Conformational interchange of a carbohydrate by mechanical compression at the air-water interface.

Methyl xylopyranoside containing three 4-(pyrene-1-yl)benzoyl groups (PyXy) undergoes conformational interchange within a Langmuir monolayer upon mechanical compression. This xylose-type molecular machine PyXy was immobilized within two different matrix lipids, methyl stearate and methyl 2,3,4-tri-O-stearoyl-ß-D-xylopyranoside, which respectively form rigid and soft monolayers. Structural properties of the monolayer were characterized by assessing the compressibility, compression modulus, and ideal limiting molecular area of PyXy, all of which were estimated from the π-A isotherm measurements. Only the rigid monolayer exhibited a transition to the condensed phase with a limiting molecular area of PyXy smaller than that of the cross-sectional area of the xylopyranose ring in its C1 chair conformation. This suggests conformational interchange of PyXy from the most stable (4)C1 (C1) form to the metastable (1)C4 (1C) form. Surface-reflective fluorescence spectroscopy of the monolayer was applied to detect excimer emission resulting from the face-to-face dimerization of pyrenes attached at the O-2 and O-4 positions of xylose. Fluorescence intensity of the excimer increased abruptly in the condensed region only when the rigid monolayer was applied. These results indicate that the rigidity of the matrix monolayer is a critical aspect of the precise manipulation of molecular machines at interfaces. Consequently, this study demonstrates that including a molecular machine into a rigid lipid matrix is a promising means for the preparation of a novel nanoassembly with dynamic functionalities variable depending on a mechanical stimulus.

Synthesis of and molecular dynamics simulations on a tetrasaccharide corresponding to the repeating unit of the capsular polysaccharide from Salmonella enteritidis.

Syntheses of two oligosaccharides as methyl glycosides related to the repeating unit of S. enteritidis capsular polysaccharide (CPS) are presented. The trisaccharide corresponds to the backbone of the CPS whereas the tetrasaccharide is a model for the repeating unit which has a branched structure. Molecular dynamics simulations investigating their flexibility and dynamics revealed that the oligosaccharides populate several conformational states and indicate that conformational averaging should be used in describing the accessible conformational space.

Synthesis of 8-azidooctyl glycoside derivatives of the O-chain repeating unit of Escherichia coli O9a lipopolysaccharide and a methylated analog.

Described is the synthesis of 8-azidooctyl glycoside derivatives of the Escherichia coli serotype O9a O-chain tetrasaccharide repeating unit and the terminal tetrasaccharide motif in this polysaccharide, which contains a methyl group on O-3 of the distal mannopyranose residue. The assembly of these compounds involved the sequential addition of monosaccharide residues from the reducing to the nonreducing end of the molecule using glycosyl trichloroacetimidate donors. Both compounds were initially prepared as p-methoxyphenyl glycosides, which were converted to the corresponding 8-azidooctyl derivatives at a late stage in the synthesis.

An alternative method for the rapid synthesis of partially O-methylated alditol acetate standards for GC-MS analysis of carbohydrates.

Mixtures of partially O-methylated alditol acetate standards (PMAAs) of Glc, Gal, and Man were synthesized rapidly. Methylation of methyl glycosides was carried out in the presence of BaO/Ba(OH)(2) x 8H(2)O giving rise to mixtures of partially methylated glycosides (PMGs), whose degree of methylation was monitored by TLC. The batch containing the largest mixture of methyl ethers was converted into partially O-methylated alditol acetate derivatives (PMAAs), via successive hydrolysis, reduction, and acetylation, and then subjected to GC and GC-MS analysis. Detailed data on retention times, TIC, and EIMS are now provided.

Conformational analysis of methyl 5-O-methyl septanosides: effect of glycosylation on conformer populations.

