Assignment of anomeric structure to carbohydrates through geminal13C-H coupling constants

Stereoselective chemical synthesis of sugar nucleotides via direct displacement of acylated glycosyl bromides

[structure: see text]. The use of Leloir glycosyltransferases to prepare biologically relevant oligosaccharides and glycoconjugates requires access to sugar nucleoside diphosphates, which are notoriously difficult to efficiently synthesize and purify. We report a novel stereoselective route to UDP- and GDP-alpha-D-mannose as well as UDP- and GDP-beta-L-fucose via direct displacement of acylated glycosyl bromides with nucleoside 5'-diphosphates.

Phosphatidylinositol mannosides: Synthesis and adjuvant properties of phosphatidylinositol di- and tetramannosides

Phosphatidylinositol mannosides (PIMs) isolated from mycobacteria have been identified as an important class of glycolipids with significant immune modulating properties. We present here the syntheses of phosphatidylinositol dimannoside (PIM2, 1) and phosphatidylinositol tetramannoside (PIM4, 2) and evaluate their adjuvant properties in a transgenic mouse model. The key step in the synthetic methodology for the synthesis of 2 relies on the selective glycosylation of diol 3 with mannosyl donor 11. Both synthetic PIMs were effective at enhancing IFN-gamma when given as adjuvants with a model antigen, with PIM2 being the more active. These data suggest that in this assay the PIM core structure is responsible for the observed biological activity.

Novel synthesis of alpha-galactosyl-ceramides and confirmation of their powerful NKT cell agonist activity

alpha-Galactosyl-ceramide (1) has been identified as a powerful modulator of immunological processes through its capacity to bind CD1d molecules and specifically activate invariant natural killer (NK)-like T cells (iNKT cells). This paper describes the synthesis of 1, the analogous alpha-galactosyl-ceramide 3, and its short chain analogue 'OCH' (2), by use of the 4,6-di-O-tert-butylsilylene (DTBS) protecting group to produce a powerful alpha-galactosylating agent. In vivo experiments confirmed these compounds to be potent and selective activators of iNKT cells in a CD1d-dependent manner, each inducing a unique profile of cytokine release. This synthesis strategy will permit the generation of novel derivatives for use in the study of the mechanism of iNKT cell activation.

General occurrence of the glucosinolate glucocochlearin within the Cochlearia genus

A natural compound, glucocochlearin, was isolated from the aerial parts of 10 different Cochlearia species. The purification of this compound was achieved through HPLC. The identity of the product was established mainly on the basis of spectroscopic NMR (1H, 13C, COSY, TOCSY, HMQC, HMBC, J-MOD) and high resolution mass spectroscopy data. This compound can be considered as a chemomarker of the genus Cochlearia.

Phosphatidylinositol mannosides: synthesis and suppression of allergic airway disease

Phosphatidylinositol mannoside (PIM) extracts from mycobacteria have been shown previously to suppress allergic airway inflammation in mice. To help determine the structural requirements for activity, PIM1(2) (1), PIM1(6) (2) and PIM2 (3) were synthesized and tested for their ability to suppress cellular inflammation in a mouse model of allergic asthma. The synthetic PIMs were all effective in suppressing airway eosinophilia in the asthma model, with PIM1(6) being the most effective. Suppression of all inflammatory cells monitored was observed, indicating a general blockade of cellular inflammation. Non-mannosylated phosphatidylinositol (PI) had no suppressive effect, indicating that at least one alpha-d-mannopyranosyl residue is necessary for activity. The suppressive effect of the three PIM compounds indicates that other members of this set may be of value in treatment of a range of diseases driven by infiltration of inflammatory cells.

