Monosaccharide Building Blocks Research Articles

An Improved Synthetic Route to the Potent Angiogenesis Inhibitor Benzyl Manα(1→3)-Manα(1→3)-Manα(1→3)-Manα(1→2)-Man Hexadecasulfate

An improved synthetic route to α(1→3)/α(1→2)-linked mannooligosaccharides has been developed and applied to a more efficient preparation of the potent anti-angiogenic sulfated pentasaccharide, benzyl Manα(1→3)-Manα(1→3)-Manα(1→3)-Manα(1→2)-Man hexadecasulfate, using only two monosaccharide building blocks. Of particular note are improvements in the preparation of both building blocks and a simpler, final deprotection strategy. The route also provides common intermediates for the introduction of aglycones other than benzyl, either at the building block stage or after oligosaccharide assembly. The anti-angiogenic activity of the synthesized target compound was confirmed via the rat aortic assay.

2-Nitroglycals as Powerful Glycosyl Donors: Application in the Synthesis of Biologically Important Molecules

[Reaction: see text]. The biological significance of oligosaccharides and glycoconjugates is profound and wide-ranging. For example, the mucins have attracted attention because of their role in fundamental cellular processes such as fertilization, parasitic infection, inflammation, immune defense, cell growth, and cell-cell adhesion. Increased expression of mucins is implicated in malignant transformation of cells. Antifreeze glycoproteins also are of interest because they are important for the survival of many marine teleost fishes that live in polar and subpolar waters. The synthesis of glycoconjugates requires methods for glycoside bond formation, the most difficult aspect of which is the assembly of monosaccharide building blocks. This Account discusses a valuable addition to the repertoire of methods for glycoconjugate synthesis: an approach that involves 2-nitroglycal concatenation. For a long time, methods for glycosylation via glycosyl donor generation required either an anomeric oxygen exchange reaction or anomeric oxygen retention. In the case of an anomeric oxygen exchange reaction, activation of the glycosyl donors demands a promoter in at least equimolar amounts. However, anomeric oxygen retention, such as base-catalyzed formation of O-glycosyl trichloroacetimidates, can be activated by catalytic amounts of acid or Lewis acid. Alternatively, glycals, which are readily available from sugars, can be an attractive starting material for glycoside bond formation. Their nucleophilic character at C-2 permits reactions with oxygen, nitrogen, and sulfur electrophiles that under high substrate stereocontrol generally lead to three-membered rings; ring opening under acid catalysis furnishes the corresponding glycosides, whichdepending on the electrophile Xare also employed for 2-deoxyglycoside synthesis. Glycals also can be transformed into derivatives that have at C-2 an electron-withdrawing group and are amenable to Michael-type addition. A good example are 2-nitroglycals. In this case, glycoside bond formation is achieved under base catalysis and leads to 2-deoxy-2-nitroglycosides. These intermediates are readily converted into 2-amino-2-deoxyglycosides, which are constituents of almost all glycoconjugates. This 2-nitroglycal concatenation has been extensively investigated with 2-nitrogalactal derivatives. When alcohols are used as nucleophiles and strong bases used as catalysts, the result is primarily or exclusively the alpha-galacto-configured adducts. Some studies show that weaker bases may lead to preferential formation of the beta-galacto-configured products instead. The reaction was very successfully extended to other nucleophiles and also to other 2-nitroglycals that undergo base-catalyzed stereoselective Michael-type additions. Thus, 2-nitroglycals are versatile synthons in glycoconjugate and natural-products synthesis, and it is foreseeable that many more applications will be based on these readily available and highly functionalized skeletons.

Sequential One-Pot Glycosidations Catalytically Promoted: Unprecedented Strategy in Oligosaccharide Synthesis for the Straightforward Assemblage of the Antitumor PI-88 Pentasaccharide

The pentasaccharide sequence of the most active components of the antitumor drug PI-88, currently in phase II clinical trial, has been rapidly assembled in high overall yield and in only three steps starting from three monosaccharide building blocks. The procedure takes advantage of the first reported strategy of sequential one-pot glycosidations conducted exclusively under catalytic activation. In addition, the procedure relies only on shelf-stable and mild promoters such as Yb(OTf)(3) and Bi(OTf)(3).

Improved Synthesis of the Tetrasaccharide Repeat Unit of the O-Antigen Polysaccharide from Escherichia coli O77

The efficient synthesis of a tetrasaccharide, the suitably protected form of the repeat unit, →2)-α-D-Manp-(1→2)-β-D-Manp-(1→3)-α -D-GlcpNAc -(1→6)-α -D-Manp-(1→, of the 0-antigen polysaccharide of the lipopolysaccharide from E. coli 077 has been accomplished. Glycosylation reactions for the coupling of four monosaccharide building blocks of the tetrasaccharide were carried out employing the CB glycoside method, the mannosyl 4-pentenoate/PhSeOTf method, and the glycosyl trichloroacetimidate method with complete stereoselectivities in excellent yields.

