Automated synthesis of oligosaccharides as a basis for drug discovery.

Carbohydrates present both potential and problems - their biological relevance has been recognized, but problems in procuring sugars rendered them a difficult class of compounds to handle in drug discovery efforts. The development of the first automated solid-phase oligosaccharide synthesizer and other methods to assemble defined oligosaccharides rapidly has fundamentally altered this situation. This review describes how quick access to oligosaccharides has not only contributed to biological, biochemical and biophysical investigations, but also to drug discovery.

Chemical approaches to define the structure-activity relationship of heparin-like glycosaminoglycans.

Heparin, the drug of choice for the prevention and treatment of thromboembolic disorders, has been shown to interact with many proteins. Despite its widespread medical use, little is known about the precise sequences that interact with specific proteins. The minimum heparin binding sequence for FGF1 and FGF2 necessary to promote signaling was investigated.

Efficient installation of beta-mannosides using a dehydrative coupling strategy.

[reaction: see text]. A new coupling procedure for the construction of the challenging beta-mannosidic bond is described. Dehydrative mannosylation using 4,6-O-benzylidene mannopyranoses allows for the formation of beta-mannosides in excellent yield.

Total syntheses of fully lipidated glycosylphosphatidylinositol anchors of Toxoplasma gondii.

Modular syntheses of the glycosylphosphatidylinositol anchors of Toxoplasma gondii using a highly convergent strategy are reported.

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.

Convergent synthesis of a fully lipidated glycosylphosphatidylinositol anchor of Plasmodium falciparum.

A highly convergent strategy for the synthesis of fully lipidated GPI anchors of malarial origin is reported. This strategy utilized three orthogonal protecting groups, which can be chemoselectively deprotected and functionalized in the late stage of the synthesis. Rapid access to the target GPIs in a highly efficient manner in sufficient quantities for the biological studies has been achieved.

Carbohydrates as the next frontier in pharmaceutical research.

Synthetic carbohydrates and glycoconjugates are used to study their roles in biological important processes such as inflammation, cell-cell recognition, immunological response, metastasis, and fertilization. The development of an automated oligosaccharide synthesizer greatly accelerates the assembly of complex, naturally occurring carbohydrates as well as chemically modified oligosaccharide structures and promises to have major impact on the field of glycobiology. Tools such as microarrays, surface plasmon resonance spectroscopy, and fluorescent carbohydrate conjugates to map interactions of carbohydrates in biological systems are presented.

Assembly of a series of malarial glycosylphosphatidylinositol anchor oligosaccharides.

We report an efficient and convergent synthesis of a series of oligosaccharides comprised of the malaria GPI glycan (2a), a promising anti-malaria vaccine candidate currently in preclinical trials and several related oligosaccharide sequences (3-8) that are possible biosynthetic precursors of the malarial GPI. A flexible synthetic strategy is disclosed that relies on a late-stage coupling between oligomannosides of varying length and pseudo-disaccharide glycosyl acceptor 11 to readily access various malarial GPI structures. Phosphorylation was accomplished by mild and efficient H-phosphonate chemistry before the final deprotection was carried out by using sodium in ammonia.

Microreactor-based reaction optimization in organic chemistry--glycosylation as a challenge.

Glycosylation reactions are performed rapidly over a wide range of conditions as an example of microreactor-based method optimization and process development in organic chemistry.

The use of carbohydrate microarrays to study carbohydrate-cell interactions and to detect pathogens.

The use of carbohydrate microarrays to investigate the carbohydrate binding specificities of bacteria, to detect pathogens, and to screen antiadhesion therapeutics is reported. This system is ideal for whole-cell applications because microarrays present carbohydrate ligands in a manner that mimics interactions at cell-cell interfaces. Other advantages include assay miniaturization, since minimal amounts (approximately picomoles) of a ligand are required to observe binding, and high throughput, since thousands of compounds can be placed on an array and analyzed in parallel.

Carbohydrate diversity: synthesis of glycoconjugates and complex carbohydrates.

The fundamental role of glycoconjugates in many biological processes is now well appreciated and has intensified the development of innovative and improved synthetic strategies. All areas of synthetic methodology have seen major advances and many complex, highly branched carbohydrates and glycoproteins have been prepared using solution- and/or solid-phase approaches. The development of an automated oligosaccharide synthesizer provides rapid access to biologically relevant compounds.