The structure of the O-specific polysaccharide of the lipopolysaccharide from Burkholderia gladioli pv. agaricicola

A neutral O-specific polysaccharide containing d-mannose, d-rhamnose and d-galactose was obtained by mild acid hydrolysis of the lipopolysaccharide of the plant pathogenic bacterium Burkholderia gladioli pv. agaricicola. By means of compositional analyses and NMR spectroscopy, the chemical repeating unit of the polymer was identified as a linear trisaccharide of the structure shown below, in which the mannose residue was quantitatively acetylated at C-2. [carbohydrate structure: see text]

1JCH Correlates with Alcohol Hydrogen Bond Strength

The strength of the H-bond donation by alcohols is reflected in the carbon-hydrogen bond of the H-C-O-H functional group. The one-bond 13C-1H spin-spin coupling constant of hexafluoroisopropanol (HFIP) correlates with the strength of the H-bond in various HFIP-amine complexes with a slope of approximately -0.2 Hz in 1JCH per approximately 1 kJ mol(-1) increase in the H-bond enthalpy. The decrease in 1JCH is attributed to an increased overlap of the H-bonding sigma orbital with the antibonding sigma orbitals of the vicinal C-H bonds.

Monosaccharides as internal probes for the determination of the absolute configuration of 2-butanol

D-Glucose, D-mannose and L-rhamnose were reacted with a racemic mixture of 2-butanol, and the resulting alpha-glycosides were analyzed by 1H NMR with COSY and NOESY experiments. Conformational analysis of alpha-glycosidic bonds performed with molecular modeling and appropriate heteronuclear long-range coupling measurements and combined with analysis of dipolar couplings observed in NOESY spectra allowed the assignment of absolute configuration in the aglycones of elucidated alpha-glycosides.

Steroidal saponins from Calamus insignis, and their cell growth and cell cycle inhibitory activities

Three novel spirostanol-type (2, 3, and 5) and a furostanol-type (4) steroidal saponins were isolated from the stems of Calamus insignis (Palmae), along with a known steroidal saponin (1) by bioassay guided purification. The chemical structures of 1-5 were established on the basis of spectroscopic analysis and the result of acidic hydrolysis. Compounds 1, 2, 3, and 5 showed cell growth inhibitory activity against HeLa cells at a concentration of less than 10 microM, and 1 exhibited a cell cycle inhibitory effect at the G2/M stage at concentrations of 1.5 and 2.9 microM by flow cytometric analysis. This effect seems to be correlated with large expression of p21 and inhibition of dephosphorylation of cdc2 according to the result of Western blotting analysis.

The structure of a putative exopolysaccharide of Burkholderia gladioli pv. agaricicola

A putative capsular polysaccharide containing D-rhamnose was isolated from the phytopathogenic bacterium Burkholderia gladioli pv. agaricicola by phenol/water extraction followed by ultracentrifugation of the separated water phase and gel-permeation chromatography of the thus obtained supernatant. By means of chemical analyses and NMR spectroscopy, the repeating unit of the polymer was shown to be a linear tetrasaccharide with the structure. [carbohydrates: see text].

Structure of an acidic polysaccharide from the marine bacterium Pseudoalteromonas aliena type strain KMM 3562T containing two residues of l-serine in the repeating unit

The structure of an acidic polysaccharide from Pseudoalteromonas aliena type strain KMM 3562(T) has been elucidated. The polysaccharide was studied by component analysis, (1)H and (13)C NMR spectroscopy, including 2D NMR experiments. A (1)H, (13)C band-selective constant-time heteronuclear multiple-bond connectivity experiment was used to determine amide linkages, between serine and uronic acid (UA) residues, via (3)J(H,C) correlations between Ser-alphaH and UA-C-6. It was found that the polysaccharide consists of pentasaccharide repeating units with the following structure: [carbohydrate structure]; see text.

Caprazamycins, Novel Lipo-nucleoside Antibiotics, from Streptomyces sp

Novel antibiotics, active against acid-fast bacteria, caprazamycins, were isolated from the culture broth of Streptomyces sp. MK730-62F2. The planar structures of the compounds were determined by 2D NMR spectroscopic study. Furthermore, the absolute structure of caprazamycin B (2) was established by NMR spectroscopy and X-ray crystallography of its degradation products and by total synthesis of the 5-amino-5-deoxy-D-ribose moiety. In the course of degradation studies of 2 under alkaline and acidic conditions, we obtained the two core components, caprazene (11) and caprazol (14), respectively, in high yield. Structurally, caprazamycins belong to a family of lipouridyl antibiotics, which have been discovered as specific inhibitors of a bacterial translocase.

