galactopyranose (ß-Galp) was found in the insect and the human stages of Trypanosoma cruzi, ß-d-galactofuranose (ß-Galf) is present only in the mucins of some strains of epimastigotes and α-d-galactopyranose (α-Galp) characterizes the mucins of the bloodstream trypomastigotes. The two last configurations confer high antigenic properties. In this review we discuss the different structures found and we pose the questions that still need investigation on the exchange of the configurations of galactose.

Synthesis of the hexasaccharide from Trypanosoma cruzi mucins with the Galp(1 → 2)Galf unit constructed with a superarmed thiogalactopyranosyl donor.

Hexasaccharide ß-D-Galp-(1→ 2)-[ß-D-Galp-(1 → 3)]-ß-D-Galp-(1 → 6)-[ß-D-Galp-(1 → 2)-ß-D-Galf-(1 → 4)]-D-GlcNAc (1) was found O-linked in mucins of Trypanosoma cruzi epimastigotes and metacyclic trypomatigotes. Studies on the biological pathways and functionalities of the mucin oligosaccharides are prompted in order to understand the interactions of these molecules with the insect host. Trisaccharide constituent ß-D-Galp-(1 → 2)-ß-D-Galf-(1 → 4)-D-GlcNAc was constructed from the reducing to the non-reducing end. We discuss the difficulties to introduce a Galp unit at the O-2 position of a partially protected galactofuranosyl unit which were overcome using an anchimerically superarmed donor. By this route and employing a [3 + 3] nitrilium convergent approach hexasaccharide 1 was synthesized in moderate yield.

Trypanosoma cruzi surface mucins are involved in the attachment to the Triatoma infestans rectal ampoule.

BACKGROUND: Trypanosoma cruzi, the agent of Chagas disease, is a protozoan parasite transmitted to humans by blood-sucking triatomine vectors. However, and despite its utmost biological and epidemiological relevance, T. cruzi development inside the digestive tract of the insect remains a poorly understood process. METHODS/PRINCIPLE FINDINGS: Here we showed that Gp35/50 kDa mucins, the major surface glycoproteins from T. cruzi insect-dwelling forms, are involved in parasite attachment to the internal cuticle of the triatomine rectal ampoule, a critical step leading to its differentiation into mammal-infective forms. Experimental evidence supporting this conclusion could be summarized as follows: i) native and recombinant Gp35/50 kDa mucins directly interacted with hindgut tissues from Triatoma infestans, as assessed by indirect immunofluorescence assays; ii) transgenic epimastigotes over-expressing Gp35/50 kDa mucins on their surface coat exhibited improved attachment rates (~2-3 fold) to such tissues as compared to appropriate transgenic controls and/or wild-type counterparts; and iii) certain chemically synthesized compounds derived from Gp35/50 kDa mucins were able to specifically interfere with epimastigote attachment to the inner lining of T. infestans rectal ampoules in ex vivo binding assays, most likely by competing with or directly blocking insect receptor(s). A solvent-exposed peptide (smugS peptide) from the Gp35/50 kDa mucins protein scaffolds and a branched, Galf-containing trisaccharide (Galfß1-4[Galpß1-6]GlcNAcα) from their O-linked glycans were identified as main adhesion determinants for these molecules. Interestingly, exogenous addition of a synthetic Galfß1-4[Galpß1-6]GlcNAcα derivative or of oligosaccharides containing this structure impaired the attachment of Dm28c but not of CL Brener epimastigotes to triatomine hindgut tissues; which correlates with the presence of Galf residues on the Gp35/50 kDa mucins' O-glycans on the former but not the latter parasite clone. CONCLUSION/SIGNIFICANCE: These results provide novel insights into the mechanisms underlying T. cruzi-triatomine interplay, and indicate that inter-strain variations in the O-glycosylation of Gp35/50 kDa mucins may lead to differences in parasite differentiation and hence, in parasite transmissibility to the mammalian host. Most importantly, our findings point to Gp35/50 kDa mucins and/or the Galf biosynthetic pathway, which is absent in mammals and insects, as appealing targets for the development of T. cruzi transmission-blocking strategies.

