Specificity of C-glycoside complexation by mannose/glucose specific lectins

Glucose-Binding Dioclea bicolor Lectin (DBL): Purification, Characterization, Structural Analysis, and Antibacterial Properties

In this study, we purified a lectin isolated from the seeds of Dioclea bicolor (DBL) via affinity purification. Electrophoresis analysis revealed that DBL had three bands, α, β, and γ chains, with molecular masses of approximately 29, 14, and 12 kDa, respectively. Gel filtration chromatography revealed that the native form of DBL had a molecular mass of approximately 100 kDa, indicating that it is a tetramer. Interestingly, DBL-induced hemagglutination was inhibited by several glucosides, mannosides, ampicillin, and tetracycline with minimum inhibitory concentration (MIC) values of 1.56-50 mM. Analysis of the complete amino acid sequence of DBL revealed the presence of 237 amino acids with high similarity to other Diocleinae lectins. Circular dichroism showed the prominent β-sheet secondary structure of DBL. Furthermore, DBL structure prediction revealed a Discrete Optimized Protein Energy (DOPE) score of -26,642.69141/Normalized DOPE score of -1.84041. The DBL monomer was found to consist a β-sandwich based on its 3D structure. Molecular docking showed the interactions between DBL and α-D-glucose, N-acetyl-D-glucosamine, α-D-mannose, α-methyl-D-mannoside, ampicillin, and tetracycline. In addition, DBL showed antimicrobial activity with an MIC of 125 μg/mL and exerted synergistic effects in combination with ampicillin and tetracycline (fractional inhibitory concentration index ≤ 0.5). Additionally, DBL significantly inhibited biofilm formation and showed no toxicity in murine fibroblasts (p < 0.05). These results suggest that DBL exhibits antimicrobial activity and works synergistically with antibiotics.

Oxazinomycin arrests RNA polymerase at the polythymidine sequences

Oxazinomycin is a C-nucleoside antibiotic that is produced by Streptomyces hygroscopicus and closely resembles uridine. Here, we show that the oxazinomycin triphosphate is a good substrate for bacterial and eukaryotic RNA polymerases (RNAPs) and that a single incorporated oxazinomycin is rapidly extended by the next nucleotide. However, the incorporation of several successive oxazinomycins or a single oxazinomycin in a certain sequence context arrested a fraction of the transcribing RNAP. The addition of Gre RNA cleavage factors eliminated the transcriptional arrest at a single oxazinomycin and shortened the nascent RNAs arrested at the polythymidine sequences suggesting that the transcriptional arrest was caused by backtracking of RNAP along the DNA template. We further demonstrate that the ubiquitous C-nucleoside pseudouridine is also a good substrate for RNA polymerases in a triphosphorylated form but does not inhibit transcription of the polythymidine sequences. Our results collectively suggest that oxazinomycin functions as a Trojan horse substrate and its inhibitory effect is attributable to the oxygen atom in the position corresponding to carbon five of the uracil ring.

Advances in C-alkynylation of sugars and its application in organic synthesis

C-Glycosidation plays a significant role in the synthesis of optically active scaffolds.

Recent advances in biosensing using magnetic glyconanoparticles

In this critical review we discuss the most recent advances in the field of biosensing applications of magnetic glyconanoparticles. We first give an overview of the main synthetic routes to obtain magnetic-nanoparticle-carbohydrate conjugates and then we highlight their most promising applications for magnetic relaxation switching sensing, cell and pathogen detection, cell targeting and magnetic resonance imaging. We end with a critical perspective of the field, identifying the main challenges to be overcome, but also the areas where the most promising developments are likely to happen in the coming decades.

A mild and efficient Zn-catalyzed C-glycosylation: synthesis of C(2)–C(3) unsaturated C-linked glycopyranosides

A mild and efficient protocol for the C-glycosylation from glycals is described by using Zn-catalysis.

Synthesis and cytotoxicity of 2,3-enopyranosyl C-linked conjugates of genistein

A series of glycoconjugates, derivatives of genistein containing a C-glycosylated carbohydrate moiety, were synthesized and their anticancer activity was tested in vitro in the human cell lines HCT 116 and DU 145. The target compounds 15–17 were synthesized by treating ω-bromoalkyl C-glycosides derived from l-rhamnal (1) with a tetrabutylammonium salt of genistein. The new, metabolically stable analogs of previously studied O-glycosidic genistein derivatives inhibited proliferation of cancer cell lines through inhibition of the cell cycle.