Developing high affinity oligosaccharide inhibitors: conformational pre-organization paired with functional group modification

Intramolecular tethering combined with functional group modification has been investigated as an approach to design high affinity oligosaccharide ligands. The preceding paper reported successful tethering to constrain a trisaccharide in the conformation of its bound state with an antibody and thereby achieved a 15-fold increase in association constant. Here we report the synthesis of two beta-alanyl tethered derivatives that employ monochlorination and monodeoxygenation strategies to create inhibitors that should enhance the binding affinity of the target molecules by an additional 10-25-fold, provided that free energy changes are additive when tethering is paired with functional group changes. The binding parameters of the new ligands were measured by isothermal titration calorimetry and the results rationalized with molecular dynamics calculations and a simple docking analysis. The data indicate that while the alanine tether is a reasonable method to constrain trisaccharide , free energy gains obtained by pairing it with functional group modification are not additive and in one case counter-productive.

The design, synthesis and evaluation of high affinity macrocyclic carbohydrate inhibitors

Carbohydrate-protein interactions have been investigated for a model system of a monoclonal antibody, SYA/J6, which binds a trisaccharide epitope of the O-polysaccharide of the Shigella flexneri variant Y lipopolysaccharide. The thermodynamics of binding for the methyl glycoside of the native trisaccharide epitope, Rha-Rha-GlcNAc () to SYA/J6 over a range of temperatures exhibits strong, linear enthalpy-entropy compensation and a negative heat capacity change (DeltaC(p)=-152 cal mol(-1) degree(-1)). At 293 K the free energy of association is the sum of favourable enthalpy and entropy contributions (DeltaH=-3.9 kcal mol(-1) and -TDeltaS=-2.9 kcal mol(-1)). Crystal structures for SYA/J6 Fab detailed the position of the native trisaccharide epitope, Rha-Rha-GlcNAc, and facilitated a strategy to design a tighter binding, low molecular weight ligand. This involved pre-organization of the native trisaccharide in its bound conformation by addition of intramolecular constraints (a beta-alanyl or glycinyl tether). ELISA measurements indicated that the glycinyl tethered trisaccharide was not an optimal candidate for further analysis, while microcalorimetry provided data showing that the beta-alanyl tethered trisaccharide displayed a 15-fold increase in affinity for SYA/J6. Tethering resulted in a favourable entropic contribution to binding, relative to the native trisaccharide (-TDeltaDeltaS=-1.2 kcal mol(-1)). Potential energy and dynamics calculations using the AMBER Plus force fields indicated that trisaccharide adopted a rigid conformation similar to that of the bound conformation of the native trisaccharide epitope. While this strategy resulted in modest free energy gains by minimizing losses due to conformational entropy, thermodynamic data are consistent with significant contributions from solvent reorganization.

New chlorogenin hexasaccharide isolated from Agave fourcroydes with cytotoxic and cell cycle inhibitory activities

A new chlorogenin hexasaccharide (1) was isolated from leaves of Agave fourcroydes (Agavaceae). The structure of the new saponin was elucidated as chlorogenin 3-O-[alpha-L-rhamnopyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->3)-[beta-D-glucopyranosyl-(1-->3)-beta-D-glucopyranosyl-(1-->2)]-beta-D-glucopyranosyl-(1-->4)-beta-D-galactopyranoside] (1) by spectroscopic analysis and the result of acidic hydrolysis. The new saponin (1) as well as known hexasaccharides (3 and 5) isolated here showed cytotoxicity against HeLa cells, and 1 exhibited a cell cycle inhibitory effect at the G2/M stage at the concentration of 7.5 and 10 microg/mL.

Efficient Route to 2-Deoxy β-O-Aryl-d-Glycosides via Direct Displacement of Glycosyl Iodides

[reaction: see text]. The conversion of glycals to 2-deoxy glycosyl acetates followed by reaction with trimethylsilyl iodide affords the corresponding glycosyl iodides, which readily undergo substitution with aryl alkoxy anions to provide 2-deoxy-beta-O-aryl glycosides. Direct displacement of the anomeric iodide alleviates the need to introduce temporary C-2 stereodirecting groups that require subsequent removal. The only observable byproducts from the glycosylations result from elimination of HI giving the starting glycals, which can be recycled through the reaction sequence.