Trypanosoma cruzi trans-sialidase. A tool for the synthesis of sialylated oligosaccharides.

Cells are covered by a complex array of carbohydrates. Among them, sialosides are of key importance in intracellular adhesion, recognition and signaling. The need for structurally diverse sialosides impelled the search for efficient synthetic methods since their isolation from natural sources is a difficult task. The enzymatic approach obviates the need of a chemical synthesis for protecting or participating groups in the substrates. The trans-sialidase of Trypanosoma cruzi (TcTS) is highly stereospecific for the transfer of sialic acid from an α-sialylglycoside donor to a terminal ß-galactopyranosyl unit in the acceptor substrate to form the α-Neu5Ac-(2 → 3)-ß-D-Galp motif. The enzyme was cloned and easily available glycoproteins, e.g. fetuin, may be used as donors of sialic acid, constituting strong points for the scalability of TcTS-catalyzed reactions. This review outlines the preparative use of TcTS for the sialylation of oligosaccharides. A detailed description of the substrates used as sialic acid donors, the acceptor substrates and the methods employed to monitor the reaction is included.

Synthesis and characterization of α-d-Galp-(1 → 3)-ß-d-Galp epitope-containing neoglycoconjugates for chagas disease serodiagnosis.

The immunodominant epitope α-d-Galp-(1 → 3)-ß-d-Galp-(1 → 4)-d-GlcNAc, expressed in the mucins of the infective trypomastigote stage of Trypanosoma cruzi has been proposed for multiple clinical applications, from serodiagnosis of protozoan caused diseases to xenotransplantation or cancer vaccinology. It was previously shown that the analogue trisaccharide, with glucose in the reducing end instead of GlcNAc, was as efficient as the natural trisaccharide for recognition of chagasic antibodies. Here we describe the synthesis of α-d-Galp-(1 → 3)-ß-d-Galp-(1 → 4)-d-Glcp functionalized as the 6-aminohexyl glycoside and its conjugation to BSA using the squarate method. The conjugate of 6-aminohexyl α-d-Galp-(1 → 3)-ß-d-Galp was also prepared. Both neoglycoconjugates were recognized by serum samples of Trypanosoma cruzi-infected individuals and thus, are promising tools for the improvement of Chagas disease diagnostic applications.

Synthesis of a model trisaccharide for studying the interplay between the anti α-Gal antibody and the trans-sialidase reactions in Trypanosoma cruzi.

Trypanosoma cruzi, the etiologic agent of Chagas disease, is covered by a dense glycocalix mainly composed by glycoproteins called mucins which are also the acceptors of sialic acid in a reaction catalyzed by a trans-sialidase (TcTS). Sialylation of trypomastigote mucins protects the parasite from lysis by the anti α-Galp antibodies from serum. The TcTS is essential for the infection process since T. cruzi is unable to biosynthesize sialic acid. The enzyme specifically transfers it from a terminal ß-d-Galp unit in the host glycoconjugate to terminal ß-d-Galp units in the parasite mucins to construct the d-NeuNAc(α2→3)ß-d-Galp motif. On the other hand, although galactose is the most abundant sugar in mucins of both, the infective trypomastigotes and the insect stage epimastigotes, α-d-Galp is only present in the infective stage whereas ß-d-Galf is characteristic of the epimastigote stage of the less virulent strains. Neither α-d-Galp nor d-Galf is acceptor of sialic acid. In the mucins, some of the oligosaccharides are branched with terminal ß-d-Galp units to be able to accept sialic acid in the TcTS reaction. Based on previous reports showing that anti α-Galp antibodies only partially colocalize with sialic acid, we have undertaken the synthesis of the trisaccharide α-d-Galp(1→3)-[ß-d-Galp(1→6)]-d-Galp, the smallest structure containing both, the antigenic d-Galp(α1→3)-d-Galp unit and the sialic acid-acceptor ß-d-Galp unit. The trisaccharide was obtained as the 6-aminohexyl glycoside to facilitate further conjugation for biochemical studies. The synthetic approach involved the α-galactosylation at O-4 of a suitable precursor of the reducing end, followed by ß-galactosylation at O-6 of the same precursor and introduction of the 6-aminohexyl aglycone. The fully deprotected trisaccharide was successfully sialylated by TcTS using either 3'-sialyllactose or fetuin as donors. The product, 6-aminohexyl α-d-NeuNAc(2→3)-ß-d-Galp(1→6)-[α-d-Galp(1→3)]-ß-d-Galp, was purified and characterized.

