Nikolay E. Nifant'ev

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, 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 of Neu5Ac- and Neu5Gc-α-(2→6′)-lactosamine 3-aminopropyl glycosides

Abstract In order to prepare 3-aminopropyl glycosides of Neu5Ac-α-(2→6′)-lactosamine trisaccharide 1 , and its N -glycolyl containing analogue Neu5Gc-α-(2→6′)-lactosamine 2 , a series of lactosamine acceptors with two, three, and four free OH groups in the galactose residue was studied in glycosylations with a conventional sialyl donor phenyl [methyl 5-acetamido-4,7,8,9-tetra- O -acetyl-3,5-dideoxy-2-thio- d - glycero -α- and β- d - galacto -2-nonulopyranosid]onates ( 3 ) and a new donor phenyl [methyl 4,7,8,9-tetra- O -acetyl-5-( N - tert -butoxycarbonylacetamido)-3,5-dideoxy-2-thio- d - glycero -α- and β- d - galacto -2-nonulopyranosid]onates ( 4 ), respectively. The lactosamine 4′,6′-diol acceptor was found to be the most efficient in glycosylation with both 3 and 4 , while imide-type donor 4 gave slightly higher yields with all acceptors, and isolation of the reaction products was more convenient. In the trisaccharides, obtained by glycosylation with donor 4 , the 5-( N - tert -butoxycarbonylacetamido) moiety in the neuraminic acid could be efficiently transformed into the desired N -glycolyl fragment, indicating that such protected oligosaccharide derivatives are valuable precursors of sialo-oligosaccharides containing N -modified analogues of Neu5Ac.

Synthesis of 3-O-sulfoglucuronyl lacto-N-neotetraose 2-aminoethyl glycoside and biotinylated neoglycoconjugates thereof ☆

The 2-aminoethyl glycoside of pentasaccharide 3-O-sulfo-GlcA(beta-1-->3)Gal(beta-1-->4)GlcNAc(beta-1-->3)Gal(beta-1--> 4)Glc(beta (1) and its conjugates with biotin and biotinylated polyacrylic acid were synthesized as molecular probes to investigate the recognition of the HNK-1 epitope containing carbohydrates by proteins. Key steps in the first of two investigated schemes for the preparation of the target compound 1 were (a) assembling of the pentasaccharide backbone (compound 10) by glycosylation of selectively substituted allyl glycoside of the trisaccharide GlcNAc(beta-1-->3)Gal(beta-1-->4)Glc(beta with glucuronyl-galactose glycosyl donor, (b) transformation of the allyl aglycon in 10 into 2-azidoethyl one (to give 11), (c) selective deprotection of the OH group at C-3 of the GlcA residue in 11 via saponification, intramolecular formation of 6,3-lacton (13) and its methanolysis, and (d) subsequent O-sulfation. The alternative scheme with the use of 2-azido-ethyl glycoside of the trisaccharide GlcNAc(beta-1-->3)Gal(beta-1-->4)Glc(beta instead of the allyl glycoside 6 was less effective due to smaller yield at the step of pentasaccharide synthesis. Additionally to 1 the 2-aminoethyl glycosides of the oligosaccharides GlcA(beta-1-->3)Gal(beta-1-->4)GlcNAc(beta-1-->3)Gal(beta-1-->4)Glc(beta, 3-O-sulfo-GlcA(beta-1-->3)Gal(beta, and GlcA(beta-1-->3)Gal(beta were also synthesized.

Computer-assisted analysis of the structure of regular branched polysaccharides containing 2,3-disubstituted rhamnopyranose and mannopyranose residues on the basis of 13C NMR data

A computer-assisted approach to the analysis of the structure of branched polysaccharides that contain 2,3-di-O-glycosylated alpha-rhamnopyranose and alpha-mannopyranose residues is based on evaluation of the 13C NMR spectra, using glycosylation effects and their deviations from additivity (delta delta values) at the branch points. This approach, in combination with monosaccharide and methylation analysis data, has been verified on a series of bacterial polysaccharides of known structure.

N.m.r. and conformational analysis of some 2,3-disubstituted methyl α-l-rhamnopyranosides

Abstract Conformational studies of the branched trisaccharide glycosides X-(1 → 2)[Y-(1 → 3)]-α- l -Rha-OMe (where X and Y are residues of α- l -, β- l -, α- d -, and β- d -hexopyranoses) were based on 1 H- and 13 C-n.m.r. data (n.O.e.s, 13 C chemical shifts) and theoretical calculations. In the majority of the trisaccharide glycosides, there is insignificant restriction of rotation around the glycosidic linkages in the disaccharide units as compared to the corresponding disaccharide glycosides X-(1 → 2)-α- l -Rha-OMe and Y-(1 → 3)-α- l -Rha-OMe. Differences in the conformations observed for several compounds resulted in changes of the n.O.e. patterns and in deviations from additivity of glycosylation effects in the 13 C-n.m.r. spectra.