Efficient carbon-Ferrier rearrangement on glycals mediated by ceric ammonium nitrate: Application to the synthesis of 2-deoxy-2-amino-C-glycoside

A carbon-Ferrier rearrangement on glycals has been performed by using ceric ammonium nitrate to obtain products in moderate to good yields with high selectivity. The versatility of this method has been demonstrated by applying it to differently protected glycals and by employing several nucleophiles. The obtained C-allyl glycoside has been utilized for the synthesis of a orthogonally protected 2-amino-2-deoxy-C-glycoside.

Multivalent alteration of quorum sensing in Staphylococcus aureus

Virulence in Staphylococcus aureus is strongly and positively correlated with local cell density. Here we present an effective approach to modulate this group behaviour using multivalent peptide-polymer conjugates. Our results show that by attaching multiple AIP-4' units to macromolecular scaffolds, the agr QS response in S. aureus was affected strongly, while displaying a clear multivalency effect.

Chemoenzymatic synthesis of novel C-ribosylated naphthoquinones

The biological activity of many natural products is dependent on the presence of carbohydrate units, which are usually attached via an O-glycosidic linkage by glycosyltransferases. Recently, an exceptional C-ribosylation event was discovered in the biosynthesis of the polyketide antibiotic alnumycin A. The two-step process involves initial attachment of d-ribose-5-phosphate to the polyaromatic aglycone by the C-glycosynthase AlnA and subsequent dephosphorylation by AlnB, an enzyme of the haloacid dehalogenase family. Here, we tested 23 unnatural substrates to probe the C-ribosylation reaction. The chemoenzymatic synthesis of C-ribosylated juglone, 7-methyl juglone, monomethyl naphthazarin, 8-chloro-7-methyl juglone, and 9-hydroxy-1,4-anthraquinone revealed the importance of a 1,4-quinoid system with an adjacent phenolic ring in order for reaction to occur. To further rationalize the molecular basis for reactivity, factors governing substrate recognition were investigated by NMR binding experiments. Additionally, the suitability of substrates for nucleophilic substitution was assessed by molecular modeling using density functional theory (DFT) calculations.

Responsive materials for self-regulated insulin delivery

With diabetes mellitus becoming an important public health concern, insulin-delivery systems are attracting increasing interest from both scientific and technological researchers. This feature article covers the present state-of-the-art glucose-responsive insulin-delivery system (denoted as GRIDS), based on responsive polymer materials, a promising system for self-regulated insulin delivery. Three types of GRIDS are discussed, based on different fundamental mechanisms of glucose-recognition, with: a) glucose enzyme, b) glucose binding protein, and c) synthetic boronic acid as the glucose-sensitive component. At the end, a personal perspective on the major issues yet to be worked out in future research is provided.

Switchable binding affinity of mannose tethered to collagen peptide by temperature-dependent triple-helix formation

Novel glycopeptides were created with a view to regulate the bindings of carbohydrates to lectins as a means of controlling biological function. We synthesized glycopeptides containing mannose (Man) tethered to a collagen peptide moiety (MPOG10: -(Pro-Hyp-Gly)10- or MGPP10: -(Gly-Pro-Pro)10-). Circular dichroism spectra showed formation of a triple helical structure for MPOG10, and the melting temperature indicates that MPOG10 forms a more stable triple helical structure than MGPP10 in phosphate buffered saline (PBS). At 25 °C, fluorescence polarization (FP) values of MPOG10 and MGPP10 increased following the addition of concanavalin A (ConA), and the addition of α-methyl-mannose (MeMan) to a mixed solution of each glycopeptide with ConA resulted in a decrease in FP values. These results confirm that the previous increase in FP values observed was caused by ConA binding to Man on MPOG10 or MGPP10. The binding affinity of MPOG10 was higher than that of MGPP10, and the dissociation constant of MPOG10 to ConA was 1.9 × 10(-5) (mol/L). The observed binding of MPOG10 to ConA at 25 °C was reduced at higher temperature (50 °C). Therefore, the enhanced binding affinity of MPOG10 to ConA could be accounted for by formation of a clustered Man moiety triggered by the formation of a more stable triple helical structure of MPOG10 compared with MGPP10.