Galactofuranose antigens, a target for diagnosis of fungal infections in humans.

The use of biomarkers for the detection of fungal infections is of interest to complement histopathological and culture methods. Since the production of antibodies in immunocompromised patients is scarce, detection of a specific antigen could be effective for early diagnosis. D-Galactofuranose (Galf) is the antigenic epitope in glycoconjugates of several pathogenic fungi. Since Galf is not biosynthesized by mammals, it is an attractive candidate for diagnosis of infection. A monoclonal antibody that recognizes Galf is commercialized for detection of aspergillosis. The linkage of Galf in the natural glycans and the chemical structures of the synthesized Galf-containing oligosaccharides are described in this paper. The oligosaccharides could be used for the synthesis of artificial carbohydrate-based antigens, not enough exploited for diagnosis.

Multivalent sialylation of ß-thio-glycoclusters by Trypanosoma cruzi trans sialidase and analysis by high performance anion exchange chromatography.

The synthesis of multivalent sialylated glycoclusters is herein addressed by a chemoenzymatic approach using the trans-sialidase of Trypanosoma cruzi (TcTS). Multivalent ß-thio-galactopyranosides and ß-thio-lactosides were used as acceptor substrates and 3'-sialyllactose as the sialic acid donor. High performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) was shown to be an excellent technique for the analysis of the reaction products. Different eluting conditions were optimized to allow the simultaneous resolution of the sialylated species, as well as their neutral precursors. The TcTS efficiently transferred sialyl residues to di, tri, tetra and octa ß-thiogalactosides. In the case of an octavalent thiolactoside, up to six polysialylated compounds could be resolved. Preparative sialylation reactions were performed using the tetravalent and octavalent acceptor substrates. The main sialylated derivatives could be unequivocally assigned by MALDI mass spectrometry. Inhibition of the transfer to the natural substrate, N-acetyllactosamine, was also studied. The octalactoside caused 82 % inhibition of sialic acid transfer when we used equimolar concentrations of donor, acceptor and inhibitor.

Synthesis of the O-linked hexasaccharide containing ß-D-Galp-(1→2)-D-Galf in Trypanosoma cruzi mucins. Differences on sialylation by trans-sialidase of the two constituent hexasaccharides.

The hexasaccharide ß-D-Galp-(1→2)-[ß-D-Galp-(1→3)]-ß-D-Galp-(1→6)-[ß-D-Galp(1→2)-ß-D-Galf(1→4)]-D-GlcNAc (10) and its ß-D-Galf-(1→2)-ß-D-Galf containing isomer (7) are the largest carbohydrates in mucins of some strains of Trypanosoma cruzi. The terminal ß-D-Galp units are sites of sialylation by the parasite trans-sialidase. Hexasaccharide 10 was chemically synthesized for the first time by a [3+3] nitrilium based convergent approach, using the trichloroacetimidate method of glycosylation. The (1)H NMR spectrum of its alditol was identical to the spectrum of the product released by ß-elimination from the parasite mucin. The trans-sialylation reaction studied on the benzyl glycoside of 10 showed two monosialylated products whose relative abundance changed with time. On the other hand, only one product was produced by sialylation of the benzyl glycoside of 7. A preparative synthesis of the latter and spectroscopic analysis of the product unequivocally established the sialylation site at the less hindered (1→3)-linked galactopyranose.

