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This study describes a new convenient method for the photocatalytic generation of glycosyl fluorides using sulfur(VI) hexafluoride as an inexpensive and safe fluorinating agent and 4,4′-dimethoxybenzophenone as a readily available organic photocatalyst. This mild method was employed to generate 16 different glycosyl fluorides, including the substrates with acid and base labile functionalities, in yields of 43%-97%, and it was applied in continuous flow to accomplish fluorination on an 7.7 g scale and 93% yield.

L-Hexoses are rare but biologically significant components of various important biomolecules. However, most are prohibitively expensive (if commercially available) which limits their study and biotechnological exploitation. New, efficient methods to access L-hexoses and their derivatives are thus of great interest. In a previous study, we showcased a stereoselective Bu3SnH-mediated transformation of a 5-C-bromo-D-glucuronide to an L-iduronide. We have now drawn inspiration from this result to derive a new methodology – one that can be harnessed to access other L-hexoses. DFT calculations demonstrate that a combination of a β-F at the anomeric position and a methoxycarbonyl substituent at C-6 is key to optimising the selectivity for the L-hexose product. Our investigations have also culminated in the development of the shortest known synthetic route to a derivative of L-idose from a commercially available starting material (45 % yield over 3 steps). Collectively, these results address the profound lack of understanding of how to synthesise L-hexoses in a stereoselective fashion.

The Thomsen-Friedenreich-antigen, Gal(β1–3)GalNAc(α1-O-Ser/Thr (TF-antigen), is presented on the surface of most human cancer cell types. Its interaction with galectin 1 and galectin 3 leads to tumor cell aggregation and promotes cancer metastasis and T-cell apoptosis in epithelial tissue. To further explore multivalent binding between the TF-antigen and galectin-3, the TF-antigen was enzymatically synthesized in high yields with GalNAc(α1-EG3-azide as the acceptor substrate by use of the glycosynthase BgaC/Glu233Gly. Subsequently, it was coupled to alkynyl-functionalized bovine serum albumin via a copper(I)-catalyzed alkyne-azide cycloaddition. This procedure yielded neo-glycoproteins with tunable glycan multivalency for binding studies. Glycan densities between 2 and 53 glycan residues per protein molecule were obtained by regulated alkynyl-modification of the lysine residues of BSA. The number of coupled glycans was quantified by sodium dodecyl sulfate polyacrylamide gel electrophoresis and a trinitrobenzene sulfonic acid assay. The binding efficiency of the neo-glycoproteins with human galectin-3 and the effect of multivalency was investigated and assessed using an enzyme-linked lectin assay. Immobilized neo-glycoproteins of all modification densities showed binding of Gal-3 with increasing glycan density. However, multivalent glycan presentation did not result in a higher binding affinity. In contrast, inhibition of Gal-3 binding to asialofetuin was effective. The relative inhibitory potency was increased by a factor of 142 for neo-glycoproteins displaying 10 glycans/protein in contrast to highly decorated inhibitors with only 2-fold increase. In summary, the functionality of BSA-based neo-glycoproteins presenting the TF-antigen as multivalent inhibitors for Gal-3 was demonstrated.

The chemical synthesis of pyridoxine-5′-β-D-glucoside (5′-β-PNG) was investigated using various glucoside donors and promoters. Hereby, the combination of α4,3-O-isopropylidene pyridoxine, glucose vested with different leaving and protecting groups and the application of stoichiometric amounts of different promoters was examined with regards to the preparation of the twofold protected PNG. Best results were obtained with 2,3,4,6-tetra-O-acetyl-D-glucopyranosyl fluoride and boron trifluoride etherate (2.0 eq.) as promoter at 0 °C (59%). The deprotection was accomplished stepwise with potassium/sodium hydroxide in acetonitrile/water followed by acid hydrolysis with formic acid resulting in the chemical synthesis of 5′-β-PNG.

We disclose a novel radical strategy for the fluorination of alkyl bromides via the merger of silyl radical-mediated halogen-atom abstraction and benzophenone photosensitization. Selectivity for halogen-atom abstraction from alkyl bromides is observed in the presence of an electrophilic fluorinating reagent containing a weak N-F bond despite the predicted favorability for Si-F bond formation. To probe this surprising selectivity, preliminary mechanistic and computational studies were conducted, revealing that a radical chain mechanism is operative in which kinetic selectivity for Si-Br abstraction dominates due to a combination of polar effects and halogen-atom polarizability in the transition state. This transition-metal-free fluorination protocol tolerates a broad range of functional groups, including alcohols, ketones, and aldehydes, which demonstrates the complementary nature of this strategy to existing fluorination technologies. This system has been extended to the generation of gem-difluorinated motifs which are commonly found in medicinal agents and agrochemicals.

