Synthesis of di- to hexasaccharide 1,2-linked beta-mannopyranan oligomers, a terminal S-linked tetrasaccharide congener and the corresponding BSA glycoconjugates

Chemical Synthesis and Antigenicity Evaluation of an Aminoglycoside Trisaccharide Repeating Unit of Pseudomonas aeruginosa Serotype O5 O-Antigen Containing a Rare Dimeric-ManpN3NA

Pseudomonas aeruginosa bacteria are becoming increasingly resistant against multiple antibiotics. Therefore, the development of vaccines to prevent infections with these bacteria is an urgent medical need. While the immunological activity of lipopolysaccharide O-antigens in P. aeruginosa is well-known, the specific protective epitopes remain unidentified. Herein, we present the first chemical synthesis of highly functionalized aminoglycoside trisaccharide 1 and its acetamido derivative 2 found in the P. aeruginosa serotype O5 O-antigen. The synthesis of the trisaccharide targets is based on balancing the reactivity of disaccharide acceptors and monosaccharide donors. Glycosylations were analyzed by quantifying the reactivity of the hydroxyl group of the disaccharide acceptor using the orbital-weighted Fukui function and dual descriptor. The stereoselective formation of 1,2-cis-α-fucosylamine linkages was achieved through a combination of remote acyl participation and reagent modulation. The simultaneous SN2 substitution of azide groups at C2' and C2″ enabled the efficient synthesis of 1,2-cis-β-linkages for both 2,3-diamino-D-mannuronic acids. Through a strategic orthogonal modification, the five amino groups on target trisaccharide 1 were equipped with a rare acetamidino (Am) and four acetyl (Ac) groups. Glycan microarray analyses of sera from patients infected with P. aeruginosa indicated that trisaccharides 1 and 2 are key antigenic epitopes of the serotype O5 O-antigen. The acetamidino group is not an essential determinant of antibody binding. The β-D-ManpNAc3NAcA residue is a key motif for the antigenicity of serotype O5 O-antigen. These findings serve as a foundation for the development of glycoconjugate vaccines targeting P. aeruginosa serotype O5.

Simple Synthesis of 1,2-Dideoxy-2-Vinyl Carbohydrates by Tin-Free Radical Reactions of Xanthates

Vinyl-substituted carbohydrates have been synthesized from glycals derived from hexoses and pentoses. Key step is the radical reaction of xanthates in the presence of triethylborane, a non-toxic reagent. The mechanism has been investigated by isolation of various side products, which speak for a reversibility of the cyclopropylmethyl radical ring-opening. Compared to reactions with tributyltin hydride, higher regioselectivities in favor of the 2-vinyl-substituted sugars have been obtained. Yields are slightly lower with triethylborane, but all products have been isolated in analytically pure form. The new reaction is applicable to benzyl- and silyl-protected carbohydrates, which makes free sugars accessible as well. Overall, more than 15 1,2-dideoxy-2-vinyl carbohydrates have been synthesized from simple precursors in only few steps.

Direct β-Mannosylation of Primary Alcohol Acceptors: Trisaccharide Iteration Assembly of β-1,6-Oligomannosides Corresponding to Kakelokelose

Gold(I)-catalyzed stereoselective β-glycosylation of primary alcohols is achieved using the orthogonally protected mannosyl α-ortho-hexynylbenzoate (OABz) donors devoid of 4,6-O-tethering groups used in conventionally constructing β-mannosidic bonds. The potential of this methodology is showcased by the first assembly of β-1,6-tri/hexa-/nonamannosides and related sulfated congeners through a convergent strategy. The synthesis features the stereocontrolled β-glycosylation of α-trimannosyl OABz donors and the late-stage sulfonation. This work is expected to expedite the preparation of β-1,6-mannans and functionalized derivatives.