Carbohydrate PEGylation, an approach to improve pharmacological potency.

Conjugation with polyethylene glycol (PEG), known as PEGylation, has been widely used to improve the bioavailability of proteins and low molecular weight drugs. The covalent conjugation of PEG to the carbohydrate moiety of a protein has been mainly used to enhance the pharmacokinetic properties of the attached protein while yielding a more defined product. Thus, glycoPEGylation was successfully applied to the introduction of a PEGylated sialic acid to a preexisting or enzymatically linked glycan in a protein. Carbohydrates are now recognized as playing an important role in host-pathogen interactions in protozoal, bacterial and viral infections and are consequently candidates for chemotherapy. The short in vivo half-life of low molecular weight glycans hampered their use but methods for the covalent attachment of PEG have been less exploited. In this review, information on the preparation and application of PEG-carbohydrates, in particular multiarm PEGylation, is presented.

Synthesis of divalent ligands of ß-thio- and ß-N-galactopyranosides and related lactosides and their evaluation as substrates and inhibitors of Trypanosoma cruzi trans-sialidase.

In this work we describe the synthesis of mono- and divalent ß-N- and ß-S-galactopyranosides and related lactosides built on sugar scaffolds and their evaluation as substrates and inhibitors of the Trypanosoma cruzi trans-sialidase (TcTS). This enzyme catalyzes the transfer of sialic acid from an oligosaccharidic donor in the host, to parasite ßGalp terminal units and it has been demonstrated that it plays an important role in the infection. Herein, the enzyme was also tested as a tool for the chemoenzymatic synthesis of sialic acid containing glycoclusters. The transfer reaction of sialic acid was performed using a recombinant TcTS and 3'-sialyllactose as sialic acid donor, in the presence of the acceptor having ßGalp non reducing ends. The products were analyzed by high performance anion exchange chromatography with pulse amperometric detection (HPAEC-PAD). The ability of the different S-linked and N-linked glycosides to inhibit the sialic acid transfer reaction from 3'-sialyllactose to the natural substrate N-acetyllactosamine, was also studied. Most of the substrates behaved as good acceptors and moderate competitive inhibitors. A di-N-lactoside showed to be the strongest competitive inhibitor among the compounds tested (70% inhibition at equimolar concentration). The usefulness of the enzymatic trans-sialylation for the preparation of sialylated ligands was assessed by performing a preparative sialylation of a divalent substrate, which afforded the monosialylated compound as main product, together with the disialylated glycocluster.

Synthesis of a derivative of α-D-Glcp(1->2)-D-Galf suitable for further glycosylation and of α-D-Glcp(1->2)-D-Gal, a disaccharide fragment obtained from varianose.

The presence of galactofuranoyl units in infectious microorganisms has prompted the study of the metabolic pathways involved in their incorporation in glycans. Although much progress has been made with respect to the biosynthesis of ß-D-Galf-containing glycoconjugates, the mechanisms by which α-D-Galf units are incorporated remain unclear. Penicillium varians is a non-pathogenic fungus that produces varianose, a polysaccharide containing both α- and ß-D-Galf units, which can be used as a model for biosynthetic studies on α-D-Galf incorporation. Synthetic oligosaccharide fragments related to varianose are useful as potential substrates or standards for characterization of the α-galactofuranosyl transferases. In this paper we report a straightforward procedure for the synthesis of α-D-Glcp(1→2)-D-Gal (1) and the use of this compound to monitor the natural disaccharide released from varianose by mild acid degradation. The synthesis, performed by the glycosylaldonolactone approach, involved a glucosylgalactofuranose derivative, suitable for the synthesis of higher oligosaccharides with an internal D-Galf.

