Search

6-O-Acetylated derivatives of D-hexopyranosides are valuable intermediates in synthetic carbohydrate chemistry. We have developed a new simple procedure for selective acetylation of the primary hydroxyl group in methyl D-hexopyranosides consisting in treatment with a mixture of acetic anhydride and acetic acid at 50°C. As a result, corresponding 6-acetates were formed in 40–50% yield.

High-resolution electrospray mass spectra (MS and MS/MS CID) of positive ions of a series of protonated, ammoniated, and metallated molecules of cyclic N-substituted oligo-&beta, (1&rarr, 6)-D-glucosamines differing in cycle size and N-acyl substituents were registered and interpreted. It was shown that the main type of fragmentation is a cleavage of glycosidic bonds of a cycle, and in some cases fragmentation of amide side chains is possible. If labile fragments in substituents (e.g., carbohydrate chains) are present, a decay of the cycle and an elimination of labile fragments are of comparable possibility. It was found that in some cases rearrangements with loss of an internal carbohydrate residue (IRL), or an internal part of a side chain, are feasible.

A linear tetramer of β-(1 → 6)-linked 3-azido-3-deoxy- d -allose containing glycosyl donor and glycosyl acceptor functions in the terminal monosaccharide units was prepared starting from 3-azido-3-deoxy-1,2:5,6-di-O-isopropylidene-α- d -allofuranose. Cyclization of the linear tetramer under glycosylation conditions afforded the corresponding cyclic tetrasaccharide in 77% yield; its deprotection and reduction of the azido groups resulted in the formation of the cyclic tetramer of 3-amino-3-deoxy- d -allose with axial amino groups, a potential scaffold for the synthesis of tetravalent functional clusters.

2-Aminoethyl glycoside of the pseudotetrasaccharide α-d-Glcp-(1→3)-α-l-Rhap-(1→4)-d-Rib-ol-(5-P-2)-α-d-Galp structurally related to a repeating unit of the Streptococcus pneumoniae type 6B capsular...

Two glucosyl donors, which allowed for the α-selective glucosylation of primary hydroxyl groups, were designed using a combination of acyl groups capable of remote participation, an electron-withdrawing pentafluorobenzoyl substituent and a bulky TBDPS protecting group. The first had a participating levulinoyl group at O-3 and the TBDPS protecting group at O-6, and the second bore an acetyl group at O-3 and the pentafluorobenzoyl one at O-6. With the help of these donors, two synthetic schemes, convergent and linear, towards a pentaglucoside representing the α-(1→6)-linked glucans of Helicobacter pylori were evaluated. The linear scheme proved to be preferential over the convergent one because of its insufficiently high α-stereoselectivity demonstrated by disaccharide donors. For the linear scheme, the pentafluorobenzoyl group turned out to be more convenient than TBDPS at the removal step. The α-(1→6)-linked pentaglucoside was prepared by iteration of glucosylation with the donor bearing 3-O-acetyl and 6-O-pentafluorobenzoyl and the subsequent liberation of the 6-OH group. Biotin was attached to the pentaglucoside via the spacer amino group.

The carbohydrate specificity of antibodies obtained by immunizing laboratory animals with immunogens prepared from the Aspergillus fumigatus cell wall was analyzed using the library of biotinylated synthetic oligosaccharides. It has been shown that the main part of antipolysaccharide antibodies recognizes galactomannan in the studied immunogens with preference to its fragments containing more than two β-(1→5)-linked galactofuranosyl units. The data obtained can form the basis for the development of enzyme immunoassay for the detection of this dangerous fungal pathogen.