Efficient Chemical Synthesis of Sialic Acid Related Oligosaccharides

A very efficient strategy for the chemical synthesis of the sialyl Lewis X tetrasaccharide is reported. Starting from four simple monosaccharide building blocks, sialyl Lewis X was obtained in seven steps. By using similar strategy, sialyl LacNAc and sulfated sialyl LacNAc trisaccharides were also synthesized.

Solution Syntheses of Protected Type II Lewis Blood Group Oligosaccharides: Study for Automated Synthesis.

Glycosyl phosphate and trichloroacetimidate monosaccharide building blocks were used in a stepwise solution-phase synthesis of three Lewis blood group oligosaccharides. The syntheses were conducted to establish general routes for the automated assembly of the oligosaccharide portion of biologically important glycolipids. The H-type II pentasaccharide, Lex pentasaccharide, and Ley hexasaccharide were prepared in high yield. These syntheses served to evaluate the utility and limitations of the 2-(azidomethyl)benzoate ester (AZMB) for the construction of complex carbohydrates. Development of a glucosamine building block containing a N-trichloroacetamide group to mask the C2 amine improved coupling yields and was key for completion of the Lex and Ley structures.

Solution Syntheses of Protected Type II Lewis Blood Group Oligosaccharides: Study for Automated Synthesis

Glycosyl phosphate and trichloroacetimidate monosaccharide building blocks were used in a stepwise solution-phase synthesis of three Lewis blood group oligosaccharides. The syntheses were conducted to establish general routes for the automated assembly of the oligosaccharide portion of biologically important glycolipids. The H-type II pentasaccharide, Le(x) pentasaccharide, and Le(y) hexasaccharide were prepared in high yield. These syntheses served to evaluate the utility and limitations of the 2-(azidomethyl)benzoate ester (AZMB) for the construction of complex carbohydrates. Development of a glucosamine building block containing a N-trichloroacetamide group to mask the C2 amine improved coupling yields and was key for completion of the Le(x) and Le(y) structures.

Development of specific inhibitors for heparin-binding proteins based on the cobra cardiotoxin structure: an effective synthetic strategy for rationally modified heparin-like disaccharides and a trisaccharide

Recently, a new heparin disaccharide-binding site on the convex side of cobra cardiotoxin (CTX) was identified by NMR spectroscopy and molecular modeling. To further characterize this site two heparin-like disaccharides were synthesized for binding studies with CTX, and a trisaccharide was synthesized for testing the sequence of the disaccharide binding to CTX. Thus six differentially protected monosaccharide building blocks (three l-iduronic acids and three d-glucosamines) were prepared. These include a l-iduronic acid elongation building block namely methyl 2- O-acetyl-4- O-levulinoyl-3- O-pivaloyl-α- l-idopyranosyluronate trichloroacetimidate for which a single-crystal X-ray structure was determined to have M r = 576.79, a = 9.3098(11) Å α = 90°, b = 10.3967(12) Å β = 90°, c = 28.026(3) Å γ = 90°, V = 2712.7(6) Å 3, P2 12 12 1, Z = 4, μ = 0.71073 Å, and R = 0.0378 for 7586 observed reflections. It shows that the molecular structure of the donor is in the 1 C 4 conformation with significant 1,3-diaxial interactions between O-1 and O-3 as well as O-2 and O-4. The disaccharides and trisaccharide vary in the degree and position of O- and N-sulfation. The pivaloyl group was used as permanent protecting group of hydroxyl. The levulinoyl group was used as the temporary protecting group to protect the hydroxyl for elongation.

Studies on the Synthesis of Trisaccharide Analogues of the Antibiotic Moenomycin A

AbstractA new approach for the synthesis of moenomycin trisaccharide analogues is reported in which three monosaccharide building blocks are used and allows the introduction of different substituents at the 6‐position of unit E (Scheme 2). Furthermore, a new procedure for the introduction and manipulation of unit F is described (Scheme 3).

New set of orthogonal protecting groups for the modular synthesis of heparan sulfate fragments.

Six strategically chosen monosaccharide building blocks, which are protected by a novel set of four orthogonal protecting groups (Lev, Fmoc, TBDPS, and All), can be employed for the efficient synthesis of the 20 disaccharide moieties found in heparan sulfate. The properly protected disaccharide building blocks can be converted into glycosyl donors and acceptors, which can be used for the modular synthesis of a wide range of well-defined oligosaccharides that differ in sulfation pattern. [structure: see text]

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 α-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.

Linear Synthesis of the Tumor‐Associated Carbohydrate Antigens Globo‐H, SSEA‐3, and Gb3.

