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Biomedical subjects

N K Kochetkov

Publications and source records attributed to N K Kochetkov.

At least 37 records · Page 2Linked to original sources
PubMed1993

Synthesis of 2,3-di-O-glycosyl derivatives of methyl alpha- and beta-D-glucopyranoside.

The syntheses are described of 2,3-di-O-glycosyl derivatives of methyl alpha- and beta-D-glucopyranoside having alpha-D-manno-, beta-D-galacto-, alpha-L-rhamno-, alpha-L-fuco-, and beta-L-fuco-pyranosyl substituents at O-2 and O-3. The syntheses involved glycosylation of methyl 4,6-O-benzylidene-alpha- (24) and -beta-D-glucopyranoside (21), and substituted derivatives of 21 bearing 2-O-(2,3,4,6-tetra-O-benzoyl-alpha-D-mannopyranosyl)-, -(2,3,4,6-tetra-O- acetyl-beta-D-galactopyranosyl)-, -(2,3,4,-tri-O-benzoyl-alpha-L- rhamnopyranosyl)-, and -(2,3,4-tri-O-benzoyl-beta-L-fucopyranosyl) groups.

Carbohydrate Conformation↗
PubMed1993

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.

Carbohydrate Conformation↗
PubMed1993

Glycosylation by sugar 1,2-O-(1-cyanobenzylidene) derivatives: influence of glycosyl-donor structure and promoter.

3,4,6-Tri-O-acetyl-1,2-O-(1-cyanobenzylidene)-alpha-D-galactopy ranoses with differently substituted aromatic nuclei have been synthesised and used as glycosyl donors in reactions with the acceptors methyl 2,3,4-tri-O-acetyl-6-O-trityl-beta-D-galactopyranoside (11) and methyl 2,4,6-tri-O-acetyl-3-O-trityl-beta-D-galactopyranoside (12). The glycosylation of 11 gave only beta products. The effeciency and stereoselectivity of the glycosylations of 12 depend on the nature of the substituent in the aromatic ring. The stereoselectivity for the formation of 1,2-trans-glycosidic bonds was the highest with the p-methoxy-benzylidene derivative with triphenylmethylium triflate as the promoter.

Benzylidene Compounds↗
PubMed1993

Structure of the O-specific polysaccharide of Salmonella arizonae O45.

The O-specific polysaccharide of Salmonella arizonae O45 (Arizona 11) is acidic and has a branched hexasaccharide repeating unit containing two residues of L-fucose, one residue each of D-galactose, D-ribose, D-glucuronic acid, and 2-acetamido-2-deoxy-D-glucose, and an O-acetyl group. It was studied with the help of 1H and 13C NMR spectroscopy, including 1D selective spin-decoupling and homonuclear Hartmann-Hahn spectroscopy, 2D homonuclear and 13C-1H heteronuclear shift-correlated (COSY) and NOE (ROESY) spectroscopy, as well as by methylation analysis, and selective cleavages with anhydrous HF (or dilute HCl) and lithium in ethylenediamine to yield two different tetrasaccharide fragments. As a result, the following structure of the polysaccharide was established: [formula: see text] Anomalous 13C chemical shifts were observed in the spectrum of the trisaccharide fragment alpha-L-Fucp-(1-->2)-beta-D-Gal p-(1-->3)-beta-D-Glc pNAc, structurally related to the Le(d) blood-group determinant, and rationalised by inter-residue proton-proton interactions.

Acetylglucosamine↗
PubMed1993

The beta-configuration of the rhamnosidic linkage in Salmonella serogroups C2 and C3 lipopolysaccharide is important for the immunochemistry of the O-antigen 8.

Pairs of synthetic di- and trisaccharide-polyacrylamide (PAA) conjugates, isomers in configuration of the rhamnose residue and related to the sequence abequosyl-(alpha 1-3)-rhamnosyl-(beta 1-2)-mannose (ARM), found in Salmonella serogroup C2 (O-antigens 6,8) and C3 (O-antigens 8,20) lipopolysaccharides, have been used as coating antigens and inhibitors in enzyme immunoassay to evaluate the immunochemical importance of the beta-rhamnosidic linkage in the O-antigen 8. In each pair, the reaction with the factor O:6,8 serum was more pronounced for the synthetic antigen with the beta-rhamnosidic linkage. The ARM-PAA conjugate with the beta-rhamnosidic linkage was found to be 2000 fold more efficient as inhibitor of binding of the factor O:6,8 serum to the AR beta M-PAA conjugate as compared to the alpha-linked analogue. The discrepancy in immunochemical behaviour of the alpha and beta-rhamnose containing ARM oligosaccharides can be explained by conformational differences of the oligosaccharides. A slight cross-reactivity observed in the interaction of antiserum against abequosyl-(alpha 1-3)-mannose, representative of Salmonella O-antigen 4, coupled to BSA, with Salmonella O-factor 8 specific abequosyl-(alpha 1-3)-rhamnose containing conjugates is due to the common terminal immunodominant sugar, abequose.

Antibody Specificity↗
PubMed1993

Immunological studies of an artificial antigen with specificity of a common polysaccharide antigen of Pseudomonas aeruginosa.

