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

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

Combinatorial Optimization Strategies for 3-Fucosyllactose Hyperproduction in Escherichia coli.

3-Fucosyllactose (3-FL), an important fucosylated human milk oligosaccharide in breast milk, offers numerous health benefits to infants. Previously, we metabolically engineered Escherichia coli BL21(DE3) for the in vivo biosynthesis of 3-FL. In this study, we initially optimized culture conditions to double 3-FL production. Competing pathway genes involved in in vivo guanosine 5'-diphosphate-fucose biosynthesis were subsequently inactivated to redirect fluxes toward 3-FL biosynthesis. Next, three promising transporters were evaluated using plasmid-based or chromosomally integrated expression to maximize extracellular 3-FL production. Additionally, through analysis of α1,3-fucosyltransferase (FutM2) structure, we identified Q126 residues as a highly mutable residue in the active site. After site-saturation mutation, the best-performing mutant, FutM2-Q126A, was obtained. Structural analysis and molecular dynamics simulations revealed that small residue replacement positively influenced helical structure generation. Finally, the best strain BD3-A produced 6.91 and 52.1 g/L of 3-FL in a shake-flask and fed-batch cultivations, respectively, highlighting its potential for large-scale industrial applications.

Bridging the Translation of ICG-1-Maltotriose: A Multimodal Sensor for Monitoring and Detecting Bacterial Infections.

Bacterial infections lack reliable, specific, and quick detection methods, which incur substantial costs to patients and caretakers. Our team conjugated the FDA-approved fluorescent dye indocyanine green (ICG) with a maltotriose sugar, resulting in two highly specific imaging agents (ICG-DBCO-1-Maltotriose and ICG-Amide-1-Maltotriose) for detecting bacterial infections. We then evaluated the two derivatives using fluorescence imaging (FLI), bioluminescence imaging (BLI), and photoacoustic imaging (PAI) in bacterial infection murine models. Our findings indicate that both imaging agents can correlate with and reliably detect the infection site using FLI and PAI for both Gram-negative and Gram-positive strains, with various bacterial loads. Furthermore, the differences in pharmacokinetic (PK) properties between the two agents allow for one to be used for immediate imaging (2-4 h postinjection), while the other is more effective for longitudinal studies (18-40 h postinjection).

Reinvestigation of the internal glycan rearrangement of Lewis a and blood group type H1 epitopes.

Protonated ions of fucose-containing oligosaccharides are prone to undergo internal glycan rearrangement which results in chimeric fragments that obfuscate mass-spectrometric analysis. Lack of accessible tools that would facilitate systematic analysis of glycans in the gas phase limits our understanding of this phenomenon. In this work, we use density functional theory modeling to interpret cryogenic IR spectra of Lewis a and blood group type H1 trisaccharides and to establish whether these trisaccharides undergo the rearrangement during gas-phase analysis. Structurally unconstrained search reveals that none of the parent ions constitute a thermodynamic global minimum. In contrast, predicted collision cross sections and anharmonic IR spectra provide a good match to available experimental data which allowed us to conclude that fucose migration does not occur in these antigens. By comparing the predicted structures with those obtained for Lewis x and blood group type H2 epitopes, we demonstrate that the availability of the mobile proton and a large difference in the relative stability of the parent ions and rearrangement products constitute the prerequisites for the rearrangement reaction.

Structural insights into α-(1→6)-linkage preference of GH97 glucodextranase from Flavobacterium johnsoniae.