Methyl 5-O-methyl-alpha-d-glycero-d-idoseptanoside (3) and methyl 5-O-methyl-beta-d-glycero-d-guloseptanoside (4) were investigated as (1-->5)-linked di-/oligoseptanoside mimetics. Here we report the synthesis of 3 and 4 and describe their preferred solution conformations through a combination of ab initio/DFT calculations and (1)H (3)J(H,H) NMR coupling constant analysis. The conformations of 3 and 4 observed in this study are discussed in comparison to those of the parent (C5 hydroxy) compounds 1 and 2. The results indicate that methyl 5-O-methyl-alpha-septanoside 3 is relatively rigid and adopts the same (3,4)TC(5,6) conformation as 1. Methyl 5-O-methyl-beta-septanoside 4 is somewhat less rigid than its parent septanoside (2). In addition to the (6,O)TC(4,5) conformation adopted by 2, beta-septanoside 4 also populates the adjacent (3,4)TC(5,6) conformation. Glycosylation at C5 on beta-septanoside 4 therefore increases its overall flexibility and allows access to alternative ring conformations.

Synthesis of a di- and a trisaccharide related to the O-antigen of Escherichia coli O83:K24:H31.

Di- and trisaccharide fragments related to the repeating unit of the O-antigen of Escherichia coli O83:K24:H31 have been synthesized as their methyl glycoside analogs starting from readily available monosaccharides.

Stereocontrolled synthesis of the D- and L-glycero-beta-D-manno-heptopyranosides and their 6-deoxy analogues. Synthesis of methyl alpha-l-rhamno-pyranosyl-(1-->3)-D-glycero-beta-D-manno-heptopyranosyl- (1-->3)-6-deoxy-glycero-beta-D-manno-heptopyranosyl-(1-->4)-alpha-L- rhamno-pyranoside, a tetrasaccharide subunit of the lipopolysaccharide from Plesimonas shigelloides.

The synthesis of d- and l-glycero-alpha-manno-thioheptopyranosides, protected with 4,6-O-alkylidene-type acetals is described. In glycosylations carried out with preactivation with the 1-benzenesulfinylpiperidine/trifluoromethanesulfonic anhydride couple, both the D- and L-glycero series exhibit excellent beta-selectivity with a range of glycosyl acceptors. In contrast, a 4,7-O-alkylidene acetal was found not to afford beta-selectivity. With a 4,6-O-[1-cyano-2-(2-iodophenyl)ethylidene] acetal protected thioglycoside, excellent beta-selectivity was obtained in glycosylation reactions, and subsequent treatment with tributyltin hydride and azoisobutyronitrile brought about clean fragmentation to the 6-deoxy-glycero-beta-D-manno-heptopyranosides. This chemistry was applied to the stereocontrolled synthesis of methyl alpha-L-rhamno-pyranosyl-(1-->3)-D-glycero-beta-D-manno-heptopyranosyl-(1-->3)-6-deoxy-glycero-beta-D-manno-heptopyranosyl-(1-->4)-alpha-L-rhamno-pyranoside, a component of the lipopolysaccharide from Plesimonas shigelloides.

Septanose carbohydrates: synthesis and conformational studies of methyl alpha-D-glycero-D-idoseptanoside and methyl beta-D-glycero-D-guloseptanoside.

We report the synthesis of methyl alpha-D-glycero-D-idoseptanoside (1) and methyl beta-D-glycero-D-guloseptanoside (2) and the characterization of their preferred solution conformations by computational chemistry and (1)H NMR (3)J(H,H) coupling constant analysis. Central to the synthetic approach was the epoxidation of glucose-derived oxepine 3 using DMDO. Nucleophilic attack on the resulting 1,2-anhydroseptanose using NaOCH(3) in CH(3)OH followed by deprotection provided the 1,2-trans diastereomers 1 and 2. The computational approach for determining the preferred low energy septanose conformations began with a pseudo Monte Carlo search for each isomer using minimization with the AMBER force field. Single-point energy calculations (HF/6-31G *and B3LYP/6-31+G**) as well as full geometry optimizations in a model for aqueous solvent were then conducted using the conformers within 5 kcal/mol of the AMBER global minimum. Calculated (3)J(H,H) values, based on a Boltzmann distribution of the computed low energy conformers, were compared to experimental (3)J(H,H) values from (1)H NMR coupling constant analyses. The correlation between calculated and observed values suggest that septanose carbohydrates are not so flexible and should generally prefer one twist-chair (TC) conformation.