The invention provides a chemical synthetic method for beta-arbutin, which includes: 1) performing a reaction to pentaacetyl-beta-D-glucose with a 70% hydrofluoric acid pyridine solution at 10-30 DEGC to obtain tetraacetyl-alpha-fluoroglucose; 2) performing a reaction to the tetraacetyl-alpha-fluoroglucose with p-hydroxyacetophenone in a mixed solvent under catalysis of tetrabutylammonium bromidewith Ca(OH)2 being an accelerant at 20-30 DEG C to prepare p-acetylphenyl-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside; 3) performing a reaction to the p-acetylphenyl-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside with 40% peroxyacetic acid in an organic solvent at 5-20 DEG C to obtain p-acetoxylphenyl-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside; 4) performing a reaction to the p-acetoxylphenyl-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside at 15-25 DEG C in the presence of anhydrous methanol-sodium methoxide to obtain the beta-arbutin. The method is high in yield, low in cost, gentle in conditions and less in emission of waste liquid, waste gas and waste solids, and is suitable for industrial production.

Photocatalytic formation of glycosidic bonds employing stable and readily accessible O-glycosyl derivatives of 2,2,6,6-tetramethylpiperidin-1-ol is presented that employs an iridium-based photocatalyst and blue LEDs. The reaction proceeds at room temperature and in the absence of additives other than 4 ? molecular sieves. Stereoselectivities are modest but nevertheless dependent on the anomeric configuration of the donor, suggesting a substantial degree of concerted character.

An object of the present invention is to provide a novel substance that has a high reactivity as a fluorinating agent, is effectively used in various fluorination reactions, and is safely handled even in air. As the solution for achieving this object, the present invention provides a complex obtained by reacting bromine trifluoride with at least one metal halide selected from the group consisting of halogenated metals and halogenated hydrogen metals in a nonpolar solvent. This complex serves as a fluorinating agent that provides excellent fluorination performance and that is stable in air.

An effective method for the chemical synthesis of cyanogenic glucosides has been developed as demonstrated by the synthesis of dhurrin, taxiphyllin, prunasin, sambunigrin, heterodendrin, and epiheterodendrin. O-Trimethylsilylated cyanohydrins were prepared and subjected directly to glucosylation using a fully acetylated glucopyranosyl fluoride donor with boron trifluoride-diethyl etherate as promoter to afford a chromatographically separable epimeric mixture of the corresponding acetylated cyanogenic glucosides. The isolated epimers were deprotected using a triflic acid/MeOH/ion-exchange resin system without any epimerization of the cyanohydrin function. The method is stereocontrolled and provides an efficient approach to chemical synthesis of other naturally occurring cyanogenic glucosides including those with a more complex aglycone structure.

We report a synthetic glycosylation reaction between sucrosyl acceptors and glycosyl fluoride donors to yield the derived trisaccharides. This reaction proceeds at room temperature in an aqueous solvent mixture. Calcium salts and a tertiary amine base promote the reaction with high site-selectivity for either the 3′-position or 1′-position of the fructofuranoside unit. Because nonenzymatic aqueous oligosaccharide syntheses are underdeveloped, mechanistic studies were carried out in order to identify the origin of the selectivity, which we hypothesized was related to the structure of the hydroxyl group array in sucrose. The solution conformation of various monodeoxysucrose analogs revealed the co-operative nature of the hydroxyl groups in mediating both this aqueous glycosyl bond-forming reaction and the site-selectivity at the same time.