International audience; Biotinylated hepta-, nona- and undeca-α-(1 → 3)-d-glucosides representing long oligosaccharides of α-(1 → 3)-d-glucan, one of the major components of the cell walls of the fungal pathogen Aspergillus fumigatus, were synthesized for the first time via a blockwise strategy. Convergent assembly of the α-(1 → 3)-d-glucan chains was achieved by glycosylation with oligoglucoside derivatives bearing 6- O-benzoyl groups. Those groups are capable of remote α-stereocontrolling participation, making them efficient α-directing tools even in the case of large glycosyl donors. Synthetic biotinylated oligoglucosides (and biotinylated derivatives of previously synthesized tri- and penta-α-(1 → 3)-d-glucosides) loaded on streptavidin microtiter plates were shown to be better recognized by anti-α-(1 → 3)-glucan human polyclonal antibodies and to induce higher cytokine responses upon stimulation of human peripheral blood mononuclear cells than their natural counterpart, α-(1 → 3)-d-glucan, immobilized on a conventional microtiter plate. Attachment of the synthetic oligosaccharides equipped with a hydrophilic spacer via the streptavidin-biotin pair allows better spatial presentation and control of the loading compared to the random sorption of natural α-(1 → 3)-glucan. Increase of oligoglucoside length results in their better recognition and enhancement of cytokine production. Thus, using synthetic α-(1 → 3)-glucan oligosaccharides, we developed an assay for the host immune response that is more sensitive than the assay based on native α-(1 → 3)-glucan.

The disaccharide β-d-mannopyranosyl-(1 → 2)-d-mannopyranose obtained by chemical cleavage and enzymatic dephosphorylation of biotechnologically available phosphomannan was transformed over six steps into a biotinylated probe suitable for assessment of carbohydrate specificity of antibodies induced by yeast cell wall preparations.

Efficient glycosylation with phenyl 2-azido-2-deoxy-1-seleno-α- d -galactosides of glycosyl acceptors with different reactivities has been developed. The reaction provided glycosides of 2-azido-2-deoxy- d -galactose in good to high yields. The stereochemical outcome of the glycosylation of reactive acceptors (3-trifluoroacetamidopropanol and methyl 2,3- O -isopropylidene-α- l -rhamnopyranoside) can be broadly varied from complete β- to high α-selectivity by changing the reaction solvent, promoter and protecting groups in the donor, while the glycosylation of less reactive allyl 2,2′,3,3′,6,6′-hexa- O -benzoyl-β-lactoside afforded the corresponding α-glycosides exclusively.

Oligomannosides comprising short β-(1→2)-oligomannosyl blocks attached through a glycoside bond to an α-(1→2)-linked oligomannoside are a constituent of side chains of the mannan from the Candida cell wall. This type of oligomannoside is known as an acid-stable β-mannan and corresponds to the antigenic factor 6. In this communication, we report a convergent blockwise synthesis of four spacer-armed oligomannosides of this type including from 1 to 4 β-mannosyl and 2–3 α-mannosyl residues. β-(1→2)-Oligomannosyl thioglycosides and sulfoxides containing up to four mannose units were employed for introduction of β-oligomannoside sequences. The efficiency of β-mannosylation with mono- and oligomannoside donors was shown to depend more on the structure of the reaction partners than on the applied activation protocol. The oligomannosides obtained will be used to prepare various molecular tools for investigation of the Candida cell wall.

Oligosaccharides have a variety of versatile biological effects, but unlike peptides and oligonucleotides, investigation of the roles of oligosaccharides is not easy. Since biosynthesis of oligosaccharides does not comply with direct genetic control, their isolation from natural sources and biotechnological preparation are complicated, due to the heterogeneous composition of raw carbohydrates. Oligosaccharide synthesis is needed for the establishment or confirmation of the structure of natural glycocompounds. Also, synthetically prepared, defined oligosaccharides and their derivatives are becoming increasingly important tools for many biological and immunological research projects. The key step of oligosaccharide synthesis involves glycosylation, a reaction that builds glycosidic bonds. Usually, construction of 1,2-trans-bonds is easy, and therefore, this reaction can even be included into automated syntheses. At this time, installation of the 1,2-cis-bond remains simultaneously frustrating and compelling. In our and other laboratories, a strategy of α-selective (1,2-cis) glycosylation, relying on remote anchimeric assistance with acyl groups, is studied. The state of the art in this work is summarized in this review.