Pharmaceutical properties and toxicology of Dioclea grandiflora

CONTEXT

Since the beginning of civilization, herbal medicines have been an important source for human beings to treat their ailments. Despite the large number of synthetic remedies available in the market, the use of plants is seen as a great challenge in the search for new substances endowed with therapeutic properties. One example is Dioclea grandiflora Mart. ex Benth. (Leguminosae) employed in traditional medicine to treat prostate disorders and kidney stones.

OBJECTIVES

This work presents a brief overview of D. grandiflora, including a description of the plant, its chemical composition and pharmacological properties.

METHODS

This review gathers information available in the scientific literature compiled from databases such as Science Direct, PubMed, Dr. Dukes Phytochemical and Ethnobotany, Missouri Botanical Garden and The International Plant Names Index.

RESULTS

The information found in the literature showed that flavonoids are the major constituents of D. grandiflora that account for most of the pharmacological properties so far disclosed. Several studies have revealed that D. grandiflora possesses antinociceptive, cardiovascular, antioxidant and anti-inflammatory activities.

CONCLUSION

Research shows that D. grandiflora is a potential source of compounds pertaining medicinal applications. It provides an interesting subject in the search for new drugs of natural origin.

Hybrid immobilization of galactosyl lactose and cellobiose on a gold substrate to modulate biological responses

Bioactive O-β-d-galactopyranosyl-(1→4)-O-β-d-galactopyranosyl-(1→4)-d-glucopyranose (4'-galactosyl lactose) was site-selectively modified at a reducing end with thiosemicarbazide (TSC). As-synthesized 4'-galactosyl lactose-TSC was immobilized on a gold substrate with cellobiose-TSC as a spacer through spontaneous self-assembly chemisorption via SAu bonding. Quartz crystal microbalance analysis suggested the successful formation of self-assembled monolayers (SAMs) of 4'-galactosyl lactose-TSC and/or cellobiose-TSC. Galactose-binding lectin exhibited the highest affinity for hybrid SAMs with an equimolar ratio of the two oligosaccharide-TSCs, while glucose-binding lectin showed decreasing adsorption with a decrease in cellobiose-TSC ratios. Human hepatocellular carcinoma cells, which recognize galactose residues, efficiently adhered to the hybrid SAMs. Higher enzymatic deethoxylation of ethoxyresorufin via cytochrome P450 appeared on hybrid SAMs. These results suggested that clustering of the bioactive sugars was involved in the cellular responses, possibly via biological carbohydrate-protein interactions. This approach to designing carbohydrate-based scaffolds should provide a basis for the functional development of glyco-decorated biointerfaces for cell culture applications.

Structural basis for C-ribosylation in the alnumycin A biosynthetic pathway

Alnumycin A is an exceptional aromatic polyketide that contains a carbohydrate-like 4'-hydroxy-5'-hydroxymethyl-2',7'-dioxane moiety attached to the aglycone via a carbon-carbon bond. Recently, we have identified the D-ribose-5-phosphate origin of the dioxane unit and demonstrated that AlnA and AlnB are responsible for the overall C-ribosylation reaction. Here, we provide direct evidence that AlnA is a natural C-glycosynthase, which catalyzes the attachment of D-ribose-5-phosphate to prealnumycin by formation of the C(8)-C(1') bond as demonstrated by the structure of the intermediate alnumycin P. This compound is subsequently dephosphorylated by AlnB, an enzyme of the haloacid dehalogenase superfamily. Structure determination of the native trimeric AlnA to 2.1-Å resolution revealed a highly globular fold encompassing an α/β/α sandwich. The crystal structure of the complex with D-ribose-5-phosphate indicated that the phosphosugar is bound in the open-chain configuration. Identification of residues E29, K86, and K159 near the C-1 carbonyl of the ligand led us to propose that the carbon-carbon bond formation proceeds through a Michael-type addition. Determination of the crystal structure of the monomeric AlnB in the open conformation to 1.25-Å resolution showed that the protein consists of core and cap domains. Modeling of alnumycin P inside the cap domain positioned the phosphate group next to a Mg(2+) ion present at the junction of the domains. Mutagenesis data were consistent with the canonical reaction mechanism for this enzyme family revealing the importance of residues D15 and D17 for catalysis. The characterization of the prealnumycin C-ribosylation illustrates an alternative means for attachment of carbohydrates to natural products.