Streptomyces coelicolor (Sco) GlgEI is a glycoside hydrolase involved in α-glucan biosynthesis and can be used as a model enzyme for structure-based inhibitor design targeting Mycobacterium tuberculosis (Mtb) GlgE. The latter is a genetically validated drug target for the development of anti-Tuberculosis (TB) treatments. Inhibition of Mtb GlgE results in a lethal buildup of the GlgE substrate maltose-1-phosphate (M1P). However, Mtb GlgE is difficult to crystallize and affords lower resolution X-ray structures. Sco GlgEI-V279S on the other hand crystallizes readily, produces high resolution X-ray data, and has active site topology identical to Mtb GlgE. We report the X-ray structure of Sco GlgEI-V279S in complex with 2-deoxy-2,2-difluoro-α-maltosyl fluoride (α-MTF, 5) at 2.3 ? resolution. α-MTF was designed as a non-hydrolysable mimic of M1P to probe the active site of GlgE1 prior to covalent bond formation without disruption of catalytic residues. The α-MTF complex revealed hydrogen bonding between Glu423 and the C1F which provides evidence that Glu423 functions as proton donor during catalysis. Further, hydrogen bonding between Arg392 and the axial C2 difluoromethylene moiety of α-MTF was observed suggesting that the C2 position tolerates substitution with hydrogen bond acceptors. The key step in the synthesis of α-MDF was transformation of peracetylated 2-fluoro-maltal 1 into peracetylated 2,2-difluoro-α-maltosyl fluoride 2 in a single step via the use of Selectfluor.

Streptomyces coelicolor (Sco) GlgEI is a glycoside hydrolase involved in α-glucan biosynthesis and can be used as a model enzyme for structure-based inhibitor design targeting Mycobacterium tuberculosis (Mtb) GlgE. The latter is a genetically validated drug target for the development of anti-Tuberculosis (TB) treatments. Inhibition of Mtb GlgE results in a lethal buildup of the GlgE substrate maltose-1-phosphate (M1P). However, Mtb GlgE is difficult to crystallize and affords lower resolution X-ray structures. Sco GlgEI-V279S on the other hand crystallizes readily, produces high resolution X-ray data, and has active site topology identical to Mtb GlgE. We report the X-ray structure of Sco GlgEI-V279S in complex with 2-deoxy-2,2-difluoro-α-maltosyl fluoride (α-MTF, 5) at 2.3 ? resolution. α-MTF was designed as a non-hydrolysable mimic of M1P to probe the active site of GlgE1 prior to covalent bond formation without disruption of catalytic residues. The α-MTF complex revealed hydrogen bonding between Glu423 and the C1F which provides evidence that Glu423 functions as proton donor during catalysis. Further, hydrogen bonding between Arg392 and the axial C2 difluoromethylene moiety of α-MTF was observed suggesting that the C2 position tolerates substitution with hydrogen bond acceptors. The key step in the synthesis of α-MDF was transformation of peracetylated 2-fluoro-maltal 1 into peracetylated 2,2-difluoro-α-maltosyl fluoride 2 in a single step via the use of Selectfluor.

IF5-pyridine-HF, an air- and moisture-stable fluorinating reagent, was applied to the synthesis of glycosyl fluorides from (phenylthio)glycosides. Common protecting groups of alcohol and diol can tolerate the reaction conditions performed, and therefore, the present method is applicable to the synthesis of various glycosyl fluorides.

TnBgl1A from the thermophile Thermotoga neapolitana is a dimeric β-glucosidase that belongs to glycoside hydrolase family 1 (GH1), with hydrolytic activity through the retaining mechanism, and a broad substrate specificity acting on β-1,4-, β-1,3- and β-1,6-linkages over a range of glyco-oligosaccharides. Three variants of the enzyme (TnBgl1A-E349G, TnBgl1A-E349A and TnBgl1A-E349S), mutated at the catalytic nucleophile, were constructed to evaluate their glycosynthase activity towards oligosaccharide synthesis. Two approaches were used for the synthesis reactions, both of which utilized 4-nitrophenyl β-d-glucopyranoside (4NPGlc) as an acceptor molecule: the first using an α-glucosyl fluoride donor at low temperature (35 °C) in a classical glycosynthase reaction, and the second by in situ generation of the glycosyl donor with (4NPGlc), where formate served as the exogenous nucleophile under higher temperature (70 °C). Using the first approach, TnBgl1A-E349G and TnBgl1A-E349A synthesized disaccharides with β-1,3-linkages in good yields (up to 61%) after long incubations (15 h). However, the GH1 glycosynthase Bgl3-E383A from a mesophilic Streptomyces sp., used as reference enzyme, generated a higher yield at the same temperature with both a shorter reaction time and a lower enzyme concentration. The second approach yielded disaccharides for all three mutants with predominantly β-1,3-linkages (up to 45%) but also β-1,4-linkages (up to 12.5%), after 7 h reaction time. The TnBgl1A glycosynthases were also used for glycosylation of flavonoids, using the two described approaches. Quercetin-3-glycoside was tested as an acceptor molecule and the resultant product was quercetin-3,4′-diglycosides in significantly lower yields, indicating that TnBgl1A preferentially selects 4NPGlc as the acceptor.