3-Aminopropyl glycosides of a series of linear β-(1 → 3)-linked D-glucooligosaccharides containing from 3 to 13 monosaccharide units were efficiently prepared. The synthetic scheme featured highly regioselective glycosylation of 4,6-O-benzylidene-protected 2,3-diol glycosyl acceptors with a disaccharide thioglycoside donor bearing chloroacetyl groups at O-2' and -3' as a temporary protection of the diol system. Iteration of the deprotection and glycosylation steps afforded the series of the title oligoglucosides differing in length by two monosaccharide units. A novel procedure for selective removal of acetyl groups in the presence of benzoyl ones consisting in a brief treatment with a large excess of hydrazine hydrate has been proposed.

3-Aminopropyl β-(1 → 6)- d -glucotetraoside has been synthesized from 3-benzyloxycarbonylaminopropanol and 6- O -acetyl-2,3,4-tri- O -benzoyl- d -glucopyranosyl trichloroacetimidate by successive attachment of one monosaccharide unit in total yield of 22%. Free aminopropyl glycoside was converted into a biotin derivative that can be used for controlled immobilization of the oligosaccharide on streptavidin-coated ELISA plates and for tracing carbohydrate binding molecules.

The strength of 1,3-syn-diaxial repulsion was evaluated for main types of protecting groups (alkyl, silyl, and acyl) usually used in carbohydrate chemistry. As molecular probes for this study, derivatives of isopropyl 2-O-benzyl-4,6-O-benzylidene-α-d-idopyranoside bearing allyl, acetyl, and tert-butyldiphenylsilyl (TBDPS) protecting groups at O-3 were prepared from p-methoxyphenyl d-galactopyranoside. The equilibrium between OS2 and 4C1 conformations in these compounds was investigated using 3JH,H and 3JC,H coupling constants that were determined from 1D 1H NMR and 2D J-resolved HMBC spectra in various solvents. The analysis of the corresponding coupling constants calculated using DFT/B3LYP/pcJ-1 approximation applied to conformations optimized at DFT/B3LYP/6-311++G** level supported the investigation. Proportions of conformers in the equilibrium revealed the highest repulsion between the 3-allyloxy group and the isopropoxy aglycon and its dependence on the solvent polarity. Differences in the conformatio...

A family of fifteen glycoclusters based on a cyclic oligo-(1→6)-β-D-glucosamine core has been designed as potential inhibitors of the bacterial lectin LecA with various valencies (from 2 to 4) and linkers. Evaluation of their binding properties towards LecA has been performed by a combination of hemagglutination inhibition assays (HIA), enzyme-linked lectin assays (ELLA), and isothermal titration microcalorimetry (ITC). Divalent ligands displayed dissociation constants in the sub-micromolar range and tetravalent ligands displayed low nanomolar affinities for this lectin. The influence of the linker could also be demonstrated; aromatic moieties are the best scaffolds for binding to the lectin. The affinities observed in vitro were then correlated with molecular models to rationalize the possible binding modes of these glycoclusters with the bacterial lectin.

The conformational behavior of linear oligo-β-(1→3)-D-glucosides was studied using NMR experiments and molecular modeling. The explicit solvent model in calculations yielded the best coincidence between experimental and theoretical values of NOE and spin-spin coupling constants to evidence the strong influence of solvation upon the conformations of the oligoglucosides. Long-range coupling constants calculated for di- and trimeric clusters of the studied glucosides fit the experimental data much better than the single-molecule approach. It was shown that conformational properties of disaccharide fragments in studied oligoglucosides depended on neither their position in the chain nor the length of the chain.

The synthesis was described of branched glucooctaoside bearing the β-(1 → 3)-glucotrioside side chain at O-6 of the second (from the reducing end) monosaccharide unit of the linear β-(1 → 3)-glucopentaoside core.

