Total synthesis of sialylated and sulfated oligosaccharide chains from respiratory mucins

The total syntheses of several complex oligosaccharide moieties that occur in the core structure of sulfated mucins are reported. A trisaccharide acceptor was obtained through regio- and stereoselective sialylation of methyl (6-O-pivaloyl-beta-D-galactopyanosyl)(1-->3)-4,6-O-benzylidene-2-a cetamido-2-deoxy-alpha-D-galactopyranoside with a novel sialyl donor. A tetrasaccharide, pentasaccharide, and hexasaccharide were constructed in predictable and controlled manner with high regio- and stereoselectivity after the successful preparation and employment of a disaccharide donor, trisaccharide donor, disaccharide acceptor, and trisaccharide acceptor building blocks. Finally, a mild oxidative cleaving method was adopted for the selective removal of 2-naphthylmethyl (NAP) in the presence of benzyl groups.     

猴头菌寡糖的分离及其结构确定

报道了从猴头菌浸膏中分离出猴头菌二糖和三糖, 并确定了其化学结构.     

A galabiose-based two-dimensional scaffold for the synthesis of inhibitors targeting P- and P-antigen binding proteins

A disaccharide scaffold based on galabiose (Galα1-4Gal) was synthesized. Four different acceptors were evaluated in the α-galactosylation and a relationship between the nucleophilicity, yield, and α/β-selectivity was found. The scaffold contains two orthogonal derivatisation sites, i.e. at O-2′ and the anomeric position, and as proof of concept, one derivatised galabioside was synthesized. Compounds based on this galabiose-scaffold are potential inhibitors of P- and P^k-antigen binding proteins.     

Synthesis of the non-reducing end trisaccharide of the antithrombin-binding domain of heparin and its bioisosteric sulfonic acid analogues

A glucoronic acid-containing trisaccharide related to the antithrombin-binding DEFGH domain of heparin and its methanesulfonic acid analogues were synthesized. Trisaccharides without sulfonic acid content or possessing a sulfonatomethyl moiety at position 2 or 6 of unit F were prepared in high yields by [DE+F] couplings using the same disaccharide uronate donor, respectively. Synthesis of the trisaccharide with a 3-deoxy-3-sulfonatomethyl function was accomplished in three different pathways, from which a [D+EF] coupling and applying a non-oxidized precursor of the glucuronic acid afforded the trisaccharide in the highest yield.     

Synthesis of 3″- and 4″-deoxy-Lewisx trisaccharides: A useful tool for study of carbohydrate-carbohydrate interaction

Synthesis of 3″-deoxy and 4″-deoxy Lewis^x trisaccharides is described. Phenyl 2,3,6-tri-O-benzoyl-4-deoxy-1-thio-β-d-xylo-hexopyranoside was condensed with a diol of glucosamine to give regio- and stereo-selectively a disaccharide. Stereoselective fucosylation of this disaccharide provided a protected deoxy Lewis^x trisaccharide which was deprotected to give the 4″-deoxy Lewis^x trisaccharide. Application of the similar synthetic sequence provided the 3″-deoxy Lewis^x trisaccharide.     

Modular synthesis of heparin oligosaccharides

A general, modular strategy for the first completely stereoselective synthesis of defined heparin oligosaccharides is described. Six monosaccharide building blocks (four differentially protected glucosamines, one glucuronic and one iduronic acid) were utilized to prepare di- and trisaccharide modules in a fully selective fashion. Installation of the alpha-glucosamine linkage was controlled by placing a conformational constraint on the uronic acid glycosyl acceptors thereby establishing a new concept for stereochemical control. Combination of disaccharide modules to form trans-uronic acid linkages was completely selective by virtue of C2 participating groups. Coupling reactions between disaccharide modules exhibited sequence dependence. While the union of many glucosamine uronic acid disaccharide modules did not meet any problems, certain sequences proved not accessible. Elaboration of glucosamine uronic acid disaccharide building blocks to trisaccharide modules by addition of either one additional glucosamine or uronic acid allowed for stereoselective access to oligosaccharides as demonstrated on the example of a hexasaccharide resembling the ATIII-binding sequence. Final deprotection and sulfation yielded the fully synthetic heparin oligosaccharides.     