Hydroxymethyl rotamer populations in disaccharides

Sixteen methyl glucopyranosyl glucopyranoside disaccharides (methyl beta-d-Glcp(p-Br-Bz)-(1-->x)-beta/alpha-d-Glcp) containing beta-glycosidic linkages (1-->2, 1-->3, 1-->4, and 1-->6) were synthesized and analyzed by means of CD and NMR spectroscopy in three different solvents. For each of these four types of disaccharides, a correlation was observed between the hydroxymethyl rotational populations around the C5-C6 bond of the glucopyranosyl residue II with the substituents and the anomeric configuration of the methoxyl group in residue I, as well as with the solvent. Nonbonded interactions, the stereoelectronic exo-anomeric effect, and hydrogen bonding were found to be responsible for the observed rotameric differences. Whereas the rotational populations of the (1-->6)-linked disaccharides are mainly dependent on the exo-anomeric effect, the (1-->2)-bonded disaccharides are strongly dependent on the anomeric configuration at C1, and the (1-->3)- and (1-->4)-linked disaccharides are mainly dependent on the substituents and the solvent. The population of the gt rotamer decreases as nonbonded interactions increase but increases as the exo-anomeric effect becomes greater, as well as in the presence of intramolecular hydrogen bonding to the endocyclic oxygen O5'. Comparison of the hydroxymethyl rotational preferences between our model disaccharides revealed a dependence on the glycosidic linkage type. Thus the population of the gg and gt rotamers decreases/increases from (1-->2)- (beta series), to (1-->6)-, to (1-->2)- (alpha series), to (1-->4)-, and to (1-->3)-bonded disaccharides respectively, while the tg rotamer population remains almost constant (around 20%), except for the (1-->3)- and (1-->4)-linked disaccharides with the intramolecular hydrogen bonding to O5', where this population decreases to 10%.

Efficient selective preparation of methyl-1,2,4-tri-O-acetyl-3-O-benzyl-beta-L-idopyranuronate from methyl 3-O-benzyl-L-iduronate

Methyl 1,2,4-tri-O-acetyl-3-O-benzyl-L-idopyranuronate 6beta/6alpha, prepared from methyl 3-O-benzyl-L-iduronate (4), is a key synthon in heparin/heparan sulfate synthesis. The 1H and 13C NMR spectra of the furanose-pyranose mixture of 4, after dissolution and equilibration in d(4)-methanol, were fully assigned allowing to expect that 4 could crystallise in the beta-pyranose form. New acetylation conditions able to trap this form were subsequently devised, allowing the isolation of 83% of pure 6beta by simple crystallisation, along with 9% of the 6beta/6alpha mixture. This represents a major advantage over the previously published procedure, especially on multigram scales.

Solvent effect on the isomeric equilibrium of carbohydrates: the superior ability of 2,2,2-trifluoroethanol for intramolecular hydrogen bond stabilization

The higher aptitude of 2,2,2-trifluoroethanol for intramolecular hydrogen bond stabilization in carbohydrates is suggested. This belief, arising from the analysis by 1H NMR spectroscopy of the solvent effect of D2O, DMSO-d6, and 2,2,2-trifluoroethanol-d3 on the isomeric equilibrium of caryophyllose, was also confirmed by shifting of the conformational equilibria of beta-ribopyranose and of its methyl glycoside.

A new antioxidant monoterpene glycoside, alpha-benzoyloxypaeoniflorin from Paeonia suffruticosa

Alpha-benzoyloxypaeoniflorin (1), a new antioxidant monoterpene alpha-glycoside anomer was isolated from Paeonia suffruticosa along with known compounds, beta-benzoyloxypaeoniflorin (2), paeonolide, paeoniflorin and mudanpioside H. The structure of 1 has been determined by comparing spectral data with those of beta-benzoyloxypaeoniflorin (2). Compound 1 exhibited moderately potent radical scavenging activity on DPPH radical.

The O-polysaccharide of lipopolysaccharide isolated from Vibrio fluvialis O19 is identical to that of Vibrio bioserogroup 1875 variant

A structural analysis has been carried out on the O-polysaccharide of lipopolysaccharide (LPS) isolated from Vibrio fluvialis 181-86 (Kobe) serotype O19 (O19) which has the Inaba antigen factor C of O1 V. cholerae and factors D and E in common with Vibrio bioserogroup 1875. The O-polysaccharide of O19 was characterized as an alpha (1-->2)-linked homopolymer of N-3-hydroxypropionyl-D-perosamine (4-amino-4,6-dideoxy-D-mannopyranose), which was identical to that of Vibrio bioserogroup 1875 Variant. Passive hemolysis and passive hemolysis inhibition analysis performed using anti-factor D, E and anti-factor E antisera, demonstrated that the LPS from O19 harbored O-antigenic factors identical to those of the LPS from Vibrio bioserogroup 1875 Variant.