BrF3-KHF2, an air-stable solid prepared from BrF3 and KHF2, was used in the various fluorination reactions, including desulfurizing fluorination reactions of benzylic sulfides, ketone and aldehyde dithioacetals, (phenylthio)glycosides, and trimethyl trithioorthocarboxylates. As the results, one to three fluorine atoms were selectively introduced to the substrates.

A versatile glycosynthase (TnG-E338A) with strikingly broad substrate scope has been developed from Thermus nonproteolyticus β-glycosidase (TnG) by using site-directed mutagenesis. The practical utility of this biocatalyst has been demonstrated by the facile generation of a small library containing various oligosaccharides and a steroidal glycoside (total 25 compounds) in up to 100 % isolated yield. Moreover, an array of eight gluco-oligosaccharides has been readily synthesized by the enzyme in a one-pot, parallel reaction, which highlights its potential in the combinatorial construction of a carbohydrate library that will assist glycomic and glycotherapeutic research. Significantly, the enzyme provides a means by which glycosynthase technology may be extended to combinatorial chemistry.

In order to utilize ammomium halides (Et4NX, X=Cl, Br, I) as halogenmediator for electrocatalytic fluorination, cyclic voltammetry measurements of the halides were investigated. The catalytic current of the halides in the presence of a dithioacatal compound was observed and the macro-scale electrolysis of dithioacetals using the halogen mediator was also carried out in ionic liquid hydrogen fluoride (HF) salt to give the corresponding fluorinated products in excellent yields. The recycle use of the halogen mediator in the electrochemical fluorination was successfully demonstrated. More inexpensive halides such as potassium bromide and potassium iodide could be soluble in HF salt and worked well as halogen mediator for the electrocatalytic fluorination.

A facile and convenient synthesis of disarmed glycosyl fluorides using in situ-generated iodine monofluoride is reported. The method is tolerant to most of the popularly used protecting groups and gives exclusively the α-anomeric product in very good yields.

Glycosyl fluorides can be synthesized from thio-, seleno-, and telluroglycosides and glycosyl sulfoxides using the aminodifluorosulfinium tetrafluoroborate reagents Xtalfluor-E and -M, with or without added N-bromosuccinimide. Mechanistic studies provide evidence that fluoride is delivered from the tetrafluoroborate counterion.

Mannosides in the southern hemisphere: Conformational analysis of enzymatic mannoside hydrolysis informs strategies for enzyme inhibition and inspires solutions to mannoside synthesis. Atomic resolution structures along the reaction coordinate of an inverting α-mannosidase show how the enzyme distorts the substrate and transition state. QM/MM calculations reveal how the free energy landscape of isolated α-D-mannose is molded on enzyme to only allow one conformationally accessible reaction coordinate. Copyright

Acacetin-7-O-β-d-galactopyranoside (1), a natural flavonoid isolated from flower heads of Chrysanthemum morifolium, has been reported to inhibit the replication of HIV in H9 cells. We achieved the total synthesis of compound 1 by employing a one-pot synthesis of the aglycon. The key reactions in this approach include the modified Baker-Venkataraman reaction and regio- and stereoselective O-glycosylations.

The direct conversion of thioglycosides to glycosyl fluorides frequently used in oligosaccharide synthesis was examined using N,N-diethylaminosulfur trifluoride (DAST). Although the reaction proceeded without N-bromosuccinimide (NBS), in some cases it was found that the electrophilicity of the Vilsmeier-type electrophilic sulfinium cation species was not sufficient for the activation of certain less-reactive thioglycosides. Here, we report the results of fluorination reactions of a series of monosaccharides using DAST in the absence of NBS, and also discuss the acceleration of the reaction in the presence of dimethyl(methylthio)sulfonium trifluoromethanesulfonate (DMTST) resulting in excellent product yields.

Homooligomeric saccharides are of general interest with potential applications in chemical, pharmaceutical, and food industry as well as for materials with novel properties. This contribution describes a methodology of a base-promoted "single step self-oligomerization" of glycosyl fluorides as donors leading to oligomers with up to ～25 saccharide units. The influences of base and reaction time were examined. Linkage analysis of the corresponding alditol acetates by GC/MS allowed for calculation of average structural elements of oligomers.