A Neoglycoprotein-Immobilized Fluorescent Magnetic Bead Suspension Multiplex Array for Galectin-Binding Studies

Carbohydrate-protein conjugates have diverse applications. They have been used clinically as vaccines against bacterial infection and have been developed for high-throughput assays to elucidate the ligand specificities of glycan-binding proteins (GBPs) and antibodies. Here, we report an effective process that combines highly efficient chemoenzymatic synthesis of carbohydrates, production of carbohydrate-bovine serum albumin (glycan-BSA) conjugates using a squarate linker, and convenient immobilization of the resulting neoglycoproteins on carboxylate-coated fluorescent magnetic beads for the development of a suspension multiplex array platform. A glycan-BSA-bead array containing BSA and 50 glycan-BSA conjugates with tuned glycan valency was generated. The binding profiles of six plant lectins with binding preference towards Gal and/or GalNAc, as well as human galectin-3 and galectin-8, were readily obtained. Our results provide useful information to understand the multivalent glycan-binding properties of human galectins. The neoglycoprotein-immobilized fluorescent magnetic bead suspension multiplex array is a robust and flexible platform for rapid analysis of glycan and GBP interactions and will find broad applications.

Glycan Array Evaluation of Synthetic Epitopes between the Capsular Polysaccharides from Streptococcus pneumoniae 19F and 19A

Vaccination represents the most effective way to prevent invasive pneumococcal diseases. The glycoconjugate vaccines licensed so far are obtained from capsular polysaccharides (CPSs) of the most virulent serotypes. Protection is largely limited to the specific vaccine serotypes, and the continuous need for broader coverage to control the outbreak of emerging serotypes is pushing the development of new vaccine candidates. Indeed, the development of efficacious vaccine formulation is complicated by the high number of bacterial serotypes with different CPSs. In this context, to simplify vaccine composition, we propose the design of new saccharide fragments containing chemical structures shared by different serotypes as cross-reactive and potentially cross-protective common antigens. In particular, we focused on Streptococcus pneumoniae (Sp) 19A and 19F. The CPS repeating units of Sp 19F and 19A are very similar and share a common structure, the disaccharide ManNAc-β-(1→4)-Glc (A-B). Herein, we describe the synthesis of a small library of compounds containing different combinations of the common 19F/19A disaccharide. The six new compounds were tested with a glycan array to evaluate their recognition by antibodies in reference group 19 antisera and factor reference antisera (reacting against 19F or 19A). The disaccharide A-B, phosphorylated at the upstream end, emerged as a hit from the glycan array screening because it is strongly recognized by the group 19 antisera and by the 19F and 19A factor antisera, with similar intensity compared with the CPSs used as controls. Our data give a strong indication that the phosphorylated disaccharide A-B can be considered a common epitope among different Sp 19 serotypes.

Progress and challenges in the synthesis of sequence controlled polysaccharides

The sequence, length and substitution of a polysaccharide influence its physical and biological properties. Thus, sequence controlled polysaccharides are important targets to establish structure-properties correlations. Polymerization techniques and enzymatic methods have been optimized to obtain samples with well-defined substitution patterns and narrow molecular weight distribution. Chemical synthesis has granted access to polysaccharides with full control over the length. Here, we review the progress towards the synthesis of well-defined polysaccharides. For each class of polysaccharides, we discuss the available synthetic approaches and their current limitations.

Total Synthesis of Phospholipomannan of Candida albicans

First, total synthesis of the cell surface phospholipomannan anchor [β-Manp-(1 → 2)-β-Manp]_n-(1 → 2)-β-Manp-(1 → 2)-α-Manp-1 → P-(O → 6)-α-Manp-(1 → 2)-Inositol-1-P-(O → 1)-phytoceramide of Candida albicans is reported. The target phospholipomannan (PLM) anchor poses synthetic challenges such as the unusual kinetically controlled (1 → 2)-β-oligomannan domain, anomeric phosphodiester, and unique phytoceramide lipid tail linked to the glycan through a phosphate group. The synthesis of PLM anchor was accomplished using a convergent block synthetic approach using three main appropriately protected building blocks: (1 → 2)-β-tetramannan repeats, pseudodisaccharide, and phytoceramide-1-H-phosphonate. The most challenging (1 → 2)-β-tetramannan domain was synthesized in one pot using the preactivation method. The phytoceramide-1-H-phosphonate was synthesized through an enantioselective A³ three-component coupling reaction. Finally, the phytoceramide-1-H-phosphonate moiety was coupled with pseudodisaccharide followed by deacetylation to produce the acceptor, which on subsequent coupling with tetramannosyl-H-phosphonate provided the fully protected PLM anchor. Final deprotection was successfully achieved by Pearlman's hydrogenation.