Novobiocin-related compounds: synthesis of 3-benzoylamino-2-oxo-2H-1-benzopyran-7-yl D-glycopyranosides by the trichloroacetimidate methodology

A general stereoselective method for the synthesis of 4-deoxynovobiocin-related glycosides is described. 3-Benzoylamino-2H-1-benzopyran-7-yl 2,3,4,6-tetra-O-acetyl-D-glycopyranosides of glucose, galactose and mannose were synthesised from appropriate O-glycosyltrichloroacetimidates and N-(7-hydroxy-2-oxo-2H-1-benzopyran-3-yl)benzamides in boiling methylene chloride in the presence of boron trifluoride etherate. Heating of these products in a mixture of triethylamine and methanol gave the corresponding deprotected 3-benzoylamino-2-oxo-2H-1-benzopyran-7-yl beta-D-glycopyranosides.

Synthesis of alpha-galactosylated fragments related to the core-structure of the GPI anchor of Trypanosoma brucei

A series of octyl glycosides di- to tetrasaccharides related to the GPI anchor of Trypanosoma brucei was prepared. Treatment of octyl 2-O-benzoyl-4,6-O-(1,1,3,3-tetraisopropyl-1,3-disiloxane-1,3 -diyl)-alpha-D-mannopyranoside with ethyl 2,3,4,6-tetra-O-benzyl-1-thio-beta-D-galactopyranoside under activation with bromine and silver trifluoromethanesulfonate afforded the alpha-linked disaccharide octyl 2-O-benzoyl-3-O-(2,3,4,6-tetra-O-benzyl-alpha-D-galactopyranosyl)-4,6-O- (1,1,3,3-tetraisopropyl-1,3-disiloxane-1,3-diyl)-alpha -D-mannospyranoside, the siloxane ring of which was regioselectively opened with a HF-pyridine complex to give the disaccharide acceptor octyl 3-O-(2,3,4,6-tetra-O-benzyl-alpha-D-galactopyranosyl)-2-O-benzoyl-4-O-(3 -fluoro-1,1,3,3-tetraisopropyl-1,3-disiloxane-3-yl)-alpha-D- mannopyranoside (4). Mannosylation of 4 with benzobromomannose (7), followed by fluoride catalyzed desilylation gave the trisaccharide octyl 2-O-benzoyl-6-O-(2,3,4,6-tetra-O-benzoyl-alpha-D-mannopyranosyl)-3-O-(2, 3,4,6-tetra-O-benzyl-alpha-D-galactopyranosyl)-alpha-D-mannospyranosi de, which was deblocked via the deacylated intermediate octyl 3-O-(2,3,4,6-tetra-O-benzyl-alpha-D-galactopyranosyl)-6-O-(alpha-D-manno pyranosyl)-alpha-D-mannospyranoside to afford the octyl glycoside trisaccharide octyl 3-O-(alpha-D-galactopyranosyl)-6-O-(alpha-D-mannopyranosyl)-alpha-D-m annospyranoside. Glycosylation of 4 with 3,4,6-tri-O-acetyl-2-O-(2,3,4,6-tetra-O-benzoyl-alpha-D-mannopyranosyl)- alpha-D-mannopyranosyl trichloroacetimidate resulted in the tetrasaccharide octyl 2-O-benzoyl-4-O-(1-fluoro-1,1,3,3-tetraisopropyl-1,3-disiloxane -3-yl)-3-O-(2,3,4,6-tetra-O-benzyl-alpha-D-galactopyranosyl)-6-O-[2-O -(2,3,4,6-tetra-O-benzoyl-alpha-D-mannopyranosyl)-3,4,6-tri-O-acetyl-alp ha-D-mannopyranosyl]-alpha-D-mannospyranoside, sequential desilylation, deacylation and debenzylation, respectively, of which via the intermediate octyl 2-O-benzoyl-3-O-(2,3,4,6-tetra-O-benzyl-alpha-D-galactopyranosyl)-6-O-[2 -O-(2,3,4,6-tetra-O-benzoyl-alpha-D-mannopyranosyl)-3,4,6-tri-O-acetyl-a lpha-D-mannopyranosyl]-alpha-D-mannospyranoside afforded the octyl glycoside tetrasaccharide octyl 3-O-(alpha-D-galactopyranosyl)-6-O-[2-O-(alpha-D-mannopyranosyl)-alpha-D -mannopyranosyl]-alpha-D-mannospyranoside.