Biosynthetic pathway toward carbohydrate-like moieties of alnumycins contains unusual steps for C-C bond formation and cleavage

Carbohydrate moieties are important components of natural products, which are often imperative for the solubility and biological activity of the compounds. The aromatic polyketide alnumycin A contains an extraordinary sugar-like 4'-hydroxy-5'-hydroxymethyl-2',7'-dioxane moiety attached via a carbon-carbon bond to the aglycone. Here we have extensively investigated the biosynthesis of the dioxane unit through (13)C labeling studies, gene inactivation experiments and enzymatic synthesis. We show that AlnA and AlnB, members of the pseudouridine glycosidase and haloacid dehalogenase enzyme families, respectively, catalyze C-ribosylation conceivably through Michael-type addition of d-ribose-5-phosphate and dephosphorylation. The ribose moiety may be attached both in furanose (alnumycin C) and pyranose (alnumycin D) forms. The C(1')-C(2') bond of alnumycin C is subsequently cleaved and the ribose unit is rearranged into an unprecedented dioxolane (cis-bicyclo[3.3.0]-2',4',6'-trioxaoctan-3'β-ol) structure present in alnumycin B. The reaction is catalyzed by Aln6, which belongs to a previously uncharacterized enzyme family. The conversion was accompanied with consumption of O(2) and formation of H(2)O(2), which allowed us to propose that the reaction may proceed via hydroxylation of C1' followed by retro-aldol cleavage and acetal formation. Interestingly, no cofactors could be detected and the reaction was also conducted in the presence of metal chelating agents. The last step is the conversion of alnumycin B into the final end-product alnumycin A catalyzed by Aln4, an NADPH-dependent aldo-keto reductase. This characterization of the dioxane biosynthetic pathway sets the basis for the utilization of C-C bound ribose, dioxolane and dioxane moieties in the generation of improved biologically active compounds.

Stavudine-loaded mannosylated liposomes: in-vitro anti-HIV-I activity, tissue distribution and pharmacokinetics

Cells of the mononuclear phagocyte system (MPS) are important hosts for human immunodeficiency virus (HIV). Lectin receptors, which act as molecular targets for sugar molecules, are found on the surface of these cells of the MPS. Stavudine-loaded mannosylated liposomal formulations were developed for targeting to HIV-infected cells. The mannose-binding protein concanavalin A was employed as model system for the determination of in-vitro ligand-binding capacity. Antiretroviral activity was determined using MT-2 cell line. Haematological changes, tissue distribution and pharmacokinetic studies of free, liposomal and mannosylated liposomal drug were performed following a bolus intravenous injection in Sprague-Dawley rats. The entrapment efficiency of mannosylated liposomes was found to be 47.H ± 1.57%. Protein-carbohydrate interaction has been utilized for the effective delivery of mannosylated formulations. Cellular drug uptake was maximal when mannosylated liposomes were used. MT2 cells treated continuously with uncoated liposomal formulation had p24 levels 8–12 times lower than the level of free drug solution. Further, the mannosylated liposomes have shown p24 levels that were 14–20 and 1.42.3 times lower than the level of free drug and uncoated liposomal formulation treatment, respectively. Similar results were observed when infected MT2 cells were treated overnight. Stavudine, either given plain or incorporated in liposomes, led to development of anaemia and leucocytopenia while mannosylated liposomes overcame these drawbacks. These systems maintained a significant level of stavudine in the liver, spleen and lungs up to 12 h and had greater systemic clearance as compared with free drug or the uncoated liposomal formulation. Mannosylated liposomes have shown potential for the site-specific and ligand-directed delivery systems with desired therapeutics and better pharmacological activity.