Synthesis of glycocluster-containing conjugates for a vaccine against cholera

The glycocluster-containing conjugates for a vaccine against cholera showed immunoreactivity comparable to conventional conjugates.

Synthesis and biological evaluation of a trisaccharide repeating unit derivative of Streptococcus pneumoniae 19A capsular polysaccharide

Streptococcus pneumoniae (SP) is a common human pathogen associated with a broad spectrum of diseases and it is still a leading cause of mortality and morbidity worldwide, especially in children. Moreover, SP is increasingly associated with drug resistance. Vaccination against the pathogen may thus represent an important strategy to overcome its threats to human health. In this context, revealing the molecular determinants of SP immunoreactivity may be relevant for the development of novel molecules with therapeutic perspectives as vaccine components. Serogroup 19 comprises the immune-cross reactive types 19F, 19A, 19B and 19C and it accounts for a high percentage of invasive pneumococcal diseases, mainly caused by serotypes 19F and 19A. Herein, we report the synthesis and biological evaluation of an aminopropyl derivative of the trisaccharide repeating unit of SP 19A. We compare two different synthetic strategies, based on different disconnections between the three monosaccharides which make up the final trisaccharide, to define the best approach for the preparation of the trisaccharide. Synthetic accessibility to the trisaccharide repeating unit lays the basis for the development of more complex biopolymer as well as saccharide conjugates. We also evaluate the binding affinity of the trisaccharide for anti-19A and anti-19F sera and discuss the relationship between the chemical properties of the trisaccharide unit and biological activity.

Stereodivergent Mannosylation Using 2- O-( ortho-Tosylamido)benzyl Group

We report a novel strategy for obtaining both anomers from a single mannosyl donor equipped with a C2- o-TsNHbenzyl ether (2- O-TAB) by switching reaction conditions. In particular, the formation of various β-mannosides was achieved with high selectivity by using a mannosyl phosphite in the presence of ZnI₂.

Conjugation of carbohydrates to proteins using di(triethylene glycol monomethyl ether) squaric acid ester revisited

Properties of di(triethylene glycol monomethyl ether) squarate relevant to conjugation of carbohydrates to proteins have been reinvestigated and compared with those of dimethyl squarate. It is concluded that the commercially available, crystalline dimethyl squarate remains the most convenient and efficient reagent for conjugation of amine-containing carbohydrates to proteins by a two-step or one-pot conjugation protocol.

Hydrogenolytic cleavage of naphthylmethyl ethers in the presence of sulfides

With the aid of a series of model thioether or thioglycoside containing polyols protected with combinations of benzyl ethers and 2-naphthylmethyl ethers it is demonstrated that the latter are readily cleaved selectively under hydrogenolytic conditions in the presence of the frequently catalyst-poisoning sulfides. These results suggest the possibility of employing 2-naphthylmethyl ethers in place of benzyl ethers in synthetic schemes when hydrogenolytic deprotection is anticipated in the presence of thioether type functionality.

Protection against Experimental Melioidosis with a Synthetic manno-Heptopyranose Hexasaccharide Glycoconjugate

Melioidosis is an emerging infectious disease caused by Burkholderia pseudomallei and is associated with high morbidity and mortality rates in endemic areas. Antibiotic treatment is protracted and not always successful; even with appropriate therapy, up to 40% of individuals presenting with melioidosis in Thailand succumb to infection. In these circumstances, an effective vaccine has the potential to have a dramatic impact on both the scale and the severity of disease. Currently, no vaccines are licensed for human use. A leading vaccine candidate is the capsular polysaccharide consisting of a homopolymer of unbranched 1→3 linked 2-O-acetyl-6-deoxy-β-d-manno-heptopyranose. Here, we present the chemical synthesis of this challenging antigen using a novel modular disaccharide assembly approach. The resulting hexasaccharide was coupled to the nontoxic H_c domain of tetanus toxin as a carrier protein to promote recruitment of T-cell help and provide a scaffold for antigen display. Mice immunized with the glycoconjugate developed IgM and IgG responses capable of recognizing native capsule, and were protected against infection with over 120 × LD₅₀ of B. pseudomallei strain K96243. This is the first report of the chemical synthesis of an immunologically relevant and protective hexasaccharide fragment of the capsular polysaccharide of B. pseudomallei and serves as the rational starting point for the development of an effective licensed vaccine for this emerging infectious disease.