Detection of bacteria with carbohydrate-functionalized fluorescent polymers.

Many pathogens that infect humans use cell surface carbohydrates as receptors to facilitate cell-cell adhesion. The hallmark of these interactions is their multivalency, or the simultaneous occurrence of multiple interactions. We have used a carbohydrate-functionalized fluorescent polymer, which displays many carbohydrate ligands on a single polymer chain, to allow for multivalent detection of pathogens.

Tools for glycomics: mapping interactions of carbohydrates in biological systems.

The emerging field of glycomics has been challenged by difficulties associated with studying complex carbohydrates and glycoconjugates. Advances in the development of synthetic tools for glycobiology are poised to overcome some of these challenges and accelerate progress towards our understanding of the roles of carbohydrates in biology. Carbohydrate microarrays, fluorescent neoglycoconjugate probes, and aminoglycoside antibiotic microarrays are among the many new tools becoming available to glycobiologists.

A Suzuki-Miyaura coupling mediated deprotection as key to the synthesis of a fully lipidated malarial GPI disaccharide.

Ligandless palladium-catalyzed Suzuki-Miyaura coupling converted an inert p-bromobenzyl ether to a DDQ-labile p-(3,4-dimethoxyphenyl) benzyl ether in the presence of azide functionality and this strategy serves as a key step for the convergent synthesis of a fully lipidated malaria GPI disaccharide.

A convergent, versatile route to two synthetic conjugate anti-toxin malaria vaccines.

The synthesis of two glycosylphosphatidyl inositol (GPI) glycans that constitute the malaria toxin and promising anti-toxin vaccine constructs using a scalable route is described.

Aminoglycoside microarrays to explore interactions of antibiotics with RNAs and proteins.

RNA is an important target for drug discovery efforts. Several clinically used aminoglycoside antibiotics bind to bacterial rRNA and inhibit protein synthesis. Aminoglycosides, however, are losing efficacy due to their inherent toxicity and the increase in antibiotic resistance.

Oligosaccharide and glycoprotein microarrays as tools in HIV glycobiology; glycan-dependent gp120/protein interactions.

Defining HIV envelope glycoprotein interactions with host factors or binding partners advances our understanding of the infectious process and provides a basis for the design of vaccines and agents that interfere with HIV entry. Here we employ carbohydrate and glycoprotein microarrays to analyze glycan-dependent gp120-protein interactions. In concert with new linking chemistries and synthetic methods, the carbohydrate arrays combine the advantages of microarray technology with the flexibility and precision afforded by organic synthesis.

A stereochemical surprise at the late stage of the synthesis of fully N-differentiated heparin oligosaccharides containing amino, acetamido, and N-sulfonate groups.

The glucosamine residues in heparin-like glycosaminoglycans have been found to exist as amines, acetamides, and N-sulfonates. To develop a completely general, modular synthesis of heparin, three degrees of orthogonal nitrogen protection are required. Reported herein is a strategy for the synthesis of fully N-differentiated heparin oligosaccharides in the context of target octasaccharide 1, which contains an N-acetate, N-sulfonates, and a free amine.

Solid-phase synthesis and 1H and 13C high-resolution magic angle spinning NMR of 13C-labeled resin-bound saccharides.

We show how high-resolution magic angle-spinning NMR spectroscopy can be used to characterize 13C-labeled saccharides that have been prepared using solid-phase synthesis techniques while they are still bound to a solid-support resin. With the use of 13C-labeled glucose as the starting material, we have successfully synthesized mono-, di- and trisaccharides with uniform 13C labeling of the saccharide rings. Using these materials, we have been able to assign the 13C and 1H spectra and to characterize various impurities on the resin beads.

Automated synthesis of a protected N-linked glycoprotein core pentasaccharide.

[structure: see text] Described is the first automated solid-phase synthesis of the core N-linked pentasaccharide, common to all N-linked glycoproteins via stepwise assembly from mono- and disaccharide building blocks. The challenging beta-mannosidic linkage was incorporated by the inclusion of a disaccharide trichloroacetimidate. This automated synthesis provides rapid access to an oligosaccharide common to an entire class of glycoconjugates.