Solid-Phase Enzymatic Synthesis of a Lewis a Trisaccharide Using an Acceptor Reversibly Bound to Sepharose

Abstract

The disaccharide 2-aminoethyl O-β-D-galactopyranosyl-(1→3)-2-acetamido-2-deoxy-β-D-glucopyranoside was reacted with thiobutyrolactone to give a disaccharide with a thiol group on the aglycone. This disaccharide was reacted with activated Thiopropyl Sepharose, which gave a disaccharide bound to Sepharose via a disulphide bond. Enzymatic fucosylation, using GDP-fucose and partially purified human milk fucosyltransferase, gave a trisaccharide in good yield, which was cleaved from Sepharose by treatment with mercaptoethanol or dithiothreitol.     

Synthesis of sulfonic acid analogues of the non-reducing end trisaccharide of the antithrombin binding domain of heparin

Three sulfonic acid trisaccharides related to the antithrombin-binding DEFGH domain of heparin were synthesised. Trisaccharides carrying the sulfonatomethyl moiety at position 2 or 6 were prepared in high yields by [DE+F] couplings using the same disaccharide uronate donor and the appropriate sulfonic acid acceptor, respectively. The trisaccharide with a 3-deoxy-3-sulfonatomethyl function could be obtained with high efficacy by a [D+EF] coupling where the carboxylic function of the EF uronate acceptor was created at a disaccharide level.     

Glycosylation of N-acetylglucosamine: imidate formation and unexpected conformation

[structure: see text] Rhamnosylation in mild conditions of a disaccharide containing N-acetylglucosamine afforded the imidate 6 while at higher temperature and concentration of promoter trisaccharide 7 was isolated. The kinetic imidate 6 was independently rearranged in 50% yield to the thermodynamic trisaccharide 7. Comparative NMR studies of 7 in CDCl(3) and DMSO-d(6) suggest the formation of a nonchair conformation in CDCl(3). The structure of 7 was confirmed through the independent synthesis of the N-acetylacetamido trisaccharide 11.     

The amide group in N-acetylglucosamine glycosyl acceptors affects glycosylation outcome

Glycosylation of a disaccharide containing N-acetylglucosamine with rhamnosyl and mannosyl trichloracetimidates under triethysilyl triflate catalysis led to the competitive formation of glycosyl imidates. While the rhamnosyl imidate could be rearranged to the thermodynamically favored trisaccharide, the mannosyl analogue was resistant to rearrangement. Glycosylation with perbenzylated thiorhamnosides activated with methyl triflate (MeOTf) gave the trisaccharide as well as the methyl imidate trisaccharide. The less reactive alpha-thioethyl donor led to a higher relative amount of methyl imidate trisaccharide to trisaccharide than the more reactive beta-thioglycoside. When using a more reactive thioethyl fucoside only the trisaccharide was obtained. Interestingly, the acceptor treated with MeOTf gave the N-methyl imidate that could be easily rhamnosylated and subsequently converted to the N-acetamido trisaccharide. This strategy to glycosylate O-4 of N-acetylglucosamine is under further investigation. Alternatively, bis-N-acetylation of the glucosamine prevented the formation of imidates and allowed the efficient synthesis of two Lewis A trisaccharide analogues.     

Synthesis and immunochemical studies on a Candida albicans cluster glycoconjugate vaccine

The immunoprotective beta-mannan of Candida albicans occurs as part of the cell wall phosphomannan N-linked glycoprotein. This macromolecule is composed of an extended alpha1,6 linked mannopyranan backbone containing alpha1,2 mannopyranan branches, to which beta1,2 mannopyranan epitopes are attached. The synthesis of beta1,2-mannan disaccharides clustered on a glucose core has been achieved as a way to imitate the multipoint display of beta-mannans in the native glycoprotein. The clustered epitopes were conjugated to tetanus toxoid and bovine serum albumin. Rabbits immunized with tetanus toxoid cluster glycoconjugate gave good antibody titres for the disaccharide cluster or simple trisaccharide epitope (coupled to BSA). The anti-sera also showed strong cross-reactivity with a Candida albicansbeta-mannan cell wall extract. These immunochemical results are compared with data obtained with non-cluster disaccharide and trisaccharide glycoconjugate antigens. The same conjugates gave substantially lower antibody levels when used to immunize mice.     