Deoxy and deoxyfluoro analogues of acetylated methyl beta-D-xylopyranoside--substrates for acetylxylan esterases.

Four modified substrates for acetylxylan esterases, 2-deoxy, 3-deoxy, 2-deoxy-2-fluoro, and 3-deoxy-3-fluoro derivatives of di-O-acetylated methyl beta-D-xylopyranoside were synthesized via 2,3-anhydropentopyranoside precursors. Methyl 2,3-anhydro-4-O-benzyl-beta-D-ribopyranoside was transformed into methyl 2,3-anhydro-4-O-benzyl-beta-D-lyxopyranoside in three steps. The epoxide ring opening of 2,3-anhydropentopyranosides was accomplished either by hydride reduction or hydrofluorination. Methyl beta-D-xylopyranoside 2,3,4-tri-O-, 2,4-di-O-, and 3,4-di-O-acetates, and the prepared diacetate analogues were tested as substrates of acetylxylan esterases from Schizophyllum commune and Trichoderma reesei. Measurement of their rate of deacetylation pointed to unique structural requirements of the enzymes for the substrates. The enzymes differed particularly in the requirement for the trans vicinal hydroxy group in the deacetylation at C-2 and C-3 and in the tolerance to the presence of trans vicinal acetyl groups esterifying the OH group at C-2 and C-3.

An access to various sulfation patterns in dermatan sulfate: chemical syntheses of sulfoforms of trisaccharide methyl glycosides.

The syntheses are reported for the first time of alpha-L-IdopA2SO(3)-(1-->3)-beta-D-GalpNAc4SO(3)-(1-->4)-alpha-L-IdopA2SO(3)-(1-->OMe), its disulfated analogue alpha-L-IdopA2SO(3)-(1-->3)-beta-D-GalpNAc-(1-->4)-alpha-L-IdopA2SO(3)-(1-->OMe), and of beta-D-GalpNAc4SO(3)-(1-->4)-alpha-L-IdopA2SO(3)-(1-->3)-beta-D-GalpNAc4SO(3)-(1-->OMe), which represent structural fragments of dermatan sulfate, unavailable directly by chemical or enzymatic degradation of the glycosaminoglycan polymer. These molecules were readily obtained from a pair of key disaccharide intermediates, in which the relative difference of stability of the D-GalNAc 4-hydroxy protecting groups (acetate or pivalate) toward saponification conditions allowed access to various sulfoforms from a common precursor. For the preparation of these blocks, the 4-O-pivaloyl-D-galacto moiety was readily obtained through a one-pot stereospecific intramolecular nucleophilic displacement on an easily available 3-O-pivaloyl-D-gluco precursor, and the L-IdoA moiety through selective radical oxidation at C-6 of a L-ido 4,6-diol derivative with oxoammonium salts.

Homologation of methyl 2-azido- and 2-acetamido-3,4-di-O-benzyl-2-deoxy-D-hexopyranosides with allyloxymethylmagnesium chloride.

Methyl 2-azido-2-deoxy-hexodialdo-1,5-pyranosides of the alpha-, beta-D-gluco and alpha-D-manno configuration as well as methyl 2-acetamido-2-deoxy-hexodialdo-1,5-pyranosides of the alpha- and beta-D-gluco configuration, protected at positions 3 and 4 with O-benzyl groups were reacted with an excess of allyloxymethylmagnesium or (phenyldimethylsilyl)methylmagnesium chlorides to afford mixtures of C-6 stereoisomeric heptopyranosides. Configuration of the products separated by column chromatography was assigned by 1H NMR data.

Further evidence for the gelation ability-structure correlation in sugar-based gelators.