Synthesis of the O-linked hexasaccharide containing ß-D-Galf-(1→2)-ß-D-Galf in Trypanosoma cruzi mucins.

The hexasaccharide ß-D-Galp-(1→2)-[ß-D-Galp-(1→3)]-ß-D-Galp-(1→6)-[ß-D-Galf(1→2)-ß-D-Galf(1→4)]-D-GlcNAc (1) is the largest carbohydrate structure released as alditol by reductive ß-elimination from mucins of some strains of T. cruzi. The terminal ß-D-Galp units are sites of sialylation by trans-sialidase which transfers sialic acid from the host to the parasite. Hexasaccharide 1 was synthesized by a [3 + 3]-convergent strategy based on a nitrile assisted glycosylation, using the trichloroacetimidate method. The ß-D-Galf-(1→2)-ß-D-Galf-D-GlcNAc synthon was sequentially constructed from the reducing end to the non-reducing end employing benzyl α-D-galactofuranoside as starting material for the internal Galf unit. The choice of this novel precursor, obtained in one-reaction step from galactose, allowed the introduction of an orthogonal and participating levulinoyl group at O-2. Thus, the diastereoselective construction of the Galf-ß(1→4)-GlcNAc linkage by the trichloroacetimidate method of glycosylation was achieved. The (1)H NMR spectrum of alditol 2 was identical to the product released by ß-elimination from the parasite mucin.

Improved bioavailability of inhibitors of Trypanosoma cruzi trans-sialidase: PEGylation of lactose analogs with multiarm polyethyleneglycol.

The trans-sialidase of Trypanosoma cruzi (TcTS) catalyzes the transfer of sialic acid from host glycoconjugates to terminal ß-galactopyranosides in the mucins of the parasite. During infection, the enzyme is actively shed by the parasite to the bloodstream inducing hematological alterations. Lactitol prevents cell apoptosis caused by the TcTS, although it is rapidly eliminated from the circulatory system. Linear polyethyleneglycol (PEG) conjugates of lactose analogs were prepared but their clearance from blood was still quite fast. With the aim of improving their circulating half-lives in vivo, we now synthesized covalent conjugates of eight-arm PEG. The star-shape of these conjugates allows an increase in the molecular weight together with the loading of the active sugar. Two approaches were used for PEGylation of disaccharide derivatives containing ß-D-Galp as the non-reducing unit. (1) Amide formation between benzyl ß-D-galactopyranosyl-(1→6)-2-amino-2-deoxy-α-D-glucopyranoside and a succinimide-activated PEG. (2) Conjugation of lactobionolactone with amino end-functionalized PEG. Two 8-arm PEG derivatives (20 and 40 kDa) were used for each sugar. Substitution of all arms was proved by (1)H nuclear magnetic resonance (NMR) spectroscopy. The bioavailability of the conjugates in mice plasma was considerably improved with respect to the 5 kDa linear PEG conjugates retaining their inhibitory properties.

Trans-sialidase and mucins of Trypanosoma cruzi: an important interplay for the parasite.

A dense glycocalix covers the surface of Trypanosoma cruzi, the agent of Chagas disease. Sialic acid in the surface of the parasite plays an important role in the infectious process, however, T. cruzi is unable to synthesize sialic acid or the usual donor CMP-sialic acid. Instead, T. cruzi expresses a unique enzyme, the trans-sialidase (TcTS) involved in the transfer of sialic acid from host glycoconjugates to mucins of the parasite. The mucins are the major glycoproteins in the insect stage epimastigotes and in the infective trypomastigotes. Both, the mucins and the TcTS are anchored to the plasma membrane by a glycosylphosphatidylinositol anchor. Thus, TcTS may be shed into the bloodstream of the mammal host by the action of a parasite phosphatidylinositol-phospholipase C, affecting the immune system. The composition and structure of the sugars in the parasite mucins is characteristic of each differentiation stage, also, interstrain variations were described for epimastigote mucins. This review focus on the characteristics of the interplay between the trans-sialidase and the mucins of T. cruzi and summarizes the known carbohydrate structures of the mucins.