Synthesis and cholera toxin binding properties of multivalent GM1 mimics

Dendrimers based on the 3,5-di-(2-aminoethoxy)-benzoic acid branching unit were used to attach multiple copies of a GM1 mimic for inhibition of cholera toxin binding. Systems up to octavalent were synthesized along with relevant reference compounds that contained in one case the ligand in a monovalent format and in another case the scaffold but not the ligand. Using a surface plasmon resonance inhibition assay the prepared inhibitors showed good inhibition. While the monovalent GM1 mimic showed the expected inhibition in the 200 microM range the multivalent scaffolds led to increased binding. The tetravalent compound was shown to be 440-fold more potent than its monovalent counterpart. The octavalent analog, however, was the most potent compound as determined using an ELISA assay.     

First synthesis of 3′-deoxy Lewisx pentasaccharide

The total synthesis of 3′-deoxy Lewis^x pentasaccharide is reported. 4-O-Acetyl-2,6-di-O-benzoyl-3-deoxy-β-d-xylo-hexopyranosyl trichloroacetimidate was condensed with a diol of glucosamine to give a disaccharide, which was further fucosylated to a Lewis^x trisaccharide analogue. Glycosylation of a lactoside diol with this trisaccharide provided a pentasaccharide, which after deprotection, afforded the target pentasaccharide.     

N-连接的糖蛋白核心甘露五糖及其异构体的合成研究

以1,2-O-亚乙基-4,6-O-亚苄基-β-D-甘露糖(2)和2,3,4,6-四-O-苯甲酰基-α-D-甘露吡喃糖基三氯乙酰亚胺酯(3)为基本原料，经一些简单的化学转换和选择性的糖基化反应，得到了甘露核心五糖及其异构体。     

Structures of micelles formed by synthetic alkyl glycosides with unsaturated alkyl chains

Three new alkyl glycosides with similar molecular structures (oleyl and oleoyl alkyl chains and various head groups: disaccharide, trisaccharide and disaccharide with an additional amidoethoxy spacer) were synthesized and their supramolecular structure in aqueous solution was investigated. Small angle neutron scattering, surface tension measurement and the contact preparation method were applied to get molecular structure-property relationships. Although the chemical structures differ only in small details, their CMC values, lyotropic phase behaviour, surface area per surfactant molecule in the micelle and at the liquid-air interface, and the size and shape of the micelles are very different. We have found three different types of aggregates: spherical, cylindrical and polymer-like micelles in dilute solutions.     

一种木葡聚糖类寡糖的化学合成及生物活性

天然木葡聚糖类寡糖是一类对植物生长具有调节作用的寡糖, 本文以3个单糖组分为原料, 经5步合成了一种木葡聚糖三糖(1)(总产率15%), 以及该三糖的糖苷缀合物1a及其异构体1b. 利用糖基化立体选择性原则, 一步偶联反应同时得到所需的α,β连接产物, 整个合成路线高效简捷. 活性测试结果表明, 3种目标寡糖在1 mg/L浓度下, 对烟草的生长均显示出一定的促进作用, 表明所合成的3种寡糖有望发展成为植物生长促进剂.     

Synthesis and Preclinical Evaluation of QS-21 Variants Leading to Simplified Vaccine Adjuvants and Mechanistic Probes

QS-21 is a potent immunostimulatory saponin that is currently under clinical investigation as an adjuvant in various vaccines to treat infectious diseases, cancers, and cognitive disorders. Herein, we report the design, synthesis, and preclinical evaluation of simplified QS-21 congeners to define key structural features that are critical for adjuvant activity. Truncation of the linear tetrasaccharide domain revealed that a trisaccharide variant is equipotent to QS-21, while the corresponding disaccharide and monosaccharide congeners are more toxic and less potent, respectively. Modification of the acyl chain domain in the trisaccharide series revealed that a terminal carboxylic acid is well-tolerated while a terminal amine results in reduced adjuvant activity. Acylation of the terminal amine can, in some cases, restore adjuvant activity and enables the synthesis of fluorescently labeled QS-21 variants. Cellular studies with these probes revealed that, contrary to conventional wisdom, the most highly adjuvant active of these fluorescently labeled saponins does not simply associate with the plasma membrane, but rather is internalized by dendritic cells.     

