Elena A. Khatuntseva

A study of fucoidan from the brown seaweed Chorda filum

Fucoidan fractions from the brown seaweed Chorda filum were studied using solvolytic desulfation. Methylation analysis and NMR spectroscopy were applied for native and desulfated polysaccharides. Homofucan sulfate from C. filum was shown to contain poly-alpha-(1-->3)-fucopyranoside backbone with a high degree of branching, mainly of alpha-(1-->2)-linked single units. Some fucopyranose residues are sulfated at O-4 (mainly) and O-2 positions. Some alpha-(1-->3)-linked fucose residues were shown by NMR to be 2-O-acetylated. The 1H and 13C NMR spectra of desulfated, deacetylated fucan were completely assigned. The spectral data obtained correspond to a quasiregular polysaccharide structure with a branched hexasaccharide repeating unit. Other fucoidan fractions from C. filum have more complex carbohydrate composition and give rather complex methylation patterns. [formula: see text]

Synthesis and Molecular Recognition Studies of the HNK-1 Trisaccharide and Related Oligosaccharides. The Specificity of Monoclonal Anti-HNK-1 Antibodies as Assessed by Surface Plasmon Resonance and STD NMR

The human natural killer cell carbohydrate, HNK-1, plays function-conducive roles in peripheral nerve regeneration and synaptic plasticity. It is also the target of autoantibodies in polyneuropathies. It is thus important to synthesize structurally related HNK-1 carbohydrates for optimizing its function-conducive roles, and for diagnosis and neutralization of autoantibodies in the fatal Guillain-Barré syndrome. As a first step toward these goals, we have synthesized several HNK-1 carbohydrate derivatives to assess the specificity of monoclonal HNK-1 antibodies from rodents: 2-aminoethyl glycosides of selectively O-sulfated trisaccharide corresponding to the HNK-1 antigen, its nonsulfated analogue, and modified structures containing 3-O-fucosyl or 6-O-sulfo substituents in the N-acetylglucosamine residues. These were converted, together with several related oligosaccharides, into biotin-tagged probes to analyze the precise carbohydrate specificity of two anti-HNK-1 antibodies by surface plasmon resonance that revealed a crucial role of the glucuronic acid in antibody binding. The contribution of the different oligosaccharide moieties in the interaction was shown by saturation transfer difference (STD) NMR of the complex consisting of the HNK-1 pentasaccharide and the HNK-1 412 antibody.

SYNTHESIS, NMR, AND CONFORMATIONAL STUDIES OF FUCOIDAN FRAGMENTS. III.[1] EFFECT OF BENZOYL GROUP AT O-3 ON STEREOSELECTIVITY OF GLYCOSYLATION BY 3-O- AND 3,4-DI-O-BENZOYLATED 2-O-BENZYLFUCOSYL BROMIDES

The effect of a benzoyl group at O-3 on stereoselectivity of glycosylation by 3-O- and 3,4-di-O-benzoylated 2-O-benzyl-L-fucopyranosyl bromides was studied by direct chemical experiments and computational chemistry. The influence of a benzoyl group at O-3 of the fucosyl donors was shown to have a larger effect on the efficiency of α-fucosylation than a benzoyl group at O-4. It is hypothesized that this is a result of the ability of a benzoyl group at O-3 to participate in glycosyl cation stabilization.

Synthesis, NMR and Conformational Studies of Fucoidan Fragments 1:1 Desulfated 2,3- and 3,4-Branched Trisaccharide Fragments and Constituting Disaccharides

ABSTRACT Two fucotriosides with vicinal disubstitution α-L-Fuc-(1→2)[α-L-Fuc-(1→3)]α-L-Fuc-OPr (1) and α-L-Fuc-(1→3)[α-L-Fuc-(1→4)]α-L-Fuc-OPr (2), which are related to fragments of natural polysaccharides fucoidans, have been synthesized together with constituent disaccharides 3-5. Spectral and conformational properties of tri- and disaccharides have been investigated by 1H, 13C and NOE NMR spectroscopy.

SYNTHESIS, NMR, AND CONFORMATIONAL STUDIES OF FUCOIDAN FRAGMENTS 4[1]: 4-MONO- AND 4,4′-DISULFATED (1→3)-α-l-FUCOBIOSIDE AND 4-SULFATED FUCOSIDE FRAGMENTS

Propyl 4-O-sulfonato- and 4,4′-di-O-sulfonato-3-O-α-l-fucopyranosyl-α-l-fucopyranosides, which are related to fragments of brown algal fucoidans, have been synthesized. Their spectral (1H and 13C NMR, NOE) and conformational properties have been studied in combination with molecular modeling and compared with the respective non-sulfated propyl fucobioside. Correlations between chemical shifts and conformational properties of these compounds were investigated.