Cystic fibrosis (CF) is a congenital disease caused by a mutation in a gene responsible for the synthesis of a membrane protein called the cystic fibrosis transmembrane conductance regulator (CFTR). Resistance to Pseudomonas aeruginosa infection is closely related to the biological properties of CFTR; however, these properties have not been clearly linked to the known role of CFTR as a chloride and bicarbonate ion channel. Indeed, data indicate that CFTR is an epithelial cell receptor for P. aeruginosa, with CFTR binding to the oligosaccharide of the outer core region of the bacterial lipopolysaccharide (LPS), of which two distinct glycoforms have been identified. Binding leads to effective innate immunity to clear this pathogen in individuals with wild-type CFTR. To reveal the molecular basis of elimination of the bacterium through this interaction, the synthesis of pentasaccharides corresponding to both glycoforms of the outer core region of P. aeruginosa LPS was undertaken. Here we report the synthesis of the glycoform II. Like glycoform I, it was prepared as three pentasaccharides bearing naturally occurring N-alanyl and N-acetyl substituents in the galactosamine moiety as well as unnatural N-acetylalanine to reveal the role of the amino group in the alanyl substituent. Key features of the synthesis were two α-glucosylations with glucosyl donors bearing α-stereodirecting acyl groups at O-6 and/or O-3 and high-yielding reduction of the azido group followed by N-acylation and final O-debenzylation.

The first synthesis of a series of homologous cyclic oligo-(1→6)-β-D-glucosamines consisting of two to seven residues and representing a new type of functionalized cyclic oligosaccharides is reported. Remarkably high yields of the studied macrocyclization reaction irrespective of the length of the acyclic precursors were observed. In the case of compounds constituted of four to seven glucosamine units α-stereoisomers formed as side products despite the presence of a strongly participating 2-N-phthaloyl group to control β-glycosylation. Both phenomena may be accounted for by conformational features of the linear bifunctional precursors. According to computer modeling and NMR conformational studies, the described linear (1→6)-β-linked oligoglucosamines exist in a right-handed helix-like conformation, in which the glycosyl donor and acceptor moieties are prearranged in a way that facilitates intramolecular glycosylation from the α-side. Prepared cyclo-oligoglucosamines differ in their conformational flexibilities, as illustrated by their spectral characteristics and calculated asphericity distributions. Moreover, the obtained compounds do not possess a distinct hydrophobic cavity, which is in contrast to the well-known cyclodextrins. All these characteristics provide an excellent basis for the use of these novel cyclic oligosaccharides as scaffolds for the construction of biomolecular conjugates.

The first synthesis of the common trisaccharide of glycoforms of the outer core region of the Pseudomonas aeruginosa lipopolysaccharide is reported. A fully protected trisaccharide precursor was prepared via a highly efficient α-(1→4)-glucosylation of a β-(1→3)-linked 6-O-benzyl-2-azido-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl-β- d -glucopyranosyl)-α- d -galactopyranoside. In contrast, an alternative sequence of glycosylations, which involves β-glucosylation of an α-(1→4)-linked Glc-GalN3 unit, did not lead to the target trisaccharide backbone. Further O-deacetylation, azido group reduction and debenzylation of the protected trisaccharide precursor gave the corresponding trisaccharide amine. The latter structure was used in the synthesis of a series of trisaccharides bearing an acetyl group, an l -alanine or an N-acetylated l -alanine residue on its amino group at C-2 of GalN.

The phosphorylated branched heptasaccharides 7 and 8, the octasaccharide 9 and the phosphorylated trisaccharides 5 and 6, which are fragments of the phosphoglycan portion of the surface lipophosphoglycans from Leishmania mexicana (5) or L. major (6-9), were synthesised by using the glycosyl hydrogenphosphonate method for the preparation of phosphodiester bridges. The compounds were tested as acceptor substrates/putative inhibitors for the Leishmania elongating alpha-D-mannosylphosphate transferase.

It has been shown that O-chloroacetyl protecting groups enhance significantly sialylating activity of 2-thioethyl sialosides in model reactions of α(2-8)-sialylation. Ethyl 4,7,8,9-tetra-O-chloroacetyl-3,5-dideoxy-2-thio-5-trifluoroacetamido-D-glycero-α-D-galacto-non-2-ulopyranoside that combines electron-withdrawing O-chloroacetyl and N-trifluoroacetyl protecting groups displayed the best reactivity and enabled the most efficient synthesis of the Neu5Aca(2-8)Neu5Ac dimer. The GD 3 tetrasaccharide was synthesized in stepwise manner using this sialyl donor in the key (2-8)-coupling, albeit the yield was noticeably lower than in the model sialylation of monosaccharide acceptors.