Glycoside hydrolase family 97 (GH97) comprises enzymes like anomer-inverting α-glucoside hydrolases (i.e., glucoamylase) and anomer-retaining α-galactosidases. In a soil bacterium, Flavobacterium johnsoniae, we previously identified a GH97 enzyme (FjGH97A) within the branched dextran utilization locus. It functions as an α-glucoside hydrolase, targeting α-(1→6)-glucosidic linkages in dextran and isomaltooligosaccharides (i.e., glucodextranase). FjGH97A exhibits a preference for α-(1→6)-glucoside linkages over α-(1→4)-linkages, while Bacteroides thetaiotaomicron glucoamylase SusB (with 69% sequence identity), which is involved in the starch utilization system, exhibits the highest specificity for α-(1→4)-glucosidic linkages. Here, we examined the crystal structures of FjGH97A in complexes with glucose, panose, or isomaltotriose, and analyzed the substrate preferences of its mutants to identify the amino acid residues that determine the substrate specificity for α-(1→4)- and α-(1→6)-glucosidic linkages. The overall structure of FjGH97A resembles other GH97 enzymes, with conserved catalytic residues similar to anomer-inverting GH97 enzymes. A comparison of active sites between FjGH97A and SusB revealed differences in amino acid residues at subsites +1 and +2 (specifically Ala195 and Ile378 in FjGH97A). Among the three mutants (A195S, I378F, and A195S-I378F), A195S and A195S-I378F exhibited increased activity toward α-(1→4)-glucoside bonds compared to α-(1→6)-glucoside bonds. This suggests that Ala195, located on the Gly184-Thr203 loop (named loop-N) conserved within the GH97 subgroup, including FjGH97A and SusB, holds significance in determining linkage specificity. The conservation of alanine in the active site of the GH97 enzymes, within the same gene cluster as the putative dextranase, indicates its crucial role in determining the specificity for α-(1→6)-glucoside linkage.

Innovative direct introduction-ion mobility-mass spectrometry (DI-IM-MS) approach for fast and robust isomer-specific quantification in a complex matrix: Application to 2'-fucosyllactose (2'-FL) in breast milk.

Identification and specific quantification of isomers in a complex biological matrix by mass spectrometry alone is not an easy task due to their identical chemical formula and therefore their same mass-to-charge ratio (m/z). Here, the potential of direct introduction combined with ion mobility-mass spectrometry (DI-IM-MS) for rapid quantification of isomers as human milk oligosaccharides (HMOs) was investigated. Differences in HMO profiles between various analyzed breast milk samples were highlighted using the single ion mobility monitoring (SIM2) acquisition for high ion mobility resolution detection. Furthermore, the Se+ (secretor) or Se- (non-secretor) phenotype could be assigned to breast milk samples studied based on their HMO contents, especially on the response of 2'-fucosyllactose (2'-FL) and lacto-N-fucopentaose I (LNFP I). The possibility of quantifying a specific isomer in breast milk by DI-IM-MS was also investigated. The standard addition method allowed the determination of the 2'-FL despite the presence of other oligosaccharides, including 3-fucosyllactose (3-FL) isomer in breast milk. This proof-of-concept study demonstrated the high potential of such an approach for the rapid and convenient quantification of isomers in complex mixtures.

Stereoselective Synthesis of the Gal-α-(1→3)-Gal-ß-(1→3)-GlcNAc Trisaccharide: a new Ligand for DCAR and Mincle C-Type Lectin Receptors.

In this work, we have discovered that the Gal-α-(1→3)-Gal-ß-(1→3)-GlcNAc trisaccharide, a fragment of the B antigen Type-1, is a new ligand of two C-type lectin receptors (CLRs) i. e. DCAR and Mincle which are key players in different types of autoimmune diseases. Accordingly, we report here on a straightforward methodology to access pure Gal-α-(1→3)-Gal-ß-(1→3)-GlcNAc trisaccharide. A spacer with a terminal primary amine group was included at the reducing end of the GlcNAc residue thus ensuring the further functionalization of the trisaccharide Gal-α-(1→3)-Gal-ß-(1→3)-GlcNAc.

Total Synthesis of 6-Deoxy-l-talose Containing a Pentasaccharide Repeating Unit of Acinetobacter baumannii K11 Capsular Polysaccharides.

Herein, we report a concise synthetic approach for the first total synthesis of a pentasaccharide repeating unit of Acinetobacter baumannii K11 capsular polysaccharides containing a rare sugar 6-deoxy-l-talose. The pentasaccharide was synthesized in a convergent manner using a [3 + 2] block glycosylation strategy. During this synthetic strive, we used a 2,2,2-trichloroethoxycarbonyl (Troc)-protected monosaccharide unit to achieve a high yield during the glycosylation to synthesize a trisaccharide, and chemoselective deprotection of the Troc group from the trisaccharide was carried out under a mild, pH-neutral condition, keeping the O-glycosidic bond, azido, and acid/base sensitive group intact. A thiotolylglycoside disaccharide donor containing 6-deoxy-l-talose was synthesized for the first time by the armed-disarmed glycosylation method between two thiotolylglycosides.