The X-ray analyses of 2,3,4,6-tetra-O-acetyl-α-D-glucopyran-osyl fluoride, C14H19FO9, (I), and the corresponding maltose derivative 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl-(1→4)- 2,3,6-tri-O-acetyl-α-D-glucopyran-osyl fluoride, C26H 35FO17, (II), are reported. These add to the series of published α-glycosyl halide structures; those of the Peracetylated α-glucosyl chloride [James & Hall (1969). Acta Cryst. A25, S196] and bromide [Takai, Watanabe, Hayashi & Watanabe (1976). Bull. Fac. Eng. Hokkaido Univ. 79, 101-109] have been reported already. In our structures, which have been determined at 140 K, the glycopyranosyl ring appears in a regular 4C1 chair conformation with all the substituents, except for the anomeric fluoride (which adopts an axial orientation), in equatorial positions. The observed bond lengths are consistent with a strong anomeric effect, viz. the C1-O5 (carbohydrate numbering) bond lengths are 1.381 (2) and 1.381 (3) A in (I) and (II), respectively, both significantly shorter than the C5-O5 bond lengths, viz. 1.448 (2) A in (I) and 1.444 (3) A in (II).

The electrochemical fluorination of organosulfur compounds in triethylamine/hydrofluoric acid (Et3N-5HF) with polystyrene-supported iodobenzene (PSIB) and tetraethylammonium chloride (Et4NCl) was performed successfully in an undivided cell under constant current conditions to afford the corresponding fluorinated compounds in moderate to good yields. Recycle use of the PSIB could be achieved due to its easy separation. Notably, the mediatory activity of the iodobenzene derivative was not appreciably changed even after 10 recycle uses.

Di- and tri-saccharides were synthesized on a solid phase. The procedure started with a non-protected sugar linked via either cysteine or glutamine to a polystyrene resin. Selective dimethoxytritylation chemistry and subsequent steps yielded a resin-bound acceptor that could be glycosylated to yield β1,6-linked disaccharides. Reiteration of the procedure produced the trisaccharide.

A method of fluorination comprising reacting monosaccharides, oligosaccharides, polysaccharides, composite saccharides formed by bonding of these saccharides with proteins and lipids and saccharides having polyalcohols, aldehydes, ketones and acids of the polyalcohols, and derivatives and condensates of these compounds with a fluorinating agent represented by general formula (I) thermally or under irradiation with microwave or an electromagnetic wave having a wavelength around the microwave region. In accordance with the method, the fluorination at a selected position can be conducted safely at a temperature in the range of 150 to 200°C where the reaction is difficult in accordance with conventional methods. The above method comprising the irradiation with microwave or an electromagnetic wave having a wavelength around the microwave region can be applied to substrates other than saccharides. When a complex compound comprising HF and a base is reacted under irradiation with microwave, fluorination at a specific position which is difficult in accordance with conventional methods proceeds highly selectively, efficiently in a short time and safely.

Deoxyfluorination of a hydroxy group in carbohydrates was carried out using N,N-diethyl-α,α-difluoro-(m-methylbenzyl)amine. A primary hydroxy group in carbohydrates was effectively converted to the corresponding fluoride under microwave irradiation or at 100°C. Deoxyfluorination of hydroxy groups at the anomeric position proceeded at below room temperature, and glycosyl fluorides could be obtained in good yields. The reaction chemoselectively proceeded, and various protecting groups of carbohydrates can survive under the reaction conditions.

Deoxyfluorination of alcohols was carried out using N,N-diethyl-α, α-difluoro-(m-methylbenzyl)amine (DFMBA). Primary alcohols were effectively converted to fluorides under microwave irradiation or conventional heating. Deoxyfluorination of an anomeric hydroxy group in sugars by DFMBA proceeded at below room temperature and glycosyl fluorides could be obtained in good yields. The deoxyfluorination reaction chemoselectively proceeded and various protecting groups on the sugar can survive under the reaction conditions.

A fast method for the simultaneous detection of different glycosidolytic activities in commercially available enzyme preparations and crude culture filtrates was found in using, as substrate, a mixture of different glycosyl fluorides and 19F NMR spectroscopy as a screening technique. Accompanying studies regarding the hydrolytic stability of these fluorides in various buffer systems, as well as conditions of their long-term storage, were carried out. A simple procedure for the preparation of β-D-mannopyranosyl fluoride in gram quantities is given. Copyright (C) 2000 Elsevier Science Ltd.

