Synthesis and interaction with growth factors of sulfated oligosaccharides containing an anomeric fluorinated tail.

Compounds that mimic the biological properties of glycosaminoglycans (GAGs) and can be more easily prepared than the native GAG oligosaccharides are highly demanded. Here, we present the synthesis of sulfated oligosaccharides displaying a perfluorinated aliphatic tag at the reducing end as GAG mimetics. The preparation of these molecules was greatly facilitated by the presence of the fluorinated tail since the reaction intermediates were isolated by simple fluorous solid-phase extraction.

High-Mannose Oligosaccharide Hemimimetics that Recapitulate the Conformation and Binding Mode to Concanavalin A, DC-SIGN and Langerin.

The "carbohydrate chemical mimicry" exhibited by sp -iminosugars has been utilized to develop practical syntheses for analogs of the branched high-mannose-type oligosaccharides (HMOs) Man and Man . In these compounds, the terminal nonreducing Man residues have been substituted with 5,6-oxomethylidenemannonojirimycin (OMJ) motifs. The resulting oligomannoside hemimimetic accurately reproduce the structure, configuration, and conformational behavior of the original mannooligosaccharides, as confirmed by NMR and computational techniques.

Glycosaminoglycans: What Remains To Be Deciphered?

Glycosaminoglycans (GAGs) are complex polysaccharides exhibiting a vast structural diversity and fulfilling various functions mediated by thousands of interactions in the extracellular matrix, at the cell surface, and within the cells where they have been detected in the nucleus. It is known that the chemical groups attached to GAGs and GAG conformations comprise "glycocodes" that are not yet fully deciphered. The molecular context also matters for GAG structures and functions, and the influence of the structure and functions of the proteoglycan core proteins on sulfated GAGs and vice versa warrants further investigation.

Mannobioside biomimetics that trigger DC-SIGN binding selectivity.

Selective DC-SIGN targeting . langerin might lead to anti-infective agents, given their counteracting effects upon infection by some pathogens. Here we show that multivalent sp-iminosugar-containing mannobioside analogs can achieve total DC-SIGN selectivity by levering the canonic binding mode towards high-mannose oligosaccharide ligands, behaving as factual biomimics.

Pleiotrophin Interaction with Synthetic Glycosaminoglycan Mimetics.

Chondroitin sulfate (CS) E is the natural ligand for pleiotrophin (PTN) in the central nervous system (CNS) of the embryo. Some structures of PTN in solution have been solved, but no precise location of the binding site has been reported yet. Using N-labelled PTN and HSQC NMR experiments, we studied the interactions with a synthetic CS-E tetrasaccharide corresponding to the minimum binding sequence.

The Interaction between Chondroitin Sulfate and Dermatan Sulfate Tetrasaccharides and Pleiotrophin.

Pleiotrophin (PTN) is a neurotrophic factor that participates in the development of the embryonic central nervous system (CNS) and neural stem cell regulation by means of an interaction with sulfated glycosaminoglycans (GAGs). Chondroitin sulfate (CS) is the natural ligand in the CNS. We have previously studied the complexes between the tetrasaccharides used here and MK (Midkine) by ligand-observed NMR techniques.

Fluorous-Tag-Assisted Synthesis of GAG-Like Oligosaccharides.

The classic, solution-phase synthesis of glycosaminoglycan (GAG) oligosaccharides is hampered by the numerous, time-consuming chromatographic purifications required for the isolation of the glycosylation products after each coupling step between sugar building blocks. Here, we present a detailed experimental procedure for a glycosylation reaction involving a glycosyl acceptor unit that is equipped with a perfluorinated tag. The presence of this fluorous tail allows the quick purification of the desired glycosylation product by performing a simple fluorous solid-phase extraction (F-SPE).

Synthesis, self-assembly and Langerin recognition studies of a resorcinarene-based glycocluster exposing a hyaluronic acid thiodisaccharide mimetic.

Herein, we report the synthesis of an octavalent glycocluster exposing a thiodisaccharide mimetic of the repetitive unit of hyaluronic acid, βSGlcA(1 → 3)βSGlcNAc, constructed on a calix[4]resorcinarene scaffold by CuAAC reaction of suitable precursors. This glycocluster showed a strong tendency toward self-aggregation. DOSY-NMR and DLS experiments demonstrated the formation of spherical micelles of d ≅ 6.

GAG Multivalent Systems to Interact with Langerin.

Langerin is a C-type Lectin expressed at the surface of Langerhans cells, which play a pivotal role protecting organisms against pathogen infections. To address this aim, Langerin presents at least two recognition sites, one Ca-dependent and another one independent, which are capable to recognize a variety of carbohydrate ligands. In contrast to other lectins, Langerin recognizes sulfated glycosaminoglycans (GAGs), a family of complex and heterogeneous polysaccharides present in the cell membrane and the extracellular matrix, at the interphase generated in the trimeric form of Langerin but absent in the monomeric form.