Structural characterization of a novel fucosylated trisaccharide prepared from bacterial exopolysaccharides and evaluation of its prebiotic activity.

Fucosylated oligosaccharides have promising prospects in various fields. In this study, a fucosylated trisaccharide (GFG) was separated from the acidolysis products of exopolysaccharides from Clavibacter michiganensis M1. Structural characterization demonstrated that GFG consists of glucose, galactose, and fucose, with a molecular weight of 488 Da. Nuclear magnetic resonance analysis showed that it has a different structure than that of 2'-fucosyllactose (2'-FL), even though they have the same monosaccharide composition. In vitro prebiotic experiments were conducted to evaluate the differences in the utilization of three selected carbohydrates by fourteen bacterial strains. In comparison with 2'-FL, GFG could be utilized by more beneficial bacteria, leading to generate more short-chain fatty acids. Moreover, GFG could not promote the proliferation of Escherichia coli. This work describes a novel fucosylated oligosaccharide and its preparation method, and the obtained trisaccharide may serve as a promising candidate for fucosylated human milk oligosaccharides.

Synthetic Zwitterionic Streptococcus pneumoniae Type 1 Oligosaccharides Carrying Labile O-Acetyl Esters.

We herein report the first total synthesis of the Streptococcus pneumoniae serotype 1 (Sp1) oligosaccharide, a unique zwitterionic capsular polysaccharide carrying labile O-acetyl esters. The target oligosaccharides, featuring rare α-2,4-diamino-2,4,6-trideoxy galactose (AAT) and α-galacturonic acids, were assembled up to the 9-mer level, in a highly stereoselective manner using trisaccharide building blocks. The lability of the O-acetyl esters imposed a careful deprotection scheme to prevent migration and hydrolysis. The migration was investigated in detail at various pD values using NMR spectroscopy, to show that migration and hydrolysis of the C-3-O-acetyl esters readily takes place under neutral conditions. Structural investigation showed the oligomers to adopt a right-handed helical structure with the acetyl esters exposed on the periphery of the helix in close proximity of the neighboring AAT residues, thereby imposing conformational restrictions on the AATα1-4GalA(3OAc) glycosidic linkages, supporting the helical shape of the polysaccharide, that has been proposed to be critical for its unique biological activity.

Isomelezitose Overproduction by Alginate-Entrapped Recombinant E. coli Cells and In Vitro Evaluation of Its Potential Prebiotic Effect.

In this work, the trisaccharide isomelezitose was overproduced from sucrose using a biocatalyst based on immobilized Escherichia coli cells harbouring the α-glucosidase from the yeast Metschnikowia reukaufii, the best native producer of this sugar described to date. The overall process for isomelezitose production and purification was performed in three simple steps: (i) oligosaccharides synthesis by alginate-entrapped E. coli; (ii) elimination of monosaccharides (glucose and fructose) using alginate-entrapped Komagataella phaffii cells; and (iii) semi-preparative high performance liquid chromatography under isocratic conditions. As result, approximately 2.15 g of isomelezitose (purity exceeding 95%) was obtained from 15 g of sucrose. The potential prebiotic effect of this sugar on probiotic bacteria (Lactobacillus casei, Lactobacillus rhamnosus and Enterococcus faecium) was analysed using in vitro assays for the first time. The growth of all probiotic bacteria cultures supplemented with isomelezitose was significantly improved and was similar to that of cultures supplemented with a commercial mixture of fructo-oligosaccharides. In addition, when isomelezitose was added to the bacteria cultures, the production of organic acids (mainly butyrate) was significantly promoted. Therefore, these results confirm that isomelezitose is a potential novel prebiotic that could be included in healthier foodstuffs designed for human gastrointestinal balance maintenance.

Contribution of TagA-Like Glycosyltransferases to the Assembly of the Secondary Cell Wall Polysaccharide in Bacillus anthracis.