Eight methyl glycosides of 4,6-O-benzylidene derivatives of the monosaccharides D-glucose, D-mannose, D-allose and D-altrose were synthesized to systematically study the effect of small configurational changes on the ability to gelate organic solvents. Among the beta anomers, only the D-mannose glycoside exhibits a strong gelation ability, whereas in the alpha-series the D-glucose and D-mannose derivatives act as versatile gelators. Also, as a general rule we found that the beta anomers possess a higher ability to gelate solvents than the alpha anomers. The gelation properties are discussed on the basis of SAXS, FTIR, differential scanning calorimetric (DSC) measurements and scanning electron microscopy (SEM) observations. The temperature-dependent SAXS measurements were carried out to elucidate the sol-gel transition temperature. The present study emphasizes that the saccharide family provides, not only valuable information of the structural requirements for the design of new gelators, but also for molecular assembly systems in general.

Synthesis of acylated methyl beta-D-xylopyranosides and their enzymic deacylations by rabbit serum esterases.

Selective pivaloylations of methyl beta-D-xylopyranoside have been studied under various reaction conditions. Partially pivaloylated products were submitted to additional acetylations. The structures were established by 1H NMR spectroscopy. Representatives of acylated methyl beta-D-xylopyranosides (acyl being pivaloyl, acetyl, or a combination of both) were submitted to hydrolysis catalyzed by rabbit serum and esterases isolated from rabbit serum.

Synthesis of the methyl alpha-glycoside of a trisaccharide mimicking the terminus of the O antigen of Vibrio cholerae O:1, serotype Inaba.

Coupling of methyl 4-amino-4,6-dideoxy-2-O-4-methoxybenzyl-alpha-D-mannopyranoside, obtained from the corresponding 4-azido derivative by treatment with H2S, with 3-deoxy-L-glycero-tetronolactone gave the crystalline methyl 4-(3-deoxy-L-glycero-tetronamido)-4,6-dideoxy-2-O-4-methoxybenzyl- alpha-D- mannopyranoside (7). Subsequent acetylation of 7, followed by O-demethoxybenzylation of the 8 formed gave the crystalline methyl 3-O-acetyl-4,6-dideoxy-4-(2,4-di-O-acetyl-3-deoxy-L-glycero-tetronami do)-alpha- D-mannopyranoside (9), which was used as the key intermediate in the construction of the title trisaccharide. To make a glycosyl donor allowing the extension of the oligosaccharide chain at O-2, compound 9 was converted, via conventional transformations, into 3-O-acetyl-2-O-bromoacetyl-4,6-dideoxy-4-(2,4-di-O-acetyl-3-deoxy-L-glyc ero- tetronamido)-alpha-D-mannopyranosyl chloride (12). Condensation of 12 with 9 afforded the disaccharide 20 having a selectively removable protecting group at O-2(2). The latter was O-debromoacetylated, and the disaccharide nucleophile thus obtained was treated with 2,3-di-O-acetyl-4,6-dideoxy-4-(2,4-di-O-acetyl-3-deoxy-L-glycero-tetr onamido)- alpha-D-mannopyranosyl chloride to give, after O-deacetylation, the target, title trisaccharide. The constituent monosaccharide of the O-specific polysaccharide antigen of Vibrio cholerae serotype Inaba, 4-(3-deoxy-L-glycero-tetronamido)-4,6-dideoxy-D-mannopyranose (18), was obtained from the peracetate of its methyl alpha-glycoside by acetolysis, followed by O-deacetylation. The amorphous compound 18 was characterized by 1H and 13C NMR spectroscopy and through its crystalline alpha-per-O-acetyl derivative.

Synthesis of the methyl alpha-glycosides of some isomalto-oligosaccharides specifically deoxygenated at position C-4.

Methyl alpha-isomaltoside and methyl alpha-isomaltotrioside specifically deoxygenated at position C-4 of various glucopyranosyl units were synthesized by condensation of either 1,6-di-O-acetyl-2,3-di-O-benzyl-4-deoxy-alpha,beta-D-xylo-hexopyranos e (7) or 1,6-di-O-acetyl-2,3,4-tri-O-benzyl-alpha,beta-D-glucopyranose (10) [mediated by silver perchlorate and tin(IV) chloride] with suitably blocked derivatives of methyl alpha-D-glucopyranoside, its 4-deoxy analog 6, or methyl 4'-deoxy alpha-isomaltoside (13), respectively.