Structural study of the exopolysaccharide produced by a clinical isolate of Burkholderia cepacia

The primary structure of the exopolysaccharide produced by a clinical isolate of the bacterium Burkholderia cepacia was studied by means of methylation analysis, selective degradation, NMR spectroscopy, and electrospray mass spectrometry. The resulting data showed that the parent repeating unit of the exopolysaccharide is a highly branched heptasaccharide with the following structure: Two acetyl groups are present per repeating unit, as noncarbohydrate substituents.

Structural characterization of the pectic polysaccharide rhamnogalacturonan II: evidence for the backbone location of the aceric acid-containing oligoglycosyl side chain

Monomeric rhamnogalacturonan II (mRG-II) was isolated from red wine and the reducing-end galacturonic acid of the backbone converted to L-galactonic acid by treatment with NaBH4. The resulting product (mRG-II'ol) was treated with a cell-free extract from Penicillium daleae, a fungus that has been shown to produce RG-II-fragmenting glycanases. The enzymatically generated products were fractionated by size-exclusion and anion-exchange chromatographies and the quantitatively major oligosaccharide fraction isolated. This fraction contained structurally related oligosaccharides that differed only in the presence or absence of a single Kdo residue. The Kdo residue was removed by acid hydrolysis and the resulting oligosaccharide then characterized by 1- and 2D 1H NMR spectroscopy, ESMS, and by glycosyl-residue and glycosyl-linkage composition analyses. The results of these analyses provide evidence for the presence of at least two structurally related oligosaccharides in the ratio approximately 6:1. The backbone of these oligosaccharides is composed of five (1-->4)-linked alpha-D-GalpA residues and a (1-->3)-linked L-galactonate. The (1-->4)-linked GalpA residue adjacent to the terminal non-reducing GalpA residue of the backbone is substituted at O-2 with an apiosyl-containing side chain. Beta3-L-Araf-(1-->5)-beta-D-DhapA is likely to be linked to O-3 of the GalpA residue at the non-reducing end of the backbone in the quantitatively major oligosaccharide and to O-3 of a (1-->4)-linked GalpA residue in the backbone of the minor oligosaccharide. Furthermore, the results of our studies have shown that the enzymically generated aceryl acid-containing oligosaccharide contains an alpha-linked aceryl acid residue and a beta-linked galactosyl residue. Thus, the anomeric linkages of these residues in RG-II should be revised.

Deuterium nuclear spin-lattice relaxation times and quadrupolar coupling constants in isotopically labeled saccharides

(13)C and (2)H spin-lattice relaxation times have been determined by inversion recovery in a range of site-specific (13)C- and (2)H-labeled saccharides under identical solution conditions, and the data were used to calculate deuterium nuclear quadrupolar coupling constants ((2)H NQCC) at specific sites within cyclic and acyclic forms in solution. (13)C T(1) values ranged from approximately 0.6 to 8.2 s, and (2)H T(1) values ranged from approximately 79 to 450 ms, depending on molecular structure (0.4 M sugar in 5 mM EDTA (disodium salt) in (2)H(2)O-depleted H(2)O, pH 4. 8, 30 degrees C). In addition to providing new information on (13)C and (2)H relaxation behavior of saccharides in solution, the resulting (2)H1 NQCC values reveal a dependency on anomeric configuration within aldopyranose rings, whereas (2)H NQCC values at other ring sites appear less sensitive to configuration at C1. In contrast, (2)H NQCC values at both anomeric and nonanomeric sites within aldofuranose rings appear to be influenced by anomeric configuration. These experimental observations were confirmed by density functional theory (DFT) calculations of (2)H NQCC values in model aldopyranosyl and aldofuranosyl rings.