Inositolphosphoceramide metabolism in Trypanosoma cruzi as compared with other trypanosomatids.

Chagas disease is caused by Trypanosoma cruzi and is endemic to North, Central and South American countries. Current therapy against this disease is only partially effective and produces adverse side effects. Studies on the metabolic pathways of T. cruzi, in particular those with no equivalent in mammalian cells, might identify targets for the development of new drugs. Ceramide is metabolized to inositolphosphoceramide (IPC) in T. cruzi and other kinetoplastid protists whereas in mammals it is mainly incorporated into sphingomyelin. In T. cruzi, in contrast to Trypanosoma brucei and Leishmania spp., IPC functions as lipid anchor constituent of glycoproteins and free glycosylinositolphospholipids (GIPLs). Inhibition of IPC and GIPLs biosynthesis impairs differentiation of trypomastigotes into the intracellular amastigote forms. The gene encoding IPC synthase in T. cruzi has been identified and the enzyme has been expressed in a cell-free system. The enzyme involved in IPC degradation and the remodelases responsible for the incorporation of ceramide into free GIPLs or into the glycosylphosphatidylinositols anchoring glycoproteins, and in fatty acid modifications of these molecules of T. cruzi have been understudied. Inositolphosphoceramide metabolism and remodeling could be exploited as targets for Chagas disease chemotherapy.

Synthesis of arabinofuranose branched galactofuran tetrasaccharides, constituents of mycobacterial arabinogalactan.

Mycolyl-arabinogalactan (mAG) complex is a major component of the cell wall of Mycobacterium tuberculosis, the causative agent of tuberculosis disease. Due to the essentiality of the cell wall for mycobacterium viability, knowledge of the biosynthesis of the arabinogalactan is crucial for the development of new therapeutic agents. In this context, we have synthesized two new branched arabinogalactafuranose tetrasaccharides, decenyl ß-D-Galf-(1→5)-ß-D-Galf-(1→6)[α-D-Araf(1→5)]-ß-D-Galf (1) and decenyl ß-D-Galf-(1→6)-[α-D-Araf-(1→5)]-ß-D-Galf-(1→5)-ß-D-Galf (2), as interesting tools for arabinofuranosyl transferase studies. The aldonolactone strategy for the introduction of the internal d-Galf was employed, allowing the construction of oligosaccharides from the non-reducing to the reducing end. Moreover, a one-pot procedure was developed for the synthesis of trisaccharide lactone 21, precursor of 2, which involved a glycosylation-deprotection-glycosylation sequence, through the use of TMSOTf as catalyst of the trichloroacetimidate method as well as promoter of TBDMS deprotection.

Synthesis of PEGylated lactose analogs for inhibition studies on T.cruzi trans-sialidase.

Trypanosoma cruzi, the agent of Chagas disease, expresses a unique enzyme, the trans-sialidase (TcTS) involved in the transfer of sialic acid from host glycoconjugates to mucins of the parasite. The enzyme is shed to the medium and may affect the immune system of the host. We have previously described that lactose derivatives effectively inhibited the transfer of sialic acid to N-acetyllactosamine. Lactitol also prevented the apoptosis caused by the TcTS, although it is rapidly eliminated from the circulatory system. In this paper we report covalent conjugation of polyethylene glycol (PEG) with lactose, lactobionolactone and benzyl beta-D-galactopyranosyl-(1-->6)-2-amino-2-deoxy-alpha-D-glucopyranoside (1) with the hope to improve the bioavailability, though retaining their inhibitory properties. Different conjugation methods have been used and the behavior of the PEGylated products in the TcTS reaction was studied.