Synthesis, NMR and Conformational Studies of Fucoidan Fragments. V.[1] Linear 4,4′,4″‐Tri‐O‐Sulfated and Parent Non‐sulfated (1→3)‐Fucotrioside Fragments

Propyl 4,4′,4″‐tri‐O‐sulfated and non‐sulfated (1→3)‐α‐l‐fucotriosides which are related to fragments of natural fucoidans have been synthesized. Their spectral and conformational properties have been investigated by 1H and 13C NMR, NOE and molecular modeling. Molecular mechanics calculations of the tri‐O‐sulfated compound as a trianion did not give agreement with the experimental NOE values, while the model with the non‐dissociated sulfo group on the non‐reducing end worked successfully. (1→3)‐Fucobioside fragments in both trisaccharides investigated were shown to have the same range of conformations as in previously described propyl (1→3)‐α‐l‐fucobiosides, but with the increase of the relative population of the conformer with the spatial proximity of H‐1′ and H‐4 in the case of non‐sulfated fucotrioside.

Synthesis, NMR, and Conformational Studies of Fucoidan Fragments. VII.1 Influence of Length and 2,3‐Branching on the Conformational Behavior of Linear (1→3)‐Linked Oligofucoside Chains

The conformational behavior of linear (1→3)‐linked propyl di‐, tri‐, tetrafucosides and 2,3‐branched tetrafucosides with linear (1→3)‐linked trisaccharide backbone related to fragments of natural fucoidans were studied by theoretical molecular modeling and experimental determination of transglycosidic vicinal coupling constants 3JC,H. The application of NOE NMR‐spectroscopy, which is traditionally used in conformational analysis of oligosaccharides, was accompanied by experimental difficulties in the case of tetrafucosides, due to the overlap of cross‐peaks and their trend to be close to zero. It was shown that conformations of difucoside units in the studied compounds depend on their position within the oligosaccharide backbone, on the chain length, and on the presence or absence of 2,3‐branch point. The comparison of experimental and calculated values of transglycosidic constants 3JC,H showed good coincidence for the middle disaccharide units of tetrafucosides, indicating that these units are more rigid than terminal ones.

Synthesis and structural studies of branched 2-linked trisaccharides related to blood group determinants

A series of trisaccharide glycosides, Fuc-(1 reversible 2)-beta-Gal-(1 reversible 3)-beta-X-OMe (X = GlcNAc, Glc, 2-deoxy-Glc) related to the blood group determinant Le(d) have been synthesised both as their alpha- and beta-Fuc anomers together with the component disaccharide starting compounds. The conformational properties of the six trisaccharides together with their parent disaccharides have been investigated by NMR spectroscopy (proton and carbon chemical shifts and proton NOEs) in combination with computer modeling using the Monte Carlo approach and the HSEA force field using the GEGOP programme. The interaction between the terminal fucose unit and the reducing unit was probed by substitution of bulky NAc group with hydroxyl and deoxy substituents, respectively. Compounds with severe steric interactions were identified by the non-additivity of their carbon chemical shifts. This was subsequently confirmed by the detailed conformational assessment by NOE spectroscopy and computer modeling. The most severe contacts arose in the alpha-L-Fuc derivatives, whereas the beta-linked L-Fuc derivatives only in one case exhibit severe steric interaction as probed by the NMR parameters.

Synthetic β-(1→3)-d-glucooligosaccharides: model compounds for the mechanistic study of β-(1→3)-d-glucan bioactivities and design of antifungal vaccines

Synthetic methods used for the preparation of linear β-(1→3)-d-glucooligosaccharides with three and more monosaccharide units and their conjugates with carrier proteins, as well as the application of such derivatives in the mechanistic study of bioactivites of natural β-(1→3)-d-glucans and in the design of conjugated antifungal vaccines are considered.

The Synthesis and NMR and Conformational Studies of Fucoidan Fragments: VI.1 Fragments with an α-(1 → 2)-Linked Fucobioside Unit

A series of selectively sulfated di- and trisaccharide derivatives corresponding to the potential fragments of fucoidans with a α-(1 → 2)-linked fucobioside unit were synthesized and studied by 1Н and 13C NMR spectroscopy. NOE experiments and molecular modeling were used for a conformational analysis of the compounds synthesized. In the case of disaccharides, the experimental NOE values were found to agree with those obtained using modeling with the use of density functional theory (DFT) and differ from those resulting from modeling by the molecular mechanics MM3 force field. Trisaccharide fragments partially or completely sulfated in position 4 turned out to be correctly described by both MM3 force field and DFT computation.