Synthetic investigation toward apigenin 5-O-glycoside camellianin B as well as the chemical structure revision

The first total synthesis of the proposed and authentic structures of camellianin B were achieved, based on which the chemical structures of camellianins A and B were revised.

Automated Solution-Phase Synthesis of β-1,4-Mannuronate and β-1,4-Mannan

The first automated solution-phase synthesis of β-1,4-mannuronate and β-1,4-mannan oligomers has been accomplished by using a β-directing C-5 carboxylate strategy. By utilizing fluorous-tag assisting purification after repeated reaction cycles, β-1,4-mannuronate was synthesized up to a hexasaccharide with limited loading of a glycosyl donor (up to 3.5 equiv) for each glycosylation cycle due to the homogeneous solution-phase reaction condition. After a global reduction of the uronates, the β-1,4-mannan hexasaccharide was obtained, thereby demonstrating a new approach to β-mannan synthesis.

Synthesis of a 1,3 β-glucan hexasaccharide designed to target vaccines to the dendritic cell receptor, Dectin-1

Transformation of 3-O-benzyl-1,2:5,6-di-O-isopropylidene-α-D-glucofuranose into 2,4,6-tri-O-benzoyl-3-O-benzyl glucopyranosyl imidate proceeded efficiently via crystalline benzyl and per-benzoylated derivatives. This imidate glycosylated di-O-isopropylidene-α-D-glucofuranose in high yield and glycosylation of the disaccharide after removal of the 3'-O-benzyl ether afforded the β1,3 linked trisaccharide in excellent yield. Di- and trisaccharides imidates were readily prepared from the furanose terminated glycosylation products but both were unreactive in glycosylation reaction with the debenzylated di- and trisaccharide alcohols. The 3'-O-benzyl perbenzoylated disaccharide pyranose derivative could be selectively debenzoylated and converted to the corresponding perbenzoylated 4,6:4',6'-di-O-benzylidene derivative. Lewis acid catalyzed glycosidation gave the selectively protected disaccharide ethylthioglycoside in good overall yield. Glycosidation of this thioglycoside donor with 5-methoxycarbonylpentanol gave the disaccharide tether glycoside and after catalytic removal of benzyl ether the resulting disaccharide alcohol was glycosylated by the thioglycoside in a 2+2 reaction to yield a tetrasaccharide. Repetition of selective deprotection of the terminal 3-O-benzyl ether followed by glycosylation by the disaccharide thioglycoside gave a protected hexasaccharide. Hydrogenolysis of this hexasaccharide followed by transesterification and second hydrogenolysis to remove a residual benzyl group gave the target hexasaccharide glycoside 1 as a Dectin-1 ligand functionalized to permit covalent attachment to glycoconjugate vaccines and thereby facilitate improved antigen processing by dendritic cells.

Synthetic and immunological studies of N-acyl modified S-linked STn derivatives as anticancer vaccine candidates

N-Modified S-linked STn glycoconjugates significantly stimulated the production of IgG antibodies capable of recognizing the naturally occurring STn antigen.

Synthesis of a Candida albicans tetrasaccharide spanning the β1,2-mannan phosphodiester α-mannan junction

The cell wall phosphomannan of Candida species is a complex N-linked glycoprotein with a glycan chain containing predominantly an α-linked mannose backbone with α-mannose branches. A minor β-mannan component is attached to the branches either via a glycosidic bond (acid stable β-mannan) or a phosphodiester bond (acid-labile β-mannan). The α-mannan residues of the cell wall phosphomannan do not afford protective antibody, while the β-mannan portion is a protective antigen and has become an attractive target as the key epitope of a conjugate vaccine. We report the first synthesis of a tetrasaccharide 1 consisting of a β1,2-mannopyranosyl trisaccharide linked via a phosphodiester to methyl α-mannopyranoside. This encompasses the attachment site of the acid labile β-mannan to the α-mannan component of the cell wall phosphomannan. The trisaccharide was formed by an iterative process to first create a β-glucopyranoside linkage and then epimerize the C-2 center via an oxidation-reduction sequence. The phosphate diester linkage was accessed via an anomeric H-phosphonate. The binding of phosphomannan fragment 1 with the protective antibody C3.1 has been evaluated and compared with a β-mannotrioside in hapten inhibition experiments. The observed activities are rationalized with a model for docked in the binding site of C3.1.