Midkine Interaction with Chondroitin Sulfate Model Synthetic Tetrasaccharides and Their Mimetics: The Role of Aromatic Interactions.

Midkine (MK) is a neurotrophic factor that participates in the embryonic central nervous system (CNS) development and neural stem cell regulation, interacting with sulfated glycosaminoglycans (GAGs). Chondroitin sulfate (CS) is the natural ligand in the CNS. In this work, we describe the interactions between a library of synthetic models of CS-types and mimics.

Synthesis, structure and midkine binding of chondroitin sulfate oligosaccharide analogues.

The preparation of chondroitin sulfate (CS) oligosaccharide mimetics, more easily synthesized than natural sequences, is a highly interesting task because these compounds pave the way for modulation of the biological processes in which CS is involved. Herein, we report the synthesis of CS type E analogues which present easily accessible glucose units instead of glucuronic acid (GlcA) moieties. NMR experiments and molecular dynamics simulations showed that the 3D structure of these compounds is similar to the structure of the natural CS-E oligosaccharides.

Second-Generation Dendrimers with Chondroitin Sulfate Type-E Disaccharides as Multivalent Ligands for Langerin.

Chondroitin sulfate type-E (CS-E) is a sulfated polysaccharide that shows several interesting biological activities, such as modulation of the neuronal growth factor signaling and its interaction with langerin, a C-type lectin with a crucial role in the immunological system. However, applications of CS-E are hampered by the typical heterogeneous structure of the natural polysaccharide. Well-defined, homogeneous CS-E analogues are highly demanded.

Synthesis of (1→3) Thiodisaccharides of GlcNAc and the Serendipitous Formation of 2,3-Dideoxy-(1→2)-thiodisaccharides through a Vinyl Azide Intermediate.

The syntheses of β--GlcA(1→3)GlcNAc and β--Gal(1→3)GlcNAc thiodisaccharides, which can be considered mimetics of the repeating units of hyaluronan and keratan respectively, were achieved by S2 displacement of a triflate group allocated at the 3-position of a convenient 2-azido-4,6--benzylidene-2-deoxy-β-d-allopyranose precursor by the corresponding nucleophilic suitable protected thioaldoses derived from glucuronic acid (GlcA) and galactose (Gal). The study of the reaction led to the finding that the vinyl azide formed by competitive E2 reaction of the mentioned triflate was an interesting precursor of a new kind of 2,3-dideoxy-2-azido-(1→2) thiodisaccharides through an addition reaction. Determination of the stereochemistry of the new stereocenter at C-2 was achieved by NOESY experiments.

Synthesis of a Fluorous-Tagged Hexasaccharide and Interaction with Growth Factors Using Sugar-Coated Microplates.

Here, we report the synthesis of a sulfated, fully protected hexasaccharide as a glycosaminoglycan mimetic and the study of its interactions with different growth factors: midkine, basic fibroblast growth factor (FGF-2) and nerve growth factor (NGF). Following a fluorous-assisted approach, monosaccharide building blocks were successfully assembled and the target oligosaccharide was prepared in excellent yield. The use of more acid stable 4,6--silylidene protected glucosamine units was crucial for the efficiency of this strategy because harsh reaction conditions were needed in the glycosylations to avoid the formation of orthoester side products.

Unexpected loss of stereoselectivity in glycosylation reactions during the synthesis of chondroitin sulfate oligosaccharides.

Here, we present an exploratory study on the fluorous-assisted synthesis of chondroitin sulfate (CS) oligosaccharides. Following this approach, a CS tetrasaccharide was prepared. However, in contrast to our previous results, a significant loss of β-selectivity was observed in [2 + 2] glycosylations involving -trifluoroacetyl-protected D-galactosamine donors and D-glucuronic acid (GlcA) acceptors.

The Use of NMR to Study Transient Carbohydrate-Protein Interactions.

Carbohydrates are biologically ubiquitous and are essential to the existence of all known living organisms. Although they are better known for their role as energy sources (glucose/glycogen or starch) or structural elements (chitin or cellulose), carbohydrates also participate in the recognition events of molecular recognition processes. Such interactions with other biomolecules (nucleic acids, proteins, and lipids) are fundamental to life and disease.

Fluorous-tag assisted synthesis of a glycosaminoglycan mimetic tetrasaccharide as a high-affinity FGF-2 and midkine ligand.

Here, we present the preparation of a sulfated, fully protected tetrasaccharide derivative following the glycosaminoglycan (GAG)-related sequence GlcNAc-β(1 → 4)-Glc-β(1 → 3). The tetramer was efficiently assembled via an iterative glycosylation strategy using monosaccharide building blocks. A fluorous tag was attached at position 6 of the reducing end unit enabling the purification of reaction intermediates by simple fluorous solid phase extraction.

