D. E. Tsvetkov

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 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.

Neoglycoconjugates Based on Dendrimer Poly(aminoamides)

Neoglycoconjugates containing 4, 8, 32, and 64 terminal residues of B-disaccharide (BDI) or N-acetylneuraminic acid (Neu5Ac) attached to poly(aminoamide)-type dendrimers (PAMAMs) were synthesized. The ability of BDI conjugates to bind natural xenoantibodies (anti-BDI antibodies) and the ability of Neu5Ac conjugates to inhibit the hemagglutinin-mediated adhesion of influenza virus were studied. The biological activity of PAMAM conjugates turned out to be higher than that of free carbohydrate ligands, but less than that of multivalent glycoconjugates based on other types of synthetic polymeric carriers. A conformational analysis of PAMAM matrices and resulting conjugates was performed to determine the statistical distances between carbohydrate ligands. The computations revealed the tendency of the PAMAM chains toward compaction and formation of dense globules. The process results in a decrease in the distances between the carbohydrate ligands in the conjugates and, hence, could affect the ability of glycoconjugates to efficiently bind the polyvalent carbohydrate-recognizing proteins.

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.

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.

Analysis of content of (–)-secoisolariciresinol and related polyphenols in different morphological parts and anatomical structures of larch wood from Siberia

Productive efficiency of technology of polysaccharide and lignin manufacturing from wood raw materials can be significantly improved by integration of purification stages of low molecular weight wood components widely used in applied chemistry into the technological cycle. In this connection, phenols including lignans and flavonoids, which have a practical application potential, are of a special interest. In the present work the results of a study of the content of (–)-secoisolariciresinol, dihydroquercetin and related polyphenols in different morphological parts and anatomical structures of larch wood from the Siberia are analyzed. Analysis of the content of the listed products by reversed-phase HPLC provides the selection of optimal raw material for organizing the manufacture of the listed compounds with predictable efficiency. Increased content of (–)-secoisolariciresinol (up to 3—4%) observed in wood of the trunk knot areas of larch from Khakassia evidences the prospects of raw material processing in this region for production of (–)-secoisolariciresinol from the wastes of larch wood refinery.

In vitro effect of Knotolan, a new lignan from Abies sibirica, on the growth of hormone-dependent breast cancer cells.

Here we present antiestrogenic effects of Knotolan®, a new dietary lignan from Abies sibirica raw material. Knotolan abolished growth-stimulating effects of 17β-estragiol on hormonedependent MCF-7 cells.

Separation of levoglucosan supramers by high performance liquid chromatography

Analysis of levoglucosan by ligand-exchange chromatography with UV detection showed deviations from the Bouguer—Lambert—Beer law. Their character allowed us to suggest that the deviations are caused by the formation of levoglucosan supramers in the eluent.

Polyphenolicic compounds in the extracts of the birch Betula pendula knotwood

Four polyphenolic compounds were isolated from the extracts of the birch Betula pendula knotwood, purified by HPLC and identified by NMR spectroscopy and mass spectrometry. Three compounds were found to be arylheptanoids, two of them being related to the known carpinontriol and casuarinondiol and one being earlier unknown.

Estimation of the degree of conjugation of oligosaccharide haptens to bovine serum albumin in the course of the squarate procedure using gel permeation HPLC

An approach to estimate the degree of conjugation of oligosaccharide haptens to bovine serum albumin by the squarate procedure was proposed. The approach includes gel permeation HPLC in combination with the multichannel detection.