Molecular recognition of Candida albicans (1->2)-β-mannan oligosaccharides by a protective monoclonal antibody reveals the immunodominance of internal saccharide residues

A self-consistent model of β-mannan oligosaccharides bound to a monoclonal antibody, C3.1, that protects mice against Candida albicans has been developed through chemical mapping, NMR spectroscopic, and computational studies. This antibody optimally binds di- and trisaccharide epitopes, whereas larger oligomers bind with affinities that markedly decrease with increasing chain length. The (1→2)-β-linked di-, tri-, and tetramannosides bind in helical conformations similar to the solution global minimum. Antibody recognition of the di- and trisaccharide is primarily dependent on the mannose unit at the reducing end, with the hydrophobic face of this sugar being tightly bound. Recognition of a tetrasaccharide involves a frameshift in the ligand interaction, shown by strong binding of the sugar adjacent to the reducing end. We show that frameshifting may also be deliberately induced by chemical modifications. Molecular recognition patterns similar to that of mAb C3.1, determined by saturation transfer difference-NMR, were also observed in polyclonal sera from rabbits immunized with a trisaccharide glycoconjugate. The latter observation points to the importance of internal residues as immunodominant epitopes in (1→2)-β-mannans and to the viability of a glycoconjugate vaccine composed of a minimal length oligosaccharide hapten.

Synthesis of Neoglycoconjugates Containing 4-Amino-4-deoxy-l-arabinose Epitopes Corresponding to the Inner Core of Burkholderia and Proteus Lipopolysaccharides

Disaccharides that contain 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) and d-glycero-d-talo-oct-2-ulosonic acid (Ko) substituted at the 8-position by 4-amino-4-deoxy-β-l-arabinopyranosyl (Ara4N) residues have been prepared. Coupling an N-phenyltrifluoroacetimidate-4-azido-4-deoxy-l-arabinosylglycosyl donor to acetyl-protected allyl glycosides of Kdo and Ko afforded anomeric mixtures of disaccharide products in 74 and 90 % yield, respectively, which were separated by chromatography. Further extension of an intermediate Ara4N-(1→8)-Kdo disaccharide acceptor, which capitalized on a regioselective glycosylation with a Kdo bromide donor under Helferich conditions, afforded the branched trisaccharide α-Kdo-(2→4)[β-l-Ara4N-(1→8)]-α-Kdo derivative. Deprotection of the protected di- and trisaccharide allyl glycosides was accomplished by TiCl₄-promoted benzyl ether cleavage followed by the removal of ester groups and reduction of the azido group with thiol or Staudinger reagents, respectively. The reaction of the anomeric allyl group with 1,3-propanedithiol under radical conditions afforded the thioether-bridged spacer glycosides, which were efficiently coupled to maleimide-activated bovine serum albumin. The neoglycoconjugates serve as immunoreagents with specificity for inner core epitopes of Burkholderia and Proteus lipopolysaccharides.

Carbohydrate vaccines: developing sweet solutions to sticky situations?

Recent technological advances in glycobiology and glycochemistry are paving the way for a new era in carbohydrate vaccine design. This is enabling greater efficiency in the identification, synthesis and evaluation of unique glycan epitopes found on a plethora of pathogens and malignant cells. Here, we review the progress being made in addressing challenges posed by targeting the surface carbohydrates of bacteria, protozoa, helminths, viruses, fungi and cancer cells for vaccine purposes.

Synthesis of 3,6-branched oligomannoside fragments of the mannan from Candida albicans cell wall corresponding to the antigenic factor 4

3-Aminopropyl glycosides of 3,6-branched penta- and hexamannoside fragments of the cell wall mannan from Candida albicans, corresponding to the antigenic factor 4, have been synthesized. Subsequent coupling of both oligosaccharides with BSA using the squarate procedure provided corresponding neoglycoconjugates.