International audience; 3-Aminopropyl α-(1→3)-pentaglucoside, a fragment of α-(1→3)-glucan of the cell wall of Aspergillus fumigatus, has been synthesized in a blockwise approach. The application of mono- and disaccharide N-phenyltrifluoroacetimidates bearing a stereodirecting 6-O-benzoyl group was essential for stereoselective α-glucosylations. In the products, p-methoxyphenyl and levulinoyl groups served as orthogonal protecting groups for the anomeric position and 3-OH group, respectively. Their removal from shared blocks led to donors and acceptors that were used for the synthesis of pentasaccharides. Coupling of free α-(1→3)-pentaglucoside with biotin and bovine serum albumin (BSA) gave glycoconjugate tools for mycological studies. Immunization of mice with the BSA conjugate induced the generation of antibodies that recognize α-(1→3)-glucan on A. fumigatus cell wall and distinguish its morphotypes. This discovery represents a first step to the development of a diagnostic test system and a vaccine to detect and fight this life-threatening pathogen.

5,7-Diacetamido-3,5,7,9-tetradeoxy-D-glycero-D-galacto- and -D-glycero-D-talo-non-2-ulosonic acids were synthesized by condensation of 2,4-diacetamido-2,4,6-trideoxy-D-mannose with oxalacetic acid. Comparison of the 1H and 13C NMR data and the specific optical rotation values of these monosaccharides and the corresponding L-glycero-D-galacto and L-glycero-D-talo isomers synthesized earlier [Tsvetkov, Y. E.; Shashkov, A. S.; Knirel, Y. A.; Backinowsky, L. V.; Zähringer, U. Mendeleev Commun. 2000, 90-92] with data of the natural compounds enabled the identification in bacterial lipopolysaccharides of derivatives of 5,7-diamino-3,5,7,9-tetradeoxy-D-glycero-D-galacto-non-2-ulosonic (legionaminic) acid and epimers of legionaminic acid at C-4 and C-8.

Two mimetics of dec-9-enyl β- d -galactopyranosyl-(1→4)-α- d -mannopyranosyl phosphate containing the phosphodiester ( 3 ) or phosphonate ( 4 ) groups have been synthesized.

The triglycosyl monophosphate 1 , heptaglycosyl triphosphates 2 and 3 , and octaglycosyl triphosphate 4 , which are fragments of the phosphoglycan part of Leishmania major lipo- and proteo-phosphoglycans have been prepared using di- and tri-saccharide H-phosphonates for construction of the phosphodiester bridges.

The effect of a 3-O-acetyl group on the stereoselectivity of α-glycosylation with 2-O-benzylated D-gluco glycosyl donors was studied. It was shown that 3-O-acetylated donors gave α-anomers predominantly or exclusively, whereas glycosylation with the corresponding per-O-benzylated donors afforded mixtures of comparable amounts of α- and β-anomers. The higher α-stereoselectivity in the first case was accounted for by the remote anchimeric assistance of the 3-O-acetyl group, which was confirmed by theoretical calculations.

2-O-Unprotected and 2-deoxy-2,3-dehydro-neuraminic acid derivatives 2, 4, and 10 exhibit enhanced acceptor properties at their 8-hydroxy group in sialylation reactions with phosphite 5 as donor; yet, mainly (10) or exclusively (2, 4) β-glycoside bond formation was observed. The 3-phenylthionocarbonate group as stereodirecting auxiliary group in the sialyl donor 11 led with 10 as acceptor to exclusive formation of α(2–8)-linked disaccharide.