Bacillus anthracis elaborates a secondary cell wall polysaccharide (SCWP) made of 6 to 12 trisaccharide units. Pyruvyl and acetyl substitutions of the distal unit are prerequisites for the noncovalent retention of 22 secreted Bacillus S-layer (Bsl)-associated proteins bearing an S-layer homology (SLH) domain. Surface display of Bsl proteins contributes to cell separation as well as virulence. Earlier work suggested that TagO initiates the synthesis of SCWP while GneY and GneZ, two UDP-GlcNAc 2-epimerases, synthesize ManNAc that is later incorporated in the repeat unit (→4)-ManNAc-(ß1→4)-GlcNAc-(ß1→6)-GlcNAc-(α1→). In organisms that synthesize wall teichoic acid, TagA catalysts have been shown to form the glycosidic bond ManNAc-(ß1→4)-GlcNAc. Here, we show that genes bas2675 and bas5272, predicted to encode glycosyltransferases of the WecB/TagA/CpsF family (PFAM03808; CAZy GT26), are required for B. anthracis SCWP synthesis and S-layer assembly. Similar to tagO or gneY gneZ mutants, B. anthracis strains depleted of tagA1 (bas5272) cannot maintain cell shape, support vegetative growth, or synthesize SCWP. Expression of tagA2 (bas2675), or Staphylococcus aureus tagA on a plasmid, rescues the nonviable tagA1 mutant. We propose that TagA1 and TagA2 fulfill overlapping and key glycosyltransferase functions for the synthesis of repeat units of the SCWP of B. anthracis. IMPORTANCE Glycosyltransferases (GTs) catalyze the transfer of sugar moieties from activated donor molecules to acceptor molecules to form glycosidic bonds using a retaining or inverting mechanism. Based on the structural relatedness of their catalytic and carbohydrate-binding modules, GTs have been grouped into 115 families in the Carbohydrate-Active EnZyme (CAZy) database. For complex products, the functional assignment of GTs remains highly challenging without the knowledge of the chemical structure of the assembled polymer. Here, we propose that two uncharacterized GTs of B. anthracis belonging to the WecB/TagA/CpsF family incorporate ManNAc in repeat units of the secondary cell wall polymer of bacilli species.

Direct Synthesis of 2,6-Dideoxy-ß-glycosides and ß-Rhamnosides with a Stereodirecting 2-(Diphenylphosphinoyl)acetyl Group.

Anomeric stereocontrol is usually one of the major issues in the synthesis of complex carbohydrates, particularly those involving ß-configured 2,6-dideoxyglycoside and d/l-rhamnoside moieties. Herein, we report that 2-(diphenylphosphinoyl)acetyl is highly effective as a remote stereodirecting group in the direct synthesis of these challenging ß-glycosides under mild conditions. A deoxy-trisaccharide as a mimic of the sugar chain of landomycin E was prepared stereospecifically in high yield. The synthetic potential was also highlighted in the synthesis of Citrobacter freundii O-antigens composed of a [→4)-α-d-Manp-(1→3)-ß-d-Rhap(1→4)-ß-d-Rhap-(1→] repeating unit, wherein the convergent assembly up to a nonasaccharide was realized with a strongly ß-directing trisaccharide donor. Variable-temperature NMR studies indicate the presence of intermolecular H-bonding between the donor and the bulky acceptor as direct spectral evidence in support of the concept of hydrogen-bond-mediated aglycone delivery.

Synthesis of globotriose-modified peptides for the preparation of a colorimetric biosensor to detect Shiga toxins.

Globotriose (Gal-α1, 4-Gal-ß1, 4-Glc) is involved in binding with Shiga toxins (Stxs) produced by Shigella dysenteriae and certain pathogenic Escherichia coli strains which could cause severe gastroenteritis and hemolytic uremic syndrome (HUS). Thus, this trisaccharide group and its derivatives provide potentials in the development of carbohydrate-based diagnostic and therapeutic reagents against bacterial infection. Instead of the tedious chemical synthesis of globotriose or its glycoconjugates, we reported a multi-step (step-wise) enzymatic synthesis system containing glucosyltransferase (ApNGT, E.C. 4.3.3.5), ß-1, 4-galactosyltransferase (LgtB, E.C. 2.4.1.22) and α-1, 4-galactosyltransferase (LgtC, E.C. 2.4.1.44) to produce globotriose-containing glycopeptides. In addition, based on the specific binding between Stxs and globotriose, a cost-efficient, convenient, ultra-sensitive and specific colorimetric biosensor was further constructed to detect Stxs using glycoconjugated Au@Fe-TFPA-COP (globotriose@Au@Fe-TFPA-COP) as a nanoenzyme catalyst. We estimate that this method conveniently applied in the detection of Stx-producing bacteria and associated infectious diseases.