Synthesis of specifically deoxygenated analogues of the methyl alpha-glycoside of the intracatenary monosaccharide repeating unit of the O-polysaccharide of Vibrio cholerae O:1.

Treatment of methyl alpha-D-perosaminide (1) with gamma-butyrolactone gave the 2'-deoxy analogue of methyl 4,6-dideoxy-4-(3-deoxy-L-glycero-tetronamido)-alpha-D-mannopyranos ide (13), the methyl alpha-glycoside of the intracatenary monosaccharide repeating unit of the O-polysaccharide of Vibrio cholerae O:1. The analogous 4'-deoxy derivative was obtained by hydrogenolysis of a 4'-chlorodeoxy precursor, obtained by chlorination of methyl 2,3-di-O-benzyl-4-(2-O-benzyl-3-deoxy-L-glycero-tetronamido)-4,6-d ideoxy-alpha- D-mannopyranoside with methanesulfonyl chloride in DMF. To obtain the 3-deoxy analogue of 13, methyl 4-amino-2-O-benzyl-4,6-dideoxy-3-O-p-methoxy-benzyl-alpha-D-mannopyranos ide was converted into methyl 2-O-benzyl-4,6-dideoxy-4-(2,4-di-O-benzyl-3-deoxy-L-glycero-tetronami do)- alpha-D-mannopyranoside, which was deoxygenated via the corresponding 3-O-(imidazol-1-ylthiocarbonyl) derivative. Subsequent catalytic debenzylation gave the deoxy compound (24). In an alternative synthesis, which is also generally useful for the preparation of 4-N-acyl-3-deoxy derivatives of 1, methyl 4-azido-4,6-dideoxy-alpha-D-mannopyranoside was converted through a series of transformations into methyl 4-amino-2-O-benzyl-3,4,6-tri-deoxy-alpha-D-mannopyranoside. Subsequent reaction with 2-O-benzyl-3-deoxy-L-glycero-tetronolactone, followed by hydrogenolysis of the formed tetronamido derivative, gave 24.

Synthesis of methyl glycosides of some alpha-isomalto oligosaccharides specifically deoxygenated at position C-2.

Methyl alpha-isomaltoside and methyl alpha-isomaltotrioside analogues specifically deoxygenated at position C-2 of various glucopyranosyl units were synthesized by condensation of either 6-O-acetyl-3-O-benzoyl-4-O-benzyl-1-O-tert-butyldimethylsilyl-2-deoxy- beta-D-arabino-hexopyranose (trimethylsilyl triflate mediated) or 6-O-acetyl-2,3,4-tri-O-benzyl-alpha-D-glucopyranosyl chloride (mediated by silver carbonate and silver triflate) with suitably blocked derivatives of methyl alpha-D-glucopyranoside, its 2-deoxy analogue, or methyl 2'-deoxy-alpha-isomaltoside.

Synthesis of the methyl glycosides of a tri- and a tetra-saccharide related to heparin and heparan sulphate.

The methyl glycoside of a tetrasaccharide isolated from heparin, methyl O-(alpha-L-idopyranosyluronic acid)-(1-->4)-O-(2-acetamido-2-deoxy-alpha-D- glucopyranosyl)-(1-->4)-O-(beta-D-glucopyranosyluronic acid)-(1-->3)-O-beta-D-galactopyranoside disodium salt and a trisaccharide derivative thereof, methyl O-(alpha-L-idopyranosyluronic acid)-(1-->4)-O-(2-acetamido-2- deoxy-alpha-D-glucopyranosyl)-(1-->4)-O-beta-D-glucopyranosyluronic acid disodium salt, were synthesized using a block-type strategy. A suitable protected disaccharide block of iduronic acid and glucosamine (IdoA-GlcN) was used as a key intermediate for the syntheses and was glycosidated with a protected galactose derivative and a disaccharide block of glucuronic acid and galactose (GlcA-Gal) to give tri- and tetra-saccharide derivatives, respectively. Deprotection gave the target compounds.

Synthesis of trisaccharide methyl glycosides related to fragments of the capsular polysaccharide of Streptococcus pneumoniae type 18C.