The stereodirecting effect of a 3- O -acetyl protecting group, which is potentially capable of the remote anchimeric participation, and other protecting groups in 2- O -benzyl glucosyl donors with flexible and rigid conformations has been investigated. To this aim, an array of N -phenyltrifluoroacetimidoyl and sulfoxide donors bearing either 3- O -acetyl or 3- O -benzyl groups in combination with 4,6-di- O -benzyl, 6- O -acyl-4- O -benzyl, or 4,6- O -benzylidene protecting groups was prepared. The conformationally flexible 3-O-acetylated glucosyl donor protected at other positions with O -benzyl groups demonstrated very low or no α-stereoselectivity upon glycosylation of primary or secondary acceptors. On the contrary, 3,6-di-O-acylated glucosyl donors proved to be highly α-stereoselective as well as the donor having a single potentially participating acetyl group at O-6. The 3,6-di-O-acylated donor was shown to be the best α-glucosylating block for the primary acceptor, whereas the best α-selectivity of glycosylation of the secondary acceptor was achieved with the 6-O-acylated donor. Glycosylation of the secondary acceptor with the conformationally constrained 3- O -acetyl-4,6- O -benzylidene-protected donor displayed under standard conditions (−35 °C) even lower α-selectivity as compared to the 3- O -benzyl analogue. However, increasing the reaction temperature essentially raised the α-stereoselectivities of glycosylation with both 3- O -acetyl and 3- O -benzyl donors and made them almost equal. The stereodirecting effects of protecting groups observed for N -phenyltrifluoroacetimidoyl donors were also generally proven for sulfoxide donors.

The glycosylation of sugar primary-secondary ditrityl ethers with glycosylating agents of different kinds occurs regioselectively at the secondary trityloxy group to give good yields of 6-O-trityl ethers of 1-2-, 1-3-, and 1-4-linked disaccharides. For a preliminary communication see Yu. E. Tsvetkov. P. I. Kitov, L. V. Backinowsky. and N. K. Kochetkov. Tetrahedron Lett. 34. 7977 (1 993).

Synthesis of two isomeric tetrasaccharides, namely Neu5Acα(2→3)Galβ(1→3)[Fucα(1→4)GlcNAcβ (sLea) and Neu5Acα(2→3)Galβ(1→4)[Fucα(1→3)]GlcNAcβ (sLex) as 3-aminopropyl glycosides is described. Preparation of these compounds was performed by sialylation of selectively protected trisaccharides Lea and Lex which contain three unsubstituted OH groups at positions 2, 3 and 4 of Gal residue. Glycosylation of Lex trisaccharide with ethylthio sialoside under promotion by NIS and TfOH in acetonitrile was effective and regio- and stereoselective to give sLex derivative in 81% yield. In contrast, sialylation of the Lca acceptor was accompanied by a variety of undesirable by-processes, namely. N-thioethylation of the GlcNAc residue, β-sialylation, and lactonisation. In order to improve the yield of sLca tetrasaccharide the glycosylation of Lea acceptor by sialyl donors of ethyl and phenyl thioglycoside (promoted by NIS-TfOH or NBS-Bu4NBr), xanthate (promotion by NIS-TfOH mixture or MeOTf) and phosphite (promote...

Reaction of 8-O-unprotected Neu5Ac-1,7-lactone derivatives 3a–c, which were readily obtained from Neu5Ac, gave with sialyl donor 4 exclusively β(2–8)-linked disaccharides 5a–c in good yields. The lactone ring in disaccharides 5a–c was readily cleaved, thus 5c afforded Neu5Acβ(2–8)Neu5Ac derivative 6.

The conformational behavior of a series of linear and cyclic oligo-(1→6)-β- d -glucosamines and their N-acetylated derivatives, which are related to fragments of natural poly- N -acetylglucosamine, was studied by theoretical molecular modeling and experimental determination of transglycosidic vicinal coupling constants 3 J C,H and 3 J H,H . Molecular dynamics simulations were performed under several types of conditions varying in the consideration of ionization of amino groups, solvent effect, and temperature. Neural network clustering and asphericity calculations were performed on the basis of molecular dynamics data. It was shown that disaccharide fragments in the studied linear oligosaccharides were not rigid, and tended to have several conformers, thus determining the overall twisted shape with helical elements. In addition, it was found that the behavior of C5–C6 bond depended significantly upon the simulation conditions. The cyclic di-, tri-, and tetrasaccharides mostly had symmetrical ring-shaped conformations. The larger cycles tended to adopt more complicated shapes, and the conformational behavior of their disaccharide fragments was close to that in the linear oligosaccharides.