Practical non-enzymatic synthesis of propargyl sialyl-α-(2-3')-lactosamine trisaccharide using minimal protecting groups manipulation.

The trisaccharide, prop-2-ynyl 5-acetamido-3,5-dideoxy-d-glycero-α-d-galacto-2-nonulopyranosylonic acid-(2 â†’ 3)-ß-d-galactopyranosyl-(1 â†’ 4)-2-acetamido-2-deoxy-ß-d-glucopyranoside (9) has been efficiently synthesized in a few steps without the need of conformationally constrained glycosyl donors and acceptors or enzymes. First, using the known prop-2-ynyl 2-acetamido-2-deoxy-6-O-tert-butyldiphenylsilyl-ß-d-glucopyranoside as acceptor (2) and the peracetylated galactosyl trichloroacetimidate (3) as glycosyl donor, followed by protecting groups manipulation, prop-2-ynyl (6-O-tert-butyldiphenylsilyl-ß-d-galactopyranosyl)-(1 â†’ 4)-2-acetamido-2-deoxy-6-O-tert-butyldiphenylsilyl-ß-d-glucopyranoside (6) was synthesized with exclusive O-4 regioselectivity due to steric hindrance of the upper face of the acceptor at O-3. Sialylation with the thiophenyl glycosyl donor (7) afforded the desired trisaccharide with the shortest number of steps and in higher overall yield than previously reported methodologies. The direct use of minimally protected N-acetyl-lactosamine acceptor (6) was critical for the efficient synthesis of the title compound. The propargylic aglycone is suitable for chemical ligation using click chemistry as reported for its (2 â†’ 6) sialylated analog.

A Novel Alginate Lyase: Identification, Characterization, and Potential Application in Alginate Trisaccharide Preparation.

Alginate oligosaccharides (AOS) have many biological activities and significant applications in prebiotics, nutritional supplements, and plant growth development. Alginate lyases have unique advantages in the preparation of AOS. However, only a limited number of alginate lyases have been so far reported to have potentials in the preparation of AOS with specific degrees of polymerization. Here, an alginate-degrading strain Pseudoalteromonasarctica M9 was isolated from Sargassum, and five alginate lyases were predicted in its genome. These putative alginate lyases were expressed and their degradation products towards sodium alginate were analyzed. Among them, AlyM2 mainly generated trisaccharides, which accounted for 79.9% in the products. AlyM2 is a PL6 lyase with low sequence identity (≤28.3%) to the characterized alginate lyases and may adopt a distinct catalytic mechanism from the other PL6 alginate lyases based on sequence alignment. AlyM2 is a bifunctional endotype lyase, exhibiting the highest activity at 30 °C, pH 8.0, and 0.5 M NaCl. AlyM2 predominantly produces trisaccharides from homopolymeric M block (PM), homopolymeric G block (PG), or sodium alginate, with a trisaccharide production of 588.4 mg/g from sodium alginate, indicating its promising potential in preparing trisaccharides from these polysaccharides.

Synthesis of a library of 2-fluoro-2-deoxy-derivatives of the trimannoside methyl α-D-Man-(1 → 3)-[α-D-Man-(1 → 6)]-α-D-Man and the dimannosides methyl α-D-Man-(1 → 3)-α-D-Man and methyl α-D-Man-(1 → 6)-α-D-Man.