Rational-Differential Design of Highly Specific Glycomimetic Ligands: Targeting DC-SIGN and Excluding Langerin Recognition.

At the surface of dendritic cells, C-type lectin receptors (CLRs) allow the recognition of carbohydrate-based PAMPS or DAMPS (pathogen- or danger-associated molecular patterns, respectively) and promote immune response regulation. However, some CLRs are hijacked by viral and bacterial pathogens. Thus, the design of ligands able to target specifically one CLR, to either modulate an immune response or to inhibit a given infection mechanism, has great potential value in therapeutic design.

Interactions between a Heparin Trisaccharide Library and FGF-1 Analyzed by NMR Methods.

FGF-1 is a potent mitogen that, by interacting simultaneously with Heparan Sulfate Glycosaminoglycan HSGAG and the extracellular domains of its membrane receptor (FGFR), generates an intracellular signal that finally leads to cell division. The overall structure of the ternary complex Heparin:FGF-1:FGFR has been finally elucidated after some controversy and the interactions within the ternary complex have been deeply described. However, since the structure of the ternary complex was described, not much attention has been given to the molecular basis of the interaction between FGF-1 and the HSGAG.

Glycodendrimers as Chondroitin Sulfate Mimetics: Synthesis and Binding to Growth Factor Midkine.

Chondroitin sulfate (CS) is a member of the glycosaminoglycan (GAG) family, a class of polysaccharides implicated in relevant biological functions. The structural complexity of these carbohydrates demands the development of simple glycomimetics as useful tools to study the biological processes in which GAGs are involved. In this work we described the synthesis of the disaccharide unit of the CS-E (GlcA-GalNAc(4,6-di-OSO )), in a multivalent presentation.

Flavonoid glycosides from Persea caerulea. Unraveling their interactions with SDS-micelles through matrix-assisted DOSY, PGSE, mass spectrometry, and NOESY.

Two flavonoid glycosides derived from rhamnopyranoside (1) and arabinofuranoside (2) have been isolated from leaves of Persea caerulea for the first time. The structures of 1 and 2 have been established by H NMR, C NMR, and IR spectroscopy, together with LC-ESI-TOF and LC-ESI-IT MS spectrometry. From the MS and MS/MS data, the molecular weights of the intact molecules as well as those of quercetin and kaempferol together with their sugar moieties were deduced.

Anaerobic co-digestion of agro-food waste mixtures in a fed-batch basis.

The agro-food industry (including livestock) generates millions of tonnes of waste products. A solution to this sector's waste disposal challenges was explored by a joint treatment model of organic waste products from several industries. An inventory of agro-food industry organic waste streams with high potential for biogas production was carried out in a logistically viable area (Cider Region, Asturias, Spain).

Chondroitin Sulfate Tetrasaccharides: Synthesis, Three-Dimensional Structure and Interaction with Midkine.

The biological activity of midkine, a cytokine implicated in neuro- and tumourigenesis, is regulated by its binding to glycosaminoglycans (GAGs), such as heparin and chondroitin sulfate (CS). To better understand the molecular recognition of GAG sequences by this growth factor, the interactions between synthetic chondroitin sulfate-like tetrasaccharides and midkine were studied by using different techniques. Firstly, a synthetic approach for the preparation of CS-like oligosaccharides in the sequence GalNAc-GlcA was developed.

Mimicking Tyrosine Phosphorylation in Human Cytochrome c by the Evolved tRNA Synthetase Technique.

Phosphorylation of tyrosine 48 of cytochrome c is related to a wide range of human diseases due to the pleiotropic role of the heme-protein in cell life and death. However, the structural conformation and physicochemical properties of phosphorylated cytochrome c are difficult to study as its yield from cell extracts is very low and its kinase remains unknown. Herein, we report a high-yielding synthesis of a close mimic of phosphorylated cytochrome c, developed by optimization of the synthesis of the non-canonical amino acid p-carboxymethyl-L-phenylalanine (pCMF) and its efficient site-specific incorporation at position 48.

Structures of glycans bound to receptors from saturation transfer difference (STD) NMR spectroscopy: quantitative analysis by using CORCEMA-ST.

Glycan-receptor interactions are of fundamental relevance for a large number of biological processes, and their kinetics properties (medium/weak binding affinities) make them appropriated to be studied by ligand observed NMR techniques, among which saturation transfer difference (STD) NMR spectroscopy has been shown to be a very robust and powerful approach. The quantitative analysis of the results from a STD NMR study of a glycan-receptor interaction is essential to be able to translate the resulting spectral intensities into a 3D molecular model of the complex. This chapter describes how to carry out such a quantitative analysis by means of the Complete Relaxation and Conformational Exchange Matrix Approach for STD NMR (CORCEMA-ST), in general terms, and an example of a previous work on an antibody-glycan interaction is also shown.