Staurosporine tethered peptide ligands that target cAMP-dependent protein kinase (PKA): optimization and selectivity profiling

We have recently developed a fragment based selection strategy for targeting kinases, where a small molecule warhead can be non-covalently tethered to a phage-displayed library of peptides. This approach was applied to the conversion of the promiscuous kinase inhibitor, staurosporine, into a potent bivalent ligand for cAMP-dependent protein kinase (PKA). Herein we report a systematic evaluation of this new bivalent ligand (BL); (a) Lineweaver-Burke analysis revealed that the BL, unlike substrate-based bivalent kinase inhibitors, displayed non-competitive inhibition with respect to the peptide substrate, suggesting an allosteric mechanism of action; (b) linker optimization of the BL, afforded one of the most potent, sub-nanomolar, inhibitors of PKA reported to date; (c) the BL was found to be modular, where attachment of active site targeted small molecule warheads in lieu of staurosporine could achieve similar gains in affinity; and (d) profiling studies of both the staurosporine derivative and the BL (amide isostere) against a panel of 90 kinases revealed almost unique enhancement in selectivity against PKA (>5-fold) compared to the starting staurosporine derivative. These combined results provide new insights for BL discovery, which has the potential to provide guidance toward the development of kinase selective reagents while uncovering new allosteric sites on kinases for therapeutic targeting.

Measurement of monovalent and polyvalent carbohydrate-lectin binding by back-scattering interferometry

Carbohydrate-protein binding is important to many areas of biochemistry. Here, backscattering interferometry (BSI) has been shown to be a convenient and sensitive method for obtaining quantitative information about the strengths and selectivities of such interactions. The surfaces of glass microfluidic channels were covalently modified with extravidin, to which biotinylated lectins were subsequently attached by incubation and washing. The binding of unmodified carbohydrates to the resulting avidin-immobilized lectins was monitored by BSI. Dose-response curves that were generated within several minutes and were highly reproducible in multiple wash/measure cycles provided adsorption coefficients that showed mannose to bind to concanavalin A (conA) with 3.7 times greater affinity than glucose consistent with literature values. Galactose was observed to bind selectively and with similar affinity to the lectin BS-1. The avidities of polyvalent sugar-coated virus particles for immobilized conA were much higher than monovalent glycans, with increases of 60-200 fold per glycan when arrayed on the exterior surface of cowpea mosaic virus or bacteriophage Qbeta. Sugar-functionalized PAMAM dendrimers showed size-dependent adsorption, which was consistent with the expected density of lectins on the surface. The sensitivity of BSI matches or exceeds that of surface plasmon resonance and quartz crystal microbalance techniques, and is sensitive to the number of binding events, rather than changes in mass. The operational simplicity and generality of BSI, along with the near-native conditions under which the target binding proteins are immobilized, make BSI an attractive method for the quantitative characterization of the binding functions of lectins and other proteins.

Surface plasmon resonance imaging of limited glycoprotein samples

A surface plasmon resonance imaging method has been developed for high throughput recognition and determination of low level glycoproteins with limited sample volume at least down to 50 nL. Chicken ovalbumin and immunoglobulin G were chosen as model compounds while bovine serum albumin and lysozyme were used as control. Each protein, at a concentration of 0.0080-1.0 mg mL(-1), was printed on one gold sensing film, and the films were simultaneously reacted with a probe solution and viewed using a laboratory-built surface plasmon resonance imaging system. The imaging signals were dependent on the concentration and the type of analyte, with a limit of detection down to at least 0.5 ng. The glycoproteins dotted at either 1.0 mg mL(-1) or 0.010 mg mL(-1) were easily differentiated from the non-glycoproteins by reaction with 200 nM concanavalin A (con A), giving a limit of recognition down also to 0.5 ng glycoprotein. This imaging method was hence considered a new tool for analyzing glycoproteins.

The conformational behaviour and P-selectin inhibition of fluorine-containing sialyl LeX glycomimetics

A combination of experimental J/NOE NMR data with molecular mechanics and dynamics calculations has been used to examine the conformational behaviour and assign the configuration of synthetically prepared epimeric 3-carboxymethyl-O-Gal-(1-->1)-alpha-Man-fluoro-C-glycosides. It is shown that the population distributions around the glycosidic linkages strongly depend on the configuration at the fluorinated carbon of the pseudoacetal residue. It is also shown that these compounds resemble the inhibition ability of sialyl LeX towards P-selectin.