A series of five 3-acetamidopropyl β-glycosides of nona-β-(1→6)-glucosamines containing two N-acetylglucosamine residues separated by a different number of glucosamine units with free amino groups have been synthesized using a convergent blockwise approach. Oxazoline glycosylation was used to introduce N-acetylglucosamine residues. These nonasaccharides are structurally related to the poly-N-acetylglucosamine (PNAG) extracellular polysaccharide of Staphylococcus aureus and can be used as models for biochemical and immunological studies.

Primary-secondary sugar ditrityl ethers are selectively glycosylated at the secondary position

Base-promoted reaction of tetra-O-benzyl-glucose 1a with secondary alkyl trifluoromethanesulfonates 2 and 3 in toluene provides in the presence of 15-crown-5 preferentially β-glycosides 2aβ and 3aβ, respectively, in high yields. For reactions carried out at lower temperatures and with trifluoromethanesulfonates derived from secondary hydroxy groups of sugars aprotic dipolar solvents (HMPT/DMF, HMPT/THF) are required. Thus, treatment of 1-O-unprotected hexoses 1a–e with trifluoromethanesulfonates 4, 6, and 7 affords the corresponding (14)-connected disaccharides 4a–e and the (13)-connected disaccharides 6b and 7b, respectively, in high yields. Under these conditions the α:β ratio of the products resembled the anomeric ratio of the starting material.

Uridine 5′-diphosphate α-D-galactofuranose, which is likely to be a biochemical donor of D-galactofuranosyl residues in Nature, is synthesized from α-D-galactofuranosyl phosphate and uridine 5′-monophosphate.

The synthesis of a pentasaccharide representing the glycoform I, which is one of two naturally occurring glycoforms of the outer core of Pseudomonas aeruginosa lipopolysaccharide, and its analogues, differing in the N-substituent in the galactosamine unit, is reported. The main features of the synthetic scheme included the assembly of the pentasaccharide backbone by successive introduction of monosaccharide units, the use of glucosyl donors with specific location of acyl protecting groups capable of the remote anchimeric participation for highly stereoselective alpha-glucosylation, and efficient reduction of the azido group allowing high-yielding transformation of the intermediary azido pentasaccharide into final products.

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.

A series of 3-beta-acetamidopropyl oligo-beta-(1-->6)-glucosamines consisting of 5, 7, 9 and 11 glucosamine residues, and a series of corresponding per-N-acetylated derivatives were synthesized using a convergent blockwise approach. These compounds represent fragments of a bacterial surface polysaccharide produced by numerous bacterial pathogens, including Staphylococcus aureus, and will be used as models for its biochemical and immunological properties.

Derivatives of 5,7-diamino-3,5,7,9-tetradeoxynon-2-ulosonic acids are essential constituents of some bacterial polysaccharides and glycoproteins. In order to establish reliably the configuration of the natural sugars, nine stereoisomeric 5,7-diacetamido-3,5,7,9-tetradeoxynon-2-ulosonic acids were synthesized, including di- N -acetyl-legionaminic and -pseudaminic acids (the d -glycero- d -galacto and l -glycero- l -manno isomers, respectively) and their isomers at C-4, C-5, C-7, and C-8 having the l -glycero- d -galacto, d -glycero- d -talo, l -glycero- d -talo, d -glycero- l -altro, l -glycero- l -altro, d -glycero- l -manno, and l -glycero- l -gluco configurations. Synthesis was performed by condensation of 2,4-diacetamido-2,4,6-trideoxy- l -gulose, - d -mannose, - d -talose, and - l -allose with oxalacetic acid under basic conditions, the reaction of the last two precursors being accompanied by epimerisation at C-2. The 1 H and 13 C NMR data of the synthetic compounds are discussed. Acetylated methyl esters of the C-7 and C-8 isomeric nonulosonic acids were prepared and used for analysis of the side-chain conformation by NMR spectroscopy.