Synthesis of GDP-5-thiosugars and their use as glycosyl donor substrates for glycosyltransferases

Two thiopyranoside analogues of GDP-sugars, GDP-5-thio-d-mannose (14) and GDP-5-thio-l-fucose (15), were synthesized. The syntheses included the phosphorylations of tetra-O-acetyl-5-thio-d-mannosyl bromide (4) and tri-O-benzoyl-l-fucosyl bromide (6) with silver dibenzyl phosphate, deprotection of the phosphate groups, and condensation of the deprotected phosphates with GMP-imidazolidate (13) in the presence of MgCl(2). These GDP-sugar analogues were found to be donor substrates for alpha(1,2)mannosyltransferase and alpha(1,3)fucosyltransferase, affording a 5-thiomannose-containing disaccharide (18) and a 5-thiofucose-containing trisaccharide (21), respectively. The conformation of the disaccharide analogue 18 was similar to that of its native counterpart by ROESY. These findings for GDP-5-thiosugars together with previous demonstrations of enzymatic transfer from UDP-5-thiosugars will allow the production of panels of oligosaccharide analogues with hydrolase-resistant properties.     

Synthesis of tri-, hexa-, and nonasaccharide subunits of the atypical O-antigen polysaccharide of the lipopolysaccharide from Danish Helicobacter pylori strains

Synthesis of trisaccharide repeating unit, -->3)-alpha-D-Rhap-(1-->2)-alpha-D-Manp3CMe-(1-->3)-alpha-L-Rha p-(1-->, and its dimeric hexa- and trimeric nonasaccharide subunits of the atypical O-antigen polysaccharide of the lipopolysaccharide from Danish H. pylori strains D1, D3, and D6 has been accomplished. Successful synthesis of the hexasaccharide and the nonasaccharide was possible by dimerization and trimerization of the suitably protected trisaccharide repeating unit, in which three monosaccharide moieties were arranged in a proper order by placing the sterically demanding 3-C-methyl-D-mannose moiety in between D- and L-rhamnoses. Key steps include the coupling of three monosaccharide moieties and dimerization and trimerization of the trisaccharide unit by glycosylations employing the 2'-carboxybenzyl glycoside method. Also presented is a method for the synthesis of the novel branched sugar, 3-C-methyl-D-mannose moiety by elaboration of its equatorial hydroxyl and axial methyl groups at C-3' in the disaccharide stage.     

Efficient synthesis of 3, 6-dideoxy-beta-D-arabino-hexopyranosyl-terminated LacdiNac glycan chains of the Trichinella spiralis parasite

The synthesis of a linear trisaccharide epitope of the Trichinella spiralis N-linked glycan, in a form amenable to glycoconjugate formation, is reported. The trisaccharide contains the synthetically challenging LacdiNAc [beta-GalpNAc(1-->4)-beta-GlcpNAc] element, as well as a terminal 3,6-dideoxy-beta-D-arabino-hexopyranose (tyvelose) residue. An orthogonal protection strategy is described, which permits the protection and manipulation of three amino groups present in the disaccharide beta-GalNAc(1-->4)-beta-GlcNAc and the tether used to prepare neoglycoconjugates. The beta-linked dideoxyhexose was generated in excellent yield by the introduction of the dideoxyhexose unit as a beta-D-ribo-hexopyranoside (paratose) followed by an oxidation-reduction sequence to generate the beta-D-arabino configuration in high diastereomeric excess. The required dideoxyhexose donor was synthesized in a series of high-yielding steps from glucose utilizing the p-methoxyphenyl glycoside.