Chemical probes of UDP-galactopyranose mutase

Many pathogenic prokaryotes and eukaryotes possess the machinery required to assemble galactofuranose (Galf)-containing glycoconjugates; these glycoconjugates can be critical for virulence or viability. Accordingly, compounds that block Galf incorporation may serve as therapeutic leads or as probes of the function of Galf-containing glycoconjugates. The enzyme UDP-galactopyranose mutase (UGM) is the only known generator of UDP-galactofuranose, the precursor to Galf residues. We previously employed a high-throughput fluorescence polarization assay to investigate the Klebsiella pneumoniae UGM. We demonstrate the generality of this assay by extending it to UGM from Mycobacterium tuberculosis. To identify factors influencing binding, we synthesized a directed library containing a 5-arylidene-2-thioxo-4-thiazolidinone core, a structure possessing features common to ligands for both homologs. Our studies offer a blueprint for identifying inhibitors of the growing family of UGM homologs and provide insight into UGM inhibition.

2′-Carboxybenzyl glycosides: glycosyl donors for C-glycosylation and conversion into other glycosyl donors

Glycosylation of various glycosyl acceptors with 2'-carboxybenzyl (CB) 2,3,4,6-tetra-O-benzyl-beta-D-glucopyranoside and CB 2,3,4,6-tetra-O-benzyl-alpha-D-mannopyranoside as glycosyl donors afforded alpha-C-glycosides exclusively or predominantly in good yields. CB glycosides were also converted to other well-known glycosyl donors, the corresponding phenyl thioglycoside and the glycosyl fluoride derivatives.

Altered expression and glycosylation of plasma proteins in rheumatoid arthritis

Altered glycosylation of plasma proteins has been directly implicated in the pathogenesis of rheumatoid arthritis (RA). The present study investigated the changes in the Concanavalin-A (Con-A)-bound plasma proteins in the RA patients in comparison to that of the healthy controls. Two proteins (MW approximately 32 kDa and approximately 62 kDa) showed an alteration in expression while an altered monosaccharide profile (high mannose) was observed in the approximately 62 kDa protein in the samples collected from RA patients. The 2-dimensional polyacrylamide gel electrophoresis analysis of the Con-A-bound plasma samples showed a large number of protein spots, a few of which were differentially expressed in the RA patients. Some unidentified proteins were detected in the RA patients which were absent in the control samples. The present study, therefore, enunciates the role of carbohydrates as well as that of the acute phase response in the disease pathogenesis.

Recognition of septanose carbohydrates by concanavalin A

The ability of the jack bean lectin concanavalin A (ConA) to bind seven membered ring (septanose) monosaccharides has been investigated by isothermal titration calorimetry (ITC) and saturation transfer difference (STD) NMR spectroscopy.

SPR Studies of Carbohydrate-Protein Interactions: Signal Enhancement of Low-Molecular-Mass Analytes by Organoplatinum(II)-Labeling

The relatively insensitive surface plasmon resonance (SPR) signal detection of low-molecular-mass analytes that bind with weak affinity to a protein--for example, carbohydrate-lectin binding--is hampering the use of biosensors in interaction studies. In this investigation, low-molecular-mass carbohydrates have been labeled with an organoplatinum(II) complex of the type [PtCl(NCN-R)]. The attachment of this complex increased the SPR response tremendously and allowed the detection of binding events between monosaccharides and lectins at very low analyte concentrations. The platinum atom inside the organoplatinum(II) complex was shown to be essential for the SPR-signal enhancement. The organoplatinum(II) complex did not influence the specificity of the biological interaction, but both the signal enhancement and the different binding character of labeled compounds when compared with unlabeled ones makes the method unsuitable for the direct calculation of biologically relevant kinetic parameters. However, the labeling procedure is expected to be of high relevance for qualitative binding studies and relative affinity ranking of small molecules (not restricted only to carbohydrates) to receptors, a process of immense interest in pharmaceutical research.

Lectin affinity capillary electrophoresis in glycoform analysis applying the partial filling technique

The study of protein glycosylation and its significance in biological interactions is a field of growing interest. This work demonstrates a lectin-based separation of protein glycoforms of alpha1-acid glycoprotein (AGP or orosomucoid) with capillary electrophoresis. Glycoform analysis was performed with a "partial filling technique" with the lectin Concanavalin A (Con A) as affinity ligand. Con A separated human AGP into two peaks; the first peak included AGP glycoforms without biantennary glycans, and the second peak represented the fraction that had one or more biantennary glycans. The applicability of the method was demonstrated with the analysis of AGP from clinical samples and AGP treated with N-glycosidase F. The AGP separation was also used as a reporter system to estimate the dissociation constant (KD) between Con A and a competing sugar.