The tumor-associated carbohydrate antigens Globo-H, SSEA-3, and Gb3 were synthesized in a linear fashion using glycosyl phosphate monosaccharide building blocks. All of the building blocks were prepared from readily available common precursors. The difficult α-(1→4-cis)-galactosidic linkage was installed using a galactosyl phosphate donor with high selectivity. Introduction of the β-galactosamine unit required the screening a variety of amine protecting groups to ensure good donor reactivity and protecting group compatibility. An N-trichloroacetyl-protected galactosamine donor performed best for the installation of the β-glycosidic linkage. Conversion of the trichloroacetyl group to the N-acetyl group was achieved under mild conditions, fully compatible with the presence of multiple glycosidic bonds. This synthetic strategy is expected to be amenable to the synthesis of the globo-series of tumor antigens on solid-support.

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.

Linear synthesis of the tumor-associated carbohydrate antigens Globo-H, SSEA-3, and Gb3.

The tumor-associated carbohydrate antigens Globo-H, SSEA-3, and Gb3 were synthesized in a linear fashion using glycosyl phosphate monosaccharide building blocks. All of the building blocks were prepared from readily available common precursors. The difficult alpha-(1-->4-cis)-galactosidic linkage was installed using a galactosyl phosphate donor with high selectivity. Introduction of the beta-galactosamine unit required the screening a variety of amine protecting groups to ensure good donor reactivity and protecting group compatibility. An N-trichloroacetyl-protected galactosamine donor performed best for the installation of the beta-glycosidic linkage. Conversion of the trichloroacetyl group to the N-acetyl group was achieved under mild conditions, fully compatible with the presence of multiple glycosidic bonds. This synthetic strategy is expected to be amenable to the synthesis of the globo-series of tumor antigens on solid-support.

A Linear Synthesis of Branched High-Mannose Oligosaccharides from the HIV-1 Viral Surface Envelope Glycoprotein gp120

Described is a linear solution-phase synthesis of the HIV-1 viral surface envelope glycoprotein gp120 high-mannose nonasaccharide pentyl glycoside. Envisioning the automated solid-phase assembly of complex carbohydrates, the synthesis of the nonasaccharide and the related tri- and hexamannosides demonstrates the facile assembly of highly branched structures in a stepwise fashion incorporating monosaccharide building blocks. A differentially protected core trisaccharide was prepared and further elongated in two high-yielding tri-mannosylations to furnish the triantennary structure. The tri-, hexa-, and nonamannoside n-pentyl glycosides obtained via the described synthesis are currently being used for detailed study of the carbohydrate protein interactions responsible for binding of the anti-HIV protein cyanovirin-N to the glycoprotein gp120. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Synthesis of pseudo-oligosaccharides by a sequence of yne-ene cross metathesis and Diels–Alder reaction

Various pseudo oligosaccharides were prepared by a combination of selective yne-ene cross metathesis and Diels–Alder reaction from readily available monosaccharide building blocks.

Staining particulate organic matter with DTAF--a fluorescence dye for carbohydrates and protein:a new approach and application of a 2D image analysis system

Aggregates consist in many cases of microorganisms attached to an organic matrix. Several attempts have been made to visualise the mucoid components of the matrix by staining (e.g. alcian blue for carbohydrates and coomassie brilliant blue for proteins). Modern equipment, such as epfluorescence microscopes, flow cytometers and confocal laser scanning n?icroscopes, requires or works best with fluorescently marked objects. Therefore, there is a great need for a fluorescent dye to visualise polysaccharides associated with aggregates. Like proteins, polysaccharides are very heterogeneous in their 3-dunensional structure. Depending on the types of interglycosidic bonds and the orders of monosaccharide building blocks, various conformations are possible (i.e. helices or molecule layers). Moreover, saccharides are very hard to modify covalently in water at natural pH levels. To date, the only available fluorescence marker is 5-(4,6-dichlorotriazinyl)aminofluorescein (DTAF), which binds covalently to polysaccharides at room temperature when the pH is above 9 This paper compares the results of staining particulate organic matter (POM) with DTAF with the results of staining with the DNA-specific stain propidium iodide, which has been recently introduced to visualise detritus. Results are related to other POM properties, e.g. particle volume measured by coultere Counter and particulate organic carbon (POC). When plankton and floccular sediment layer samples were stained with DTAF, the total particle volume was, in 13 out of 17 samples, 11 to 393% greater than that revealed by propidium iodide. The mucoid matrix of large particles (>50 pm charneter) stained well with DTAF, whereas this material was only weakly detected w t h propidium iodide. In contrast, very small particles such as bacteria were seen better with propidium iohde. The total parbcle volume of a DTAF-stained sample calculated from 2-dimensional image analysis data correlated significantly with POC, total particulate polysaccharides, Coultera-counter-derived total particle volume, and light-microscope-derived summed volumes of bacteria, phytoplankton and protozooplankton. The total biovolumes contributed on average 62% of the Coultera Counter volume and 45% of propidium-iodide-stainable and 50% of DTAF-stainable volume in plankton samples from the Kirr Bucht and 58,59 and 61 % from the Rassower Strom, respectively. The remaining volume must be interpreted as the volume of amorphous detritus and, particularly in the case of the fluorescently stained particles, also as amorphous organic material.