The synthesis is reported of methyl 3-O-(4-O-beta-D-galactopyranosyl-alpha-D- glucopyranosyl)-alpha-L-rhamnopyranoside (1), methyl 2-O-alpha-D-glucopyranosyl-4-O-beta-D-glucopyranosyl-beta-D- galactopyranoside (3), methyl 3-O-(4-O-beta-D-galactopyranosyl-alpha-D-glucopyranosyl)-alpha-L- rhamnopyranoside 3"-(sn-glycer-3-yl sodium phosphate) (2), and methyl 2-O-alpha-D-glucopyranosyl-4-O-beta-D- glucopyranosyl-beta-D-galactopyranoside 3-(sn-glycer-3-yl sodium phosphate) (4), which are trisaccharide methyl glycosides related to fragments of the capsular polysaccharide of Streptococcus pneumoniae type 18C ([----4)-beta-D- Glcp-(1----4)-[alpha-D-Glcp-(1----2)]-[Glycerol-(1-P----3)]-beta-D-Galp - (1----4)-alpha-D-Glcp-(1----3)-alpha-L-Rhap-(1----]n). Ethyl 4-O-acetyl-2,3,6-tri-O-benzyl-1-thio-beta-D-glucopyranoside (10) was coupled with benzyl 2,4-di-O-benzyl-alpha-L-rhamnopyranoside (6). Deacetylation of the product, followed by condensation with 2,4,6-tri-O-acetyl-3-O-allyl-alpha-D-galactopyranosyl trichloroacetimidate (18), gave benzyl 2,4-di-O-benzyl-3-O-[2,3,6-tri-O- benzyl-4-O-(2,4,6-tri-O-acetyl-3-O-allyl-beta-D-galactopyranosyl)-alpha- D- glucopyranosyl]-alpha-L-rhamnopyranoside (19). Acetolysis of 19, followed by methylation, deallylation (----22), and further deprotection afforded 1. Condensation of methyl 2,4-di-O-benzyl-3-O-[2,3,6-tri-O-benzyl-4-O-(2,4,6-tri- O-acetyl-beta-D-galactopyranosyl)-alpha-D-glucopyranosyl]-alpha-L- rhamnopyranoside (22) with 1,2-di-O-benzyl-sn-glycerol 3-(triethyl-ammonium phosphonate) (24), followed by oxidation and deprotection, yielded 2. Condensation of ethyl 2,3,4,6-tetra-O-benzyl-1-thio-beta-D-glucopyranoside (27) with methyl 3-O-allyl-4,6-O-benzylidene-beta-D-galactopyranoside (28), selective benzylidene ring-opening of the product, coupling with 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl trichloroacetimidate (31), and deallylation afforded methyl 6-O-benzyl-4-O-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl)-2-O- (2,3,4,6-tetra-O-benzyl-alpha-D-glucopyranosyl)-beta-D-galactopyranoside (33). Deprotection of 33 gave 3, and condensation of 33 with 24, followed by oxidation and deprotection, gave 4.

Free-radical synthesis of 3-(2-cyanoethyl)- and 3-(2-methoxycarbonylethyl)-2,3-dideoxy-alpha-D-erythro-pentofu ranoside and their application in the synthesis of potential antiviral nucleosides.

Free-radical reaction of different carbohydrate educts 2, 5, and 7 with acrylonitrile in the presence of tributyltin hydride and a radical initiator (AIBN) gave the methyl 3-(2-cyanoethyl)-2,3-dideoxypentofuranosides 3a and 6. Similar reaction of 2 with methyl acrylate gave 3-(2-methoxycarbonylethyl)-2,3-dideoxypentofuranose 3b. Nucleoside coupling of 3a with silylated uracil gave an anomeric mixture of beta- and alpha-nucleoside 8 and 9 which were deprotected to give 10 and 11, respectively. Similar reaction of 3b with silylated N4-isobutyrylcytosine gave 12 and 13 which were deprotected to give the final nucleosides 16 and 17, respectively. None of the compounds 10a, 11, 14-17 showed significant activity against HIV.