Treatment of readily available phenyl 1-selenoglycosides and phenyl 1-telluroglycosides with DAST in the presence of halonium ion activators yields the corresponding glycosyl fluoride in high yield. The stereoselectivity of the conversion is affected by C-2 substituents, stereochemistry of starting glycoside and reaction solvent.

Glycosyl chlorides and bromides can be rapidly converted to glycals in high yield by reaction with (Cp2Ti[III]Cl)2. This reagent tolerates a wide range of common carbohydrate protecting groups, including silyl ethers, acetals, and esters; the methodology provides a general route for the preparation of glycals substituted with both acid- and base-labile functionality. A reaction mechanism is proposed that is based on heteroatom abstraction to give an intermediate glycosyl radical. This radical reacts with a second equivalent of Ti(III) to yield a glycosyltitanium(IV) species. β-Heteroatom elimination from the glycosyltitanium(IV) complex gives the glycal.

The stereospecific formation of α-D-mannosyl glycosidic linkages has been achieved in high yield using tetra-O-pivaloyl-α-D-mannopyranosyl fluoride and boron trifluoride diethyl etherate in dichloromethane. Examples of the α-D-mannosylation of primary, secondary, benzylic and phenolic hydroxyl groups are described. Copyright (C) 1999 Elsevier Science Ltd.

A process for the preparation of a selectively fluorinated organic compound, which process includes reaction of a precursor of said organic compound, the precursor containing at least one Group VI element selected from sulfur, selenium and tellurium, with a fluorinating agent and another halogenating agent and characterized in that the fluorinating agent is elemental fluorine.

A process of preparing mannosylated alcohols or phenols in high chemical yield and purity using tetra-O-pivaloylmannosylfluoride and a Lewis acid catalyst.

Trifluoromethylzinc bromide was used to prepare the corresponding glycosyl fluorides from the peracetylated α-pyranosyl bromides of D-glucose 1, D-galactose 3, D-mannose 5, D-lyxose 7, and L-rhamnose 9, respectively, in good yields. D-Glucopyranosyl bromide 1 and the D-galactopyranosyl bromide 3, exclusively delivered the corresponding β-D-glycosyl fluorides 2β and 4β. The other bromides 5, 7 and 9 formed mixtures of anomeric fluorides (6α/6β, 8α/8β, 10α/10β). Similarily, the anomeric OH-groups of the D-glycopyranoses 11, 12, 13, 15, 17 could be substituted by fluoride using trifluoromethylzinc bromide/titanium tetrafluoride. In all cases mixtures of anomeric fluorides 2α/2β, 6α/6β, 14α/14β, 16α/16β, and 18α/18β were obtained.

Treatment of readily available thio- and selenoglycosides with the reagent 4-methyl(difluoroiodo)benzene leads to the formation of the corresponding fluoroglycosides in moderate to good yield.

1,3-Dithiolanes, prepared from diaryl ketones, react with elemental fluorine-iodine mixtures to give the corresponding difluoromethylene derivatives. Under the same conditions, thioglycosides give glycosyl fluorides in good yields. Reaction of 1,3-dithiolanes with fluorine in aqueous acetonitrile provides a remarkably mild method for efficient deprotection to the parent ketone.

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6-Bromo-6-deoxy-α-D-glucopyranosyl fluoride (2) was prepared in good yield from α-D-glucopyranosyl fluoride (1) by treatment with PPh3 and CBr4 in pyridine.Catalytic reduction of 2 gave the corresponding 6-deoxy-α-D-glucopyranosyl fluoride (3) while treatment with NaN3 in DMF gave the 6-azido-6-deoxy-α-D-glucopyranosyl fluoride (4).The latter could be reduced to the 6-amino-6-deoxyglucosyl fluoride (5) which was converted into the 6-acetamido-6-deoxy-α-D-glucopyranosyl fluoride (6).The C-6 modified glucosyl fluorides 2, 3, 4, and 6 are crystalline compounds.

The syntheses are described of 2,3-di-O-glycosyl derivatives of methyl α- and β-D-glucopyranoside having α-D-manno-, β-D-galacto, α-L-rhamno, α-L-fuco, and β-L-fuco-pyranosyl substituents at O-2 and O-3.The syntheses involved glycosylation of methyl 4,6-O-benzylidene-α- (24) and β-D-glucopyranoside (21), and substituted derivatives of 21 bearing 2-O-(2,3,4,6-tetra-O-benzoyl-α-D-mannopyranosyl)-, -(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-, -(2,3,4-tri-O-benzoyl-α-L-rhamnopyranosyl)-, and -(2,3,4-tri-O-benzoyl-β-L-fucopyranosyl) groups.