Synthetic D-rhamnan, with the structure of Pseudomonas aeruginosa common polysaccharide antigen (CPA), was conjugated with BSA. The artificial antigen obtained, and the natural antigens, lipopolysaccharides (LPS) of P. aeruginosa and Pseudomonas cerasi with rhamnan chains of the same structure, were studied by ELISA with rabbit antibodies to the D-rhamnan-BSA conjugate and to the P. cerasi O-antigen. Immunological relations between the LPS of P. aeruginosa and P. cerasi determined by CPA as well as between these LPS and D-rhamnan-BSA were revealed by ELISA. O-antiserum to P. cerasi possesses protective activity in the mouse passive protection test when mice are challenged with some P. aeruginosa strains; the antiserum to the D-rhamnan-BSA does not possess protective activity in mice.

Animals↗
PubMed1993

[Computerized structural analysis of O-specific polysaccharides O1A, O1B, and O1C from Escherichia coli].

A computer evaluation of 13C-NMR data for the title polysaccharides based on the monosaccharide and methylation analysis data led to the structure of the repeating unit of the O1A polysaccharide as well as to several probable structures of the O1C polysaccharide, of which the correct one was inferred by means of a single NOE experiment. The analysis of the spectrum of the O1B polysaccharide was unsuccessful, due to the presence in its structure of the fragment alpha-L-Rha-(1-->2)-alpha-D-Gal-(1-->3)-D-GlcNAc with the terminal (1-->2)-linkage, whose spectral data could not be calculated by additive schemes using only glycosylation effects. However in reevaluation of the O1B spectral data by taking into account the deviations from additivities of the chemical shifts values in spectra of the related trisaccharides, to reveal the most probable structure of the O1B's repeating unit. [formula: see text]

Carbohydrate Conformation↗
PubMed1993

[Structural study of O-specific polysaccharides from Proteus mirabilis O28 and 3/6, containing amides of D-galacturonic acid with L-amino acids; C-methylation and beta-elimination at L-serine and L-threonine residues upon analysis using the methylation method].

Structures of the O-specific polysaccharides of Proteus mirabilis O28 and 3/6 were studied by partial acid hydrolysis followed by borohydride reduction and methylation and GLC/MS analysis of the resulting glycosyl alditol derivatives. C-Methylation and beta-elimination in serine and threonine attached to the carboxyl group of galacturonic acid were observed in the course of the methylation analysis.

Amino Acids↗
PubMed1993

[Structural and immunologic studies of Proteus mirabilis 033 O-specific polysaccharide].

O-specific polysaccharide was obtained by mild acid degradation of P. mirabilis 033 lipopolysaccharide (LPS). It was found to contain N-acetyl-D-glucosamine, D-glucuronic acid and N-acetyl-L-fucosamine in a ratio 1:1:1. On the basis of the data obtained from 13C-NMR and methylation analysis, the following structure of repeating unit was established: [formula: see text] Selective removal of the D-GlcA significantly decreased reactivity of 033 O-specific polysaccharide with homologous antiserum. This component was plays an immunodominant role. Cross reactivity between anti-033 serum and disaccharide alfa-L-FucNAc-beta-D-GlcNAc containing P. vulgaris 023 and S. arizonae 059 O-specific polysaccharides was also observed.

Antigens, Bacterial↗
PubMed1993

[Structure of lipopolysaccharides from gram-negative bacteria. I. Common characteristics of lipopolysaccharides and lipid A structure (Review)].

The data on the structure and properties of outer membrane lipopolysaccharides of gram-negative bacteria are reviewed with special reference to the general organization of the lipopolysaccharide molecule and the structure of the lipid moiety (lipid A). The correlation between the structure of the lipopolysaccharides and lipid A and their biological properties and functions are discussed.

Carbohydrate Conformation↗
PubMed1993

[Structure of lipopolysaccharides from gram-negative bacteria. II. Core structure (Review)].

The review summarizes the data on the core structure of bacterial lipopolysaccharides (LPS) which represents an oligosaccharide binding the lipid moiety of the macromolecule to the O-antigenic polysaccharide chain. Both S-strains with complete LPS and R-mutants having various defects of the core biosynthesis are considered. The role of the core in the outer membrane functioning and manifestation of antigenic specificity of LPS is discussed.

Carbohydrate Conformation↗
PubMed1992

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.

Carbohydrate Sequence↗
PubMed1992

Synthesis of a heteroglycuronan derivative containing the beta-D-galactopyranosyluronic acid (1-->3)-L-rhamnose repeating unit.

Helferich glycosylation of the cyanoethylidene L-rhamnose derivative 3 with the galactosyluronic bromide 2 gave the disaccharide 4 as a key intermediate in the synthesis of the monomer 13 for trityl-cyanoethylidene condensation (TCC). The following formation of the monomer 13, including introduction of a trityl group at O-3', proceeded in six steps. Because of the difficulty of some steps, an alternative route for 13 was tested. Model compounds 20, 21, and 22 were synthesized in order to confirm the stereoregularity of the products of the polycondensation. The polycondensation of the monomer gave D-GalpA-(1-->3)-L-Rha-oligomer derivatives consisting mainly of three repeating units. This result is in contrast with the degree of polymerisation (dp > or = 22) of other synthetic rhamnans, but is very similar to dp 2-7 of homo- and hetero-glucuronan derivatives.

Carbohydrate Sequence↗