Synthesis of a heptasaccharide fragment of the mannan from Candida guilliermondii cell wall and its conjugate with BSA

The 3-aminopropyl glycoside of a heptasaccharide fragment of the cell wall mannan from Candida guilliermondii 18, which corresponds to the antigenic Factor 9, has been synthesized by a convergent approach based on glycosylation of a tetrasaccharide acceptor with a trisaccharide donor as the key step to give a protected heptasaccharide 17. Subsequent two-step deprotection of 17 afforded the heptamannoside 18, which was then conjugated with BSA using the squarate procedure.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update covering the period 2001-2002

This review is the second update of the original review on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates that was published in 1999. It covers fundamental aspects of the technique as applied to carbohydrates, fragmentation of carbohydrates, studies of specific carbohydrate types such as those from plant cell walls and those attached to proteins and lipids, studies of glycosyl-transferases and glycosidases, and studies where MALDI has been used to monitor products of chemical synthesis. Use of the technique shows a steady annual increase at the expense of older techniques such as FAB. There is an increasing emphasis on its use for examination of biological systems rather than on studies of fundamental aspects and method development and this is reflected by much of the work on applications appearing in tabular form.

Glucuronic acid-based ulosyl donors for introducing α-d-GlcA and β-d-ManA units

Practical protocols are described for a five-step conversion of D-glucuronolactone into alpha-D-arabino-2-ketoglucuronyl bromides, which due to their alpha-selective or beta-specific glycosidation, and gluco- or manno-specific carbonyl reductions of the glucurono-2-ulosides formed, are expedient indirect donor substrates for the efficient introduction of alpha-D-GlcA or beta-D-ManA residues.

Convergent synthesis of a beta-(1-->3)-mannohexaose

An as yet unknown beta-(1-->3)-mannohexaose has been synthesized by a block route involving the coupling of two trisaccharides. Comparison of three closely related attempted mannohexaose syntheses reinforces the influence of subtle matching and/or mismatching interactions on the outcome of convergent oligosaccharide synthesis.

Synthesis of glycoconjugate vaccines for Candida albicans using novel linker methodology

[reaction: see text] The cell wall phosphomannan of Candida species is a complex N-linked glycoprotein with a glycan chain that contains predominantly alpha-linked mannose residues. However, it is the minor beta-mannan component of the phosphomannan of clinically important Candida strains that provides immunological protection in animal models of fungal disease and hence holds promise as a component of conjugate vaccines. This important antigen occurs in different forms linked to the alpha-mannan backbone via a phosphodiester bond (acid-labile beta-mannan) or directly via a glycosidic bond. To reproducibly synthesize and evaluate conjugate vaccines, a robust method for the synthesis of the different oligosaccharide epitopes is required. Here, we report the gram-scale syntheses of both types of epitopes by an approach that utilizes glucosyl trichloroacetimidate donor 2 to first create a beta-glucopyranoside linkage and then epimerizes the C-2 center via an oxidation-reduction sequence that provides an efficient multigram scale route to the beta-mannopyranosides 5, 8, and 15. Reaction of glycosides 16-18 with homobifunctional adipic acid p-nitrophenyl diesters in dry DMF gave the corresponding half esters in good yields, and of sufficient stability to permit chromatographic purification. Subsequent conjugation with BSA and tetanus toxiod (TT) under mild conjugation conditions afforded the corresponding tri- and tetrasaccharide neoglycoproteins with good efficiency. The conjugation method is also applicable to the coupling of small amounts (mg) of larger oligosaccharides with different proteins.

Toward synthesis of the regular sequence of heparin: synthesis of two tetrasaccharide precursors

Two fully protected tetrasaccharides, which represent precursors for the synthesis of the regular sequence of heparin, were synthesized via coupling of a pair of disaccharide trichloroacetimidates with a thioglycoside and a glucosamine derivative, respectively, in a sequential manner.

A new homobifunctional p-nitro phenyl ester coupling reagent for the preparation of neoglycoproteins

A new linker system has been designed and applied to neoglycoprotein synthesis. Reaction of oligosaccharide omega-aminoalkyl glycosides with homobifunctional adipic acid p-nitrophenyl diesters in dry DMF gave the corresponding amide half ester in good yields and of sufficient stability to permit chromatographic purification. Subsequent conjugation with bovine serum albumin under very mild conditions afforded the corresponding neoglycoproteins with good efficiency. The method is well suited for the coupling of very small amounts (mg) of oligosaccharide and protein. [structure: see text]