The reaction of protected monosaccharides or oligosaccharides or protected monosaccharide and oligosaccharide derivatives containing an anomeric hydroxyl group with secondary α-haloenamines affords high yields of protected glycosyl halides, which are valuable intermediates for the introduction of sugar groups in the synthesis of oligosaccharides, glycolipids or glycopeptides.

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A variety of usefully functionalised 1-fluoroglycosides may be prepared under mild conditions from their corresponding arylthioglycoside derivatives by reaction with 4-methyl(difluoroiodo)benzene.

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The anomeric hydroxyl group of various furanose and pyranose hemiacetals can be replaced by a fluorine, chlorine, bromine or iodine atom under neutral conditions using haloenamines.

The synthesis is described of four pentasaccharides, which are structurally related to the bacterial capsular polysaccharide isolated from E. coli K5 (010/K5/H40), i.e. the so-called K5 antigen.These four synthetic compounds comprise: (i) a pentasaccharide that is structurally identical to the K5 antigen (i.e. compound 16); (ii, iii) two pentasaccharides containing two and three O-sulphated groups respectively on defined positions (i.e. compounds 15a and 15b); (iv) a pentasaccharide that is O-sulphated on all hydroxyl groups (i.e. compound 17).These four K5-antigen-related pentasaccharides were synthesized from the fully protected pentasaccharides 13a and 13b.The preparation of compounds 13a,b was based on coupling of disaccharide 6a with the disaccharide 10a or 10b to give tetrasaccharides 11a,c, respectively, which in turn were coupled to monosaccharide 12.Deblocking of the pentasaccharides 13a,b and conversion into the pentasaccharides 15a and 15b was performed by saponification of the ester functions, O-sulphation, hydrogenalysis and finally selective N-acetylation. compound 16 was obtained from 13a,b by saponification of the ester functions, deblocking of the benzyl and N-protective groups, followed by selective N-acetylation.The persulphated derivative 17 was obtained from 15a by extensive O-sulphation.The structure of the K5-antigen-related pentamers was confirmed by 1H NMR- and 13C NMR-spectroscopical techniques.

Glycosyl halides which are O-acylated or O-alkylated at least in the 2-position are transhalogenated with alkali metal hydrogen difluorides in a polar-aprotic solvent and, if appropriate, the product is anomerized with the addition of less than the stoichiometric amounts of an inorganic fluoride with a Lewis acid character. Depending on the substrate, the glycosyl fluorides with the 1,2-trans or 1,2-cis configuration are obtained.

Glycosylation of 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose (6), as well as its 6-trimethylsilyl ether 7 with 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl fluoride (5) was achieved stereospecifically in a mild and fast manner in the presence of Lewis acids like, e.g., titanium tetrafluoride, to give the β-(16)-linked disaccharide derivative 1.By use of 2,3,4,6-tetra-O-benzyl-β-D-glucopyranosyl fluoride (8) or its α anomer 10 and titanium tetrafluoride in acetonitrile with 6 or 7, a fast reaction proceeds preponderantly to yield 1,2:3,4-di-O-isopropylidene 6-O-(2,3,4,6-tetra-O-benzyl-β-D-glucopyranosyl)-α-D-galactopyranose (2).In ether, however, mainly the α-(16) anomer was formed.These model systems were used to elucidate the limiting conditions for this procedure, and mechanistic conceptions are discussed.By glycosylation at O-4 of 1,6:2,3-dianhydro-β-D-mannopyranose (11) with the perbenzylated α-fluoride 10 both the α- and the β-D-(14) disaccharide derivatives 12 and 14 were obtained, but 5 gave exclusively the β-D-(14) compound 16.Opening of the anhydro rings of 12 led to the synthesis of N-acetyl-maltosamine (22). 1,6-anhydro-2-azido-4-O-benzyl-2-deoxy-β-D-glucopyranose was glycosylated with methyl (2,3,4-tri-O-acetyl-β-D-galactopyranosyl fluoride)uronate under titanium tetrafluoride catalysis to give the β-D-(13)-linked disaccharide 26, subsequently transformed into 29.