Synthesis of 2,3-unsaturated C-glycosides by HClO4–SiO2 catalyzed Ferrier rearrangement of glycals

Alkyl 2,3-unsaturated C-glycopyranosides have been prepared by Ferrier rearrangement of acyl or alkyl protected glycals catalyzed by HClO(4)-SiO(2).

Substitution and Remote Protecting Group Influence on the Oxidation/Addition of α-Substituted 1,2-Anhydroglycosides: A Novel Entry into C-Ketosides

[reaction: see text] C-Ketosides are valuable intermediates in chemical synthesis and as glycoside mimics. This manuscript describes the efficient generation of these substrates from alpha-alkyl-substituted glycals and an oxidative, C-C bond-forming sequence where the choice of C(3) protecting group was critical.

Investigation of the interaction between peanut agglutinin and synthetic glycopolymeric multivalent ligands

The interaction between synthetic glycoplymers bearing beta-D-galactose side groups and the lectin peanut agglutinin (PNA) was investigated by UV-difference spectroscopy and isothermal titration calorimetry (ITC). UV-difference spectroscopy indicated that the polymer-lectin interaction was stronger than that between PNA and either the corresponding monomer, D-galactose or D-lactose. The thermodynamics of binding (K, DeltaG, DeltaH, DeltaS and n) were determined from ITC data by fitting with a two-site, non-cooperative binding model. It was found that the glycopolymer displayed around a 50 times greater affinity for the lectin than the parent carbohydrate, and around 10 times greater than the monomer, on a valency-corrected basis. Binding was found to be entropically driven, and was accompanied by aggregation and precipitation of protein molecules. Furthermore, interesting differences between polymers prepared either from deacetylated monomers, or by deacetylation of pre-formed polymers, were found.

Sensing capabilities of colloidal gold modified with a self-assembled monolayer of a glucose-carrying polymer chain on a glass substrate

A disulfide-carrying polymer with pendent glucose residues (poly(2-methacryloyloxyethyl D-glucopyranoside)) was obtained by using a benzyl N,N-diethyldithiocarbamoyl derivative which shows the abilities of initiation, chain transfer, and termination (iniferter). The disulfide-carrying polymer was accumulated on a colloidal Au-immobilized glass substrate, and the usefulness of the polymer as a sensing element of concanavalin A (Con A) was examined by using a UV-visible spectrophotometer with the help of surface plasmon resonance. The sensor showed a concentration-dependent specific binding of Con A with a detection limit of 1.9 nM, and furthermore, it had a very high stability at high ionic strength. The polymer-coated device examined here was not only useful as a simple biosensor chip but is also expected to expand our knowledge of interfacial phenomena by introducing various functional polymers on colloidal Au.

α-C-Mannosyltryptophan is not recognized by conventional mannose-binding lectins

Alpha-C-mannosyltryptophan (C-Man-Trp) is a novel, naturally occurring C-linked carbohydrate-protein linkage first found in 1994 from human ribonuclease 2. Since then, a number of C-Man-Trp residue have been found from several important proteins such as interleukin 12 beta, components of complement system, thrombospondin-1, and erythropoietin receptor, however, the biological functions have remained unknown even though its biosynthetic pathway has been revealed. In order to find a clue as to the biological functions, we examined the affinity of C-Man-Trp with conventional mannose lectin such as concanavarin A (Con A) and mannose-binding lectin (MBL). The affinity of C-Man-Trp with Con A, a typical mannose-binding lectin from plant was examined using a Con A-Sepharose column. Unlike p-nitrophenyl-alpha-O-Man, C-Man-Trp was not retained on the column. MBL-C, a major mannose-binding lectin purified from mouse serum, did not bind with N-biotinylated C-Man-Trp, judging from ELISA based assay. These results imply that C-Man-Trp may be recognized with the other specific proteins associated with its unknown biological functions.