Chemical and enzymatic synthesis of glycocluster having seven sialyl lewis X arrays using β-cyclodextrin as a key scaffold material

Antiviral Mechanism of Virucidal Sialic Acid Modified Cyclodextrin

We have reported that CD-6'SLN [6-sialyllactosamine (6'SLN)-modified β-cyclodextrin (CD)] can be a potential anti-influenza drug because it irreversibly deactivates virions. Indeed, in vivo, CD-6'SLN improved mice survival in an H1N1 infection model even when administered 24 h post-infection. Although CD-6'SLN was designed to target the viral envelope protein hemagglutinin (HA), a natural receptor of 6'SLN, it remains unclear whether other targets exist. In this study, we confirm that CD-6'SLN inhibits the influenza virus through an extracellular mechanism by interacting with HA, but not with neuraminidase (NA), despite the latter also having a binding pocket for the sialyl group. We find that CD-6'SLN interacts with the viral envelope as it elicits the release of a fluorophore embedded in the membrane. Two similar compounds were designed to test separately the effect of 6'SLN and of the undecyl moiety that links the CD to 6'SLN. Neither showed any interaction with the membrane nor the irreversible viral inhibition (virucidal), confirming that both components are essential to membrane interaction and virucidal action. Unlike similar antiviral cyclodextrins developed against other viruses, CD-6'SLN was not able to decapsulate viral RNA. Our findings support that combining viral protein-specific epitopes with hydrophobic linkers provides a strategy for developing antiviral drugs with a virucidal mechanism.

Glyconanomaterials for biosensing applications

Nanomaterials constitute a class of structures that have unique physiochemical properties and are excellent scaffolds for presenting carbohydrates, important biomolecules that mediate a wide variety of important biological events. The fabrication of carbohydrate-presenting nanomaterials, glyconanomaterials, is of high interest and utility, combining the features of nanoscale objects with biomolecular recognition. The structures can also produce strong multivalent effects, where the nanomaterial scaffold greatly enhances the relatively weak affinities of single carbohydrate ligands to the corresponding receptors, and effectively amplifies the carbohydrate-mediated interactions. Glyconanomaterials are thus an appealing platform for biosensing applications. In this review, we discuss the chemistry for conjugation of carbohydrates to nanomaterials, summarize strategies, and tabulate examples of applying glyconanomaterials in in vitro and in vivo sensing applications of proteins, microbes, and cells. The limitations and future perspectives of these emerging glyconanomaterials sensing systems are furthermore discussed.

Cyclodextrin-based multivalent glycodisplays: covalent and supramolecular conjugates to assess carbohydrate-protein interactions

Covalent attachment of biorecognizable sugar ligands in several copies at precise positions of cyclomaltooligosaccharide (cyclodextrin, CD) macrocycles has proven to be an extremely flexible strategy to build multivalent conjugates. The commercial availability of the native CDs in three different sizes, their axial symmetry and the possibility of position- and face-selective functionalization allow a strict control of the valency and spatial orientation of the recognition motifs (glycotopes) in low, medium, high and hyperbranched glycoclusters, including glycodendrimer-CD hybrids. "Click-type" ligation chemistries, including copper(i)-catalyzed azide-alkyne cycloaddition (CuAAC), thiol-ene coupling or thiourea-forming reactions, have been implemented to warrant full homogeneity of the adducts. The incorporation of different glycotopes to investigate multivalent interactions in heterogeneous environments has also been accomplished. Not surprisingly, multivalent CD conjugates have been, and continue to be, major actors in studies directed at deciphering the structural features ruling carbohydrate recognition events. Nanometric glycoassemblies endowed with the capability of adapting the inter-saccharide distances and orientations in the presence of a receptor partner or capable of mimicking the fluidity of biological membranes have been conceived by multitopic inclusion complex formation, rotaxanation or self-assembling. Applications in the fields of sensors, site-specific drug and gene delivery or protein stabilization attest for the maturity of the field.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for the period 2005-2006

This review is the fourth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2006. The review covers fundamental studies, fragmentation of carbohydrate ions, method developments, and applications of the technique to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, glycated proteins, glycolipids from bacteria, glycosides, and various other natural products. There is a short section on the use of MALDI-TOF mass spectrometry for the study of enzymes involved in glycan processing, a section on industrial processes, particularly the development of biopharmaceuticals and a section on the use of MALDI-MS to monitor products of chemical synthesis of carbohydrates. Large carbohydrate-protein complexes and glycodendrimers are highlighted in this final section.