Analysis of protein glycosylation by mass spectrometry.

There is a growing pharmaceutical market for protein-based drugs for use in therapy and diagnosis. The rapid developments in molecular and cell biology have resulted in production of expression systems for manufacturing of recombinant proteins and monoclonal antibodies. These proteins are glycosylated when expressed in cell systems with glycosylation ability. For glycoproteins intended for therapeutic administration it is important to have knowledge about the structure of the carbohydrate side chains to avoid cell systems that produce structures, which in humans can cause undesired reactions, e.g., immunological and unfavorable serum clearance rate. Structural analysis of glycoprotein oligosaccharides requires sophisticated instruments like mass spectrometers and nuclear magnetic resonance spectrometers. However, before the structural analysis can be conducted, the carbohydrate chains have to be released from the protein and purified to homogeneity, and this is often the most time-consuming step. Mass spectrometry has played and still plays an important role in analysis of protein glycosylation. The superior sensitivity compared to other spectroscopic methods is its main asset. Structural analysis of carbohydrates faces several problems, however, due to the chemical nature of the constituent monosaccharide residues. For oligosaccharides or glycoconjugates, the structural information from mass spectrometry is essentially limited to monosaccharide sequence, molecular weight, an only in exceptional cases glycosidic linkage positions can be obtained. In order to completely establish an oligosaccharide structure, several other structural parameters have to be determined, e.g., linkage positions, anomeric configuration and identification of the monosaccharide building blocks. One way to address some of these problems is to work on chemical pretreatment of the glycoconjugate, to specifically modify the carbohydrate chain. In order to introduce specific modifications, we have used periodate oxidation and trifluoroacetolysis with the objective of determining glycosidic linkage positions by mass spectrometry.

Synthesis of di- to penta-saccharides related to the O-specific polysaccharide of Shigella dysenteriae type 1, and their nuclear magnetic resonance study

The syntheses of oligosaccharide fragments of the O-specific polysaccharide of the lipopolysaccharide of Shigella dysenteriae type 1 are described, including disaccharides methyl O-α- d-mannopyranosyl-(1→2)-α- d-galactopyranoside ( 1), and methyl O-(2-deoxy-2-propionamido-α- d-glucopyranosyl)-(1→3)-α- l-rhamnopyranoside ( 2), trisaccharide methyl O-α- d-galactopyranosyl-(1→3)- O-(2-acetamido-2-deoxy-α- d-glucopyranosyl)-(1→3)-α- l-rhamnopyranoside ( 3), tetrasaccharide methyl O-α- l-rhamnopyranosyl-(1→2)- O-α- d-galactopyranosyl-(1→3)- O-(2-acetamido-2-deoxy-α- d-glucopyranosyl)-(1→3)-α- l-rhamno-pyranoside ( 4), and pentasaccharide methyl O-α- l-rhamnopyranosyl-(1→3)- O-α- l-rhamnopyranosyl-(1→2)- O-α- d-galactopyranosyl-(1→3)- O-(2-acetamido-2-deoxy-α- d-glucopyranosyl)-(1→3)-α- l-rhamnopyranoside ( 5). The following monosaccharide building blocks were used as starting compounds: methyl 6- O- tert-butyldiphenylsilyl-3,4- O-isopropylidene-α- d-galactopyranoside ( 8), methyl 3,4,6-tri- O-benzyl-2- O-(4-methoxybenzyl)-1-thio-β- d-galactopyranoside ( 11), methyl 3,4,6-tri- O-acetyl-2-azido-2-deoxy-1-thio-α- d-glucopyranoside ( 16), methyl 2-azido-4,6- O-benzylidene-2-deoxy-1-thio-α- d-glucopyranoside ( 18), methyl 2,4-di- O-benzyl-α- l-rhamnopyranoside ( 21), methyl 2,3,4-tri- O-benzoyl-1-thio-α- l-rhamnopyranoside ( 22), 2,3,4-tri- O-benzoyl-α- l-rhamnopyranosyl bromide ( 23), and methyl 4- O-benzyl-α- l-rhamnopyranoside ( 24). Nuclear magnetic resonance data indicate that oligosaccharides 4 and 5 partially mimic the conformation of the O-specific polysaccharide of S. dys. type 1.