Divergent synthesis of 48 heparan sulfate-based disaccharides and probing the specific sugar-fibroblast growth factor-1 interaction.

Several biological processes involve glycans, yet understanding their ligand specificities is impeded by their inherent diversity and difficult acquisition. Generating broad synthetic sugar libraries for bioevaluations is a powerful tool in unraveling glycan structural information. In the case of the widely distributed heparan sulfate (HS), however, the 48 theoretical possibilities for its repeating disaccharide call for synthetic approaches that should minimize the effort in an undoubtedly huge undertaking. Here we employed a divergent strategy to afford all 48 HS-based disaccharides from just two orthogonally protected disaccharide precursors. Different combinations and sequence of transformation steps were applied with many downstream intermediates leading up to multiple target products. With the full disaccharide library in hand, affinity screening with fibroblast growth factor-1 (FGF-1) revealed that four of the synthetic sugars bind to FGF-1. The molecular details of the interaction were further clarified through X-ray analysis of the sugar-protein cocrystals. The capability of comprehensive sugar libraries in providing key insights in glycan-ligand interaction is, thus, highlighted.

Synthesis of heparin oligosaccharides and their interaction with eosinophil-derived neurotoxin.

A convenient route for the synthesis of heparin oligosaccharides involving regioselective protection of D-glucosamine and a concise preparation of rare L-ido sugars from diacetone α-D-glucose is described. Stereoselective coupling of a D-glucosamine-derived trichloroacetimidate with a 1,6-anhydro-ß-L-idopyranosyl 4-alcohol gave the desired α-linked disaccharide, which was used as repeating unit for dual chain elongation and termination. Stepwise assembly from the reducing to the non-reducing end with a D-glucosamine-derived monosaccharide as starting unit furnished the oligosaccharide skeletons having different chain lengths. A series of functional group transformations afforded the expected heparin oligosaccharides with 3, 5 and 7 sugar units. Interaction of these oligosaccharides with eosinophil-derived neurotoxin (EDN), a cationic ribonuclease and a mediator produced by human eosinophils, was further investigated. The results revealed that at 5 µg mL(-1), the heptasaccharide has sufficiently strong interference to block EDN binding to Beas-2B cells. The tri- and pentasaccharides have moderate inhibitory properties at 50 µg mL(-1) concentration, but no inhibition has been observed at 10 µg mL(-1). The IC(50) values of the tri-, penta- and heptasaccharides are 69.4, 47.2 and 0.225 µg mL(-1), respectively.

The Good, the Bad, and the Ugly Memories of Carbohydrate Fragments in Collision-Induced Dissociation.

Collision-induced dissociation (CID) tandem mass spectrometry is commonly used for carbohydrate structural determinations. In the CID tandem mass spectrometry approach, carbohydrates are dissociated into fragments, and this is followed by the structural identification of fragments through subsequent CID. The success of the structural analysis depends on the structural correlation of fragments before and after dissociation, that is, structural memory of fragments. Fragments that completely lose the memory of their original structures cannot be used for structural analysis. By contrast, fragments with extremely strong correlations between the structures before and after fragmentation retain the information on their original structures as well as have memories of their precursors' entire structures. The CID spectra of these fragments depend on their own structures and on the remaining parts of the precursor structures, making structural analysis impractical. For effective structural analysis, the fragments produced from a precursor must have good structural memory, meaning that the structures of these fragments retain their original structure, and they must not be strongly affected by the remaining parts of the precursors. In this study, we found that most of the carbohydrate fragments produced by low-energy CID have good memory in terms of linkage position and anomericity. Fragments with ugly memory, where fragment structures change with the remaining parts of the precursors, can be attributed to C ion formation in a linear form. Fragments with ugly memory can be changed to have good memory by preventing linear C ion generation by using an alternative CID sequence, or the fragments of ugly memory can become useful in structural analysis when the contribution of linear C ions in fragmentation patterns is understood.

Regioselective one-pot protection of D-glucosamine.

A highly regioselective one-pot transformation of 2-azido-2-deoxy-1,3,4,6-tetra-O-trimethylsilyl-d-glucopyranose via sequential additions of various reagents was systematically studied, yielding the fully protected derivatives and the 1-, 3-, 4-, as well as 6-alcohols, respectively.

Smartphone assisted colorimetric and fluorescent triple-channel signal sensor for ascorbic acid assay based on oxidase-like CoOOH nanoflakes.

Ascorbic acid (AA) is an important diet-derived antioxidant to human body. Thus, efficient and accurate detection of AA is of considerable significance in food analysis. Herein, smartphone assisted colorimetric and fluorescent triple-channel signal sensor has been developed for AA monitoring based on oxidase-like CoOOH nanoflakes. CoOOH nanoflakes can efficiently catalyze the oxidation of p-phenylenediamine (p-PD) into reddish brown p-PDox. The carbon dots (C-dots) are further introduced, of which the fluorescence can be quenched by p-PDox. However, in the presence of AA, the CoOOH nanoflakes is reduced and thus collapsed. As a result, the oxidation of p-PD is restrained, and thus the fluorescence of C-dots keeps strong. Based on AA induced light color, low absorbance, and strong fluorescence, triple-channel signal sensor has been proposed for AA determination. The AA assay shows a dynamic response range from 0.5 to 10 µM with a detection limit of 0.09 µM. The method assay allows detection of AA in real samples such as fruit juices. Combination with portable smartphone, the developed sensor is potential for AA determination in resource-poor settings.

Interactions that influence the binding of synthetic heparan sulfate based disaccharides to fibroblast growth factor-2.

Heparan sulfate (HS) is a linear sulfated polysaccharide that mediates protein activities at the cell-extracellular interface. Its interactions with proteins depend on the complex patterns of sulfonations and sugar residues. Previously, we synthesized all 48 potential disaccharides found in HS and used them for affinity screening and X-ray structural analysis with fibroblast growth factor-1 (FGF1). Herein, we evaluated the affinities of the same sugars against FGF2 and determined the crystal structures of FGF2 in complex with three disaccharides carrying N-sulfonated glucosamine and 2-O-sulfonated iduronic acid as basic backbones. The crystal structures show that water molecules mediate different interactions between the 3-O-sulfonate group and Lys125. Moreover, the 6-O-sulfonate group forms intermolecular interactions with another FGF2 unit apart from the main binding site. These findings suggest that the water-mediated interactions and the intermolecular interactions influence the binding affinity of different disaccharides with FGF2, correlating with their respective dissociation constants in solution.

Synthesis of L-hexoses and their related biomolecules.

Carbohydrates either conjugated or as free entities are major players in numerous biological processes. The desire to comprehend the nature of their functions and further develop therapeutic and diagnostic applications has fuelled the recent upsurge in the glycoscience field. Mainly accessed through chemical synthesis, homogeneous and well-defined sugar constructs are on high demand for structure-activity evaluation. Although the d-sugars, particularly the d-hexoses, have dominated the carbohydrate landscape, L-hexoses also attracted attention because they are known components of important polysaccharides, antibiotics, and other natural products. Nonetheless, the L-hexose-based materials needed for making building blocks for sugar assemblies are rare and are usually expensive if commercially available. Thus, intense efforts were focused on the development of innovative and reliable methods for the acquisition of L-hexoses and their derivatives. This review outlines several efficient and cost-effective routes for the chemical syntheses of L-hexoses, particularly focusing on approaches that utilize commercially abundant sugars as starting materials. A sampling of the applications of the generated L-hexoses in preparing biologically relevant compounds is also provided.