Inhibition binding studies of glycodendrimer-lectin interactions using surface plasmon resonance

Understanding protein-carbohydrate interactions is essential for elucidating biological pathways and cellular mechanisms but is often difficult due to the prevalence of multivalent interactions. Here, we evaluate the multivalent glycodendrimer framework as a means to describe the inhibition potency of multivalent mannose-functionalized dendrimers using surface plasmon resonance (SPR). Using highly robust, mannose-functionalized dithiol self-assembled monolayers on gold surfaces, we found that glycodendrimers were efficient inhibitors of protein-carbohydrate interactions. IC(50) values ranging from 260 nM to 13 nM were obtained for mannose-functionalized dendrimers with Concanavalin A.

Design and creativity in synthesis of multivalent neoglycoconjugates

From the authors' opinion, this chapter constitutes a modest extension of the seminal and inspiring contribution of Stowell and Lee on neoglycoconjugates published in this series [C. P. Stowell and Y. C. Lee, Adv. Carbohydr. Chem. Biochem., 37 (1980) 225-281]. The outstanding progresses achieved since then in the field of the "glycoside cluster effect" has witnessed considerable creativity in the design and synthetic strategies toward a vast array of novel carbohydrate structures and reflects the dynamic activity in the field even since the recent chapter by the Nicotra group in this series [F. Nicotra, L. Cipolla, F. Peri, B. La Ferla, and C. Radaelli, Adv. Carbohydr. Chem. Biochem., 61 (2007) 353-398]. Beyond the more classical neoglycoproteins and glycopolymers (not covered in this work) a wide range of unprecedented and often artistically beautiful multivalent and monodisperse nanostructures, termed glycodendrimers for the first time in 1993, has been created. This chapter briefly surveys the concept of multivalency involved in carbohydrate-protein interactions. The topic is also discussed in regard to recent steps undertaken in glycobiology toward identification of lead candidates using microarrays and modern analytical tools. A systematic description of glycocluster and glycodendrimer synthesis follows, starting from the simplest architectures and ending in the most complex ones. Presentation of multivalent glycostructures of intermediate size and comprising, calix[n]arene, porphyrin, cyclodextrin, peptide, and carbohydrate scaffolds, has also been intercalated to better appreciate the growing synthetic complexity involved. A subsection describing novel all-carbon-based glycoconjugates such as fullerenes and carbon nanotubes is inserted, followed by a promising strategy involving dendrons self-assembling around metal chelates. The chapter then ends with those glycodendrimers that have been prepared using commercially available dendrimers possessing varied functionalities, or systematically synthesized using either divergent or convergent strategies.

Fucosylated Pentaerythrityl Phosphodiester Oligomers (PePOs): Automated Synthesis of DNA-Based Glycoclusters and Binding to Pseudomonas aeruginosa Lectin (PA-IIL)

The synthesis of propargylated pentaerythrityl phosphodiester oligomers (PePOs) was achieved using a DNA synthesizer with a bis-propargylated pentaerythritol-based phosphoramidite. An azido fucose derivative was reacted under "click" chemistry conditions activated by microwaves to construct a series of glycosylated PePOs bearing 4, 6, 8, and 10 L-fucose residues. Binding to the fucose-specific bacterial lectin (PA-IIL) was determined for the fucosylated PePOs through an enzyme-linked lectin amplification competition assay. The IC50 values measured are 10-20 times better than for monovalent l-fucose and denotate for a "macromolecular" effect rather than a "cluster" effect.

Spacer-separated sialyl LewisX cyclopeptide conjugates as potential E-selectin ligands

Completely protected sialyl LewisX azide was synthesized from a neolactosamine azide precursor carrying a 3-O-allyloxycarbonyl group as the temporary protecting group. After its Pd(0)-catalyzed deprotection and stereoselective alpha-fucosylation, the obtained LewisX azide was subjected to O-deacetylation in the galactose unit and subsequent regio- and stereoselective sialylation. Reduction of the anomeric azido group afforded the sialyl LewisX amine building block. Two molecules of this tetrasaccharide ligand were conjugated to a preformed cyclooctapeptide containing two equidistant l-asparagine units equipped with carboxy-terminated tetraethyleneglycol side chains to give, after deprotection, the target glycopeptide conjugate. Preliminary biological evaluation of the synthesized bivalent sialyl LewisX cyclopeptide conjugate showed only slightly enhanced inhibition of E-selectin binding in spite of the given flexibility of the two linked saccharide determinants.

Survey of the year 2005 commercial optical biosensor literature

We identified 1113 articles (103 reviews, 1010 primary research articles) published in 2005 that describe experiments performed using commercially available optical biosensors. While this number of publications is impressive, we find that the quality of the biosensor work in these articles is often pretty poor. It is a little disappointing that there appears to be only a small set of researchers who know how to properly perform, analyze, and present biosensor data. To help focus the field, we spotlight work published by 10 research groups that exemplify the quality of data one should expect to see from a biosensor experiment. Also, in an effort to raise awareness of the common problems in the biosensor field, we provide side-by-side examples of good and bad data sets from the 2005 literature.