A library of sixteen compounds, 1-16, comprising all (mono-, di-, and tri-) 2-fluoro-2-deoxy-derivatives of the N-glycan core trimannoside α-D-Man-(1 â†’ 3)-[α-D-Man-(1 â†’ 6)]-D-Man, including the corresponding 2-fluoro-2-deoxy disaccharide part structures and the non-fluorinated parent compounds, have been synthesized as their α-methyl glycosides for use as tools in 19F NMR-based lectin-carbohydrate interaction studies. Two methyl 2-fluoro-2-deoxy-mannoside acceptors, 21 (3-OH) and 22 (6-OH), were constructed and used in combination with the corresponding non-fluorinated mannose acceptors, 24 (6-OH) and 25 (3-OH), the 2-fluoro-2-deoxy mannosyl bromide donor 18 and the non-fluorinated bromide donor 23 to efficiently afford the target di-and trisaccharides (disaccharides, 2-3 steps, 47-66% overall yield; trisaccharides, 4 steps, 25-40% overall yield).

Understanding the Xylooligosaccharides Utilization Mechanism of Lactobacillus brevis and Bifidobacterium adolescentis: Proteins Involved and Their Conformational Stabilities for Effectual Binding.

Xylooligosaccharides having various degrees of polymerization such as xylobiose, xylotriose, and xylotetraose positively affect human health by interacting with gut proteins. The present study aimed to identify proteins present in gut microflora, such as xylosidase, xylulokinase, etc., with the help of retrieved whole-genome annotations and find out the mechanistic interactions of those with the above substrates. The 3D structures of proteins, namely Endo-1,4-beta-xylanase B (XynB) from Lactobacillus brevis and beta-D-xylosidase (Xyl3) from Bifidobacterium adolescentis, were computationally predicted and validated with the help of various bioinformatics tools. Molecular docking studies identified the effectual binding of these proteins to the xylooligosaccharides, and the stabilities of the best-docked complexes were analyzed by molecular dynamic simulation. The present study demonstrated that XynB and Xyl3 showed better effectual binding toward Xylobiose with the binding energies of - 5.96 kcal/mol and - 4.2 kcal/mol, respectively. The interactions were stabilized by several hydrogen bonding having desolvation energy (- 6.59 and - 7.91). The conformational stabilities of the docked complexes were observed in the four selected complexes of XynB-xylotriose, XynB-xylotetraose, Xyl3-xylobiose, and Xyn3-xylotriose by MD simulations. This study showed that the interactions of these four complexes are stable, which means they have complex metabolic activities among each other. Extending these studies of understanding, the interaction between specific probiotics enzymes and their ligands can explore the detailed design of synbiotics in the future.

Paludibacter propionicigenes GH10 xylanase as a tool for enzymatic xylooligosaccharides production from heteroxylans.

Bioconversion of lignocellulosic biomass into value-added products relies on polysaccharides depolymerization by carbohydrate active enzymes. This work reports biochemical characterization of Paludibacter propionicigenes xylanase from GH10 (PpXyn10A) and its application for enzymatic xylooligosaccharides (XOS) production from commercial heteroxylans and liquor of hydrothermally pretreated corn cobs (PCC). PpXyn10A is tolerant to ethanol and NaCl, and releases xylobiose (X2) and xylotriose (X3) as the main hydrolytic products. The conversion rate of complex substrates into short XOS was approximately 30% for glucuronoxylan and 8.8% for rye arabinoxylan, after only 4 h; while for PCC, PpXyn10A greatly increased unbranched XOS yields. B. adolescentis fermentation with XOS from beechwood glucuronoxylan produced mainly acetic and lactic acids. Structural analysis shows that while the glycone region of PpXyn10A active site is well preserved, the aglycone region has aromatic interactions in the +2 subsite that may explain why PpXyn10A does not release xylose.

The Synthesis of Blood Group Antigenic A Trisaccharide and Its Biotinylated Derivative.

Blood group antigenic A trisaccharide represents the terminal residue of all A blood group antigens and plays a key role in blood cell recognition and blood group compatibility. Herein, we describe the synthesis of the spacered A trisaccharide by means of an assembly scheme that employs in its most complex step the recently proposed glycosyl donor of the 2-azido-2-deoxy-selenogalactoside type, bearing stereocontrolling 3-O-benzoyl and 4,6-O-(di-tert-butylsilylene)-protecting groups. Its application provided efficient and stereoselective formation of the required α-glycosylation product, which was then deprotected and subjected to spacer biotinylation to give both target products, which are in demand for biochemical studies.