Sequence specific analysis of the heterogeneous glycan chain from peanut peroxidase by 1H-NMR spectroscopy

The cationic peanut peroxidase is a complex enzyme consisting of a heme group, two calcium ions and three complex carbohydrate chains at positions Asn60, 144 and 185. Details of the heme and calcium ligation, necessary for oxidation, have recently been revealed from the three-dimensional structure of the peroxidase. However, the three glycans that may be important for the stability of the enzyme as well as its activity were not resolved. In order to determine the configuration of one of these glycans, PNGase A was used to cleave the glycan from the enzyme at Asn-144. This glycan was studied by two dimensional 1H-NMR spectroscopy to identify the sugar linkages. The results indicated a glycan structure comprising a Man alpha1-6(Xyl beta1-2)Man beta1-4GlcNAc beta1-4(Fuc alpha1-3)GlcNAc beta core but with an additional Man alpha1-3 appendage linked to Man3. The glycan also appeared to be heterogeneous as was noted from a single terminating galactose being linked to approximately 20-25% glycan.

Glyceroglycolipids preventing tert-butylhydroperoxide-induced cell death from Microbacterium sp. and Corynebacterium aquaticum strains

Galactosyl diacylglycerols M874B and S365B obtained from the recently isolated bacteria identified as Microbacterium sp. M874 and Corynebacterium aquaticum S365 were found to prevent oxidative cell death induced by tert-butylhydroperoxide. Their structures were determined to be 1,2-di-O-(12-methyltetradecanoyl)-3-O-beta-D-galactopyranosyl-sn-glycerol and 1-O-(14-methylhexadecanoyl)-2-O-(12-methyltetradecanoyl)-3-O-beta-D-galactopyranosyl-sn-glycerol, respectively.

Partially acetylated tri- and tetrarhamnoside dodecanyl ether derivatives from Cleistopholis patens

Three new partially acetylated derivatives of 1-O-dodecanyl-alpha-L- rhamnopyranosyl-(1-->3)-alpha-L-rhamnopyranosyl-(1-->3)-alpha-L- rhamnopyranoside and three partially acetylated derivatives of 1-O-dodecanyl-alpha-L-rhamnopyranosyl-(1-->3)- alpha-L-rhamnopyranosyl-(1-->3)-alpha-L-rhamnopyranosyl-(1-->4)- alpha-L-rhamnopyranoside, one of them new, have been isolated from the mature leaves of Cleistopholis patens (Annonaceae). Their structures, elucidated by using COSY, COSY-LR, TOCSY and FAB mass spectrometry, have been characterised as cleistrioside-2, -3, -4 and cleistetroside-1, -2 and -6. From the same source, shikimic acid was also isolated.

Structural elucidation of a novel exopolysaccharide produced by a mucoid clinical isolate of Burkholderia cepacia. Characterization of a trisubstituted glucuronic acid residue in a heptasaccharide repeating unit

The structure of the exopolysaccharide (EPS) produced by a clinical isolate of Burkholderia cepacia isolated from a patient with fibrocystic lung disease has been investigated. By means of methylation analyses, carboxyl reduction, partial depolymerization by fuming HCl and chemical degradations such as Smith degradation, lithiumethylenediamine degradation and beta-elimination, supported by GC/MS and NMR spectroscopic analyses, the repeat unit of the EPS has been identified and was shown to correspond to the acidic branched heptasaccharide with the following structure: [formula: see text]. This partially acetylated acidic polymer, distinguished by the presence of the less usual D-isomer of rhamnose and of a trisubstituted glucuronic acid residue, could represent the main EPS produced by this bacterial species.

A simple synthesis of 8-(methoxycarbonyl)octyl 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside and derivatives and their use in the preparation of neoglycoconjugates

8-(Methoxycarbonyl)octyl 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside (10) was synthesized in 54% yield by regioselective diglycosylation of unprotected mannoside 4, employing the trichloroacetimidate donor 1, followed by debenzoylation. Derivatives of compounds 4 and 10 were used to prepare conjugates containing fluorochromes for the study of carbohydrate-lectin interactions, as well as conjugates with phospholipids for the preparation of liposomes.