Selectin Receptors 4: Synthesis of Tetrasaccharides Sialyl Lewis A and Sialyl Lewis X Containing A Spacer Group1,2

ABSTRACT Synthesis of two isomeric tetrasaccharides, namely Neu5Acα(2→3)Galβ(1→3)[Fucα(1→4)GlcNAcβ (sLea) and Neu5Acα(2→3)Galβ(1→4)[Fucα(1→3)]GlcNAcβ (sLex) as 3-aminopropyl glycosides is described. Preparation of these compounds was performed by sialylation of selectively protected trisaccharides Lea and Lex which contain three unsubstituted OH groups at positions 2, 3 and 4 of Gal residue. Glycosylation of Lex trisaccharide with ethylthio sialoside under promotion by NIS and TfOH in acetonitrile was effective and regio- and stereoselective to give sLex derivative in 81% yield. In contrast, sialylation of the Lca acceptor was accompanied by a variety of undesirable by-processes, namely. N-thioethylation of the GlcNAc residue, β-sialylation, and lactonisation. In order to improve the yield of sLca tetrasaccharide the glycosylation of Lea acceptor by sialyl donors of ethyl and phenyl thioglycoside (promoted by NIS-TfOH or NBS-Bu4NBr), xanthate (promotion by NIS-TfOH mixture or MeOTf) and phosphite (promote...

Binding Sites for Lewis Antigens Are Expressed by Human Colon Cancer Cells and Negatively Affect Their Migration

In colon cancer, endothelial cell selectins can promote tumor cell attachment via interactions with sialylated Lewis antigens present at the surface of tumor cells, thereby facilitating tumor cell arrest and transmigration into the extravascular space. However, it is not known whether Lewis antigens interact with colon tumor cells and modify their migration. Our aim was to detect the presence of binding sites on human tumor cells for Lewisa/x antigens and their sialylated derivatives in vitro and in vivo and to analyze their influence on migration of colon cancer cells. The immunocytochemical and histochemical levels of expression of the four Lewis antigens were quantitatively determined in four human colon cancer cell lines and in in vivo nude mice xenografts. The levels of expression of specific binding sites for these sugar epitopes were determined by synthetic neoglycoconjugates. The influence of binding of these carbohydrate ligands on cancer cell migration was quantitatively evaluated by computer-assisted phase-contrast videomicroscopy performed on Matrigel culture supports either left uncoated or coated with neoglycoconjugate presenting synthetic Lewisa, sialyl Lewisa, Lewisx, or sialyl Lewisx antigens. The influence of the calcium concentration in the culture medium on the Lewis antigen–mediated effects was checked. Human colon cancer cells expressed significant amounts of specific binding sites detected by the synthetic probes in addition to the oligosaccharide epitopes. The expression levels differed considerably between the four cell lines and between in vitro and in vivo specimens. Cell migration analysis revealed that the four Lewis antigens markedly decreased the levels of migration of the HCT-15 and LoVo cancer cells. This effect depends on the calcium concentration in the culture medium. Binding sites for Lewis epitopes are present on colon cancer cells. The functional relevance of these sites is indicated by the negative influence on cell migration of a matrix containing the oligosaccharides as ligand parts.

Studies of O-specific polysaccharide chains of Pseudomonas solanacearum lipopolysaccharides consisting of structurally different repeating units

The structures of the O-antigenic polysaccharide chains of lipopolysaccharides of a number of Pseudomonas solanacearum strains were elucidated mainly with the help of methylation analysis and 13C NMR spectroscopy, including a computer-assisted 13C NMR-based analysis. Six structurally distinct but related polysaccharides were identified. They have a backbone which is built up of three L-rhamnopyranosyl residues and one 2-acetamido-2-deoxy-D-glucopyranosyl residue, and is unsubstituted or substituted with a residue of L-xylopyranose or L-rhamnopyranose as a monosaccharide side chain. The lipopolysaccharides of most of the strains contain polysaccharide chains consisting of at least two structurally different types of repeating units. Three of the polysaccharides are common to more than one strain.

Synthesis of derivatives of 2-amino-2-deoxy-4-O-(α- and β-d-galactopyranosyl)-d-glucose

Abstract Galactosylation of methyl 6-O-acetyl-3-O-benzoyl-2-deoxy-2-phthalimido-β- d -glucopyranoside (5) and its trityl ether 9 with 2,3,4,6-tetra-O-benzoyl-α- d -galactopyranosyl bromide (8), 1-O-acetyl-2,3,4,6-tetra-O-benzoyl-β- d -galactopyranose (13), 3,4,6-tri-O-benzoyl-1,2-O-(α-p-tolythiobenzylidene)-α- d -galactopyranose (11), and 3,4,6-tri-O-benzoyl-1,2-O-(α-cyanobenzylidene)-α- d -galactopyranose (12) gave 1,2-cis- and 1,2-trans-linked disaccharide derivatives in ratios ranging from 3.8:1 to 1:8.5 depending on the conditions of glycosylation. A practical synthesis of the target lactosamine derivative 2 was achieved by the reaction of 5 and 8 in nitromethane in the presence of silver triflate.