N. E. Byramova

Synthesis of polymeric neoglycoconjugates based on N-substituted polyacrylamides

Several types of polymeric glycoconjugates,N-substituted polyacrylamides, have been synthesized by the reaction of activated polymers with ω-aminoalkylglycosides: (i) (carbohydrate-spacer)n-polyacrylamide, ‘pseudopolysaccharides’; (ii) (carbohydrate-spacer)n-phosphatidylethanolaminem-polyacrylamide, neoglycolipids, derivatives of phosphatidylethanolamine; (iii) (carbohydrate-spacer)n-biotinm-polyacrylamide, biotinylated probes; (iv) (carbohydrate-spacer)n-polyacrylamide-(macroporous glass), affinity sorbents based on macroporous glass, covalently coated with polyacrylamide. An almost quantitative yield in the conjugation reaction makes it possible to insert in the conjugate a predetermined quantity of the ligand(s).Pseudopolysaccharides proved to be a suitable form of antigen for activation of polystyrene and poly(vinyl chloride) plates (ELISA) and nitrocellulose membranes (dot blot), being advantageous over traditional neoglycoproteins. Polyvalent glycolipids insert well in biological membranes: their physical properties, particularly solubility, can be changed in a desired direction. Biotinylated derivatives were used as probes for detection and analysis of lectins.

Synthetic polymeric sialoside inhibitors of influenza virus receptor-binding activity

Anomeric aminobenzylglycosides of Neu5Ac were coupled with the polyacrylate carrier and a number of synthetic polyvalent sialosides obtained were investigated as inhibitors of influenza virus attachment. The inhibitory activity of polymeric sialosides is highly dependent upon the Neu5Ac residue content and the nature of the carrier. The polyacrylic acid based polymer bearing 10 mol% of Neu5Ac is 3 orders of magnitude more potent inhibitor than the corresponding monovalent benzylsialoside and considerably more active than fetuin.

Synthetic polymeric inhibitors of influenza virus receptor-binding activity suppress virus replication.

A new approach to anti-influenza chemotherapy is based on the development of synthetic inhibitors of virus attachment to host cells. These inhibitors are prepared by anchoring the minimum receptor determinant of influenza virus, sialic acid, to polymeric or liposomal carriers. In this study, a series of poly(acrylic acid-co-acrylamides) and dextrans bearing pendant glycylamidobenzylsialoside groups were synthesized and evaluated for their binding to a panel of influenza A and B virus strains and for their ability to inhibit virus infectivity in cell culture. Significant type-, subtype-, and strain-specific variation in virus susceptibility to the synthetic inhibitors was observed. Among the viruses tested, H3 subtype strains evolved in humans since 1975 were the most sensitive, while the earlier H3 viruses and the type B strains were resistant. The virus-inhibitory potency of the polymeric sialosides correlated with their bindings to the virus, and was dependent on the virus affinity for the ligand, the density of the ligand, and the nature and molecular mass of the polymeric carrier. In embryonated eggs, the antiviral effect of poly(acryloyl-glycylamidobenzylsialoside-co-acrylic acid) was comparable to that of equine alpha 2-macroglobulin.

Synthesis of Sialic Acid Pseudopolysaccharides by Coupling of Spacer-Connected Neu5Ac With Activated Polymer

ABSTRACT A new approach to the synthesis of polyvalent sialosides (pseudopolysaccharides) of Neu5Ac is described. Two monovalent sialosides, namely 4-acetamido- and 4-glycylamidobenzyl α-glycosides of Neu5Ac (and their β-anomers) have been synthesized. The latter, each having a free amino group, have been coupled with poly(4-nitrophenylacrylate) followed by treatment with sodium hydroxide or ethanolamine to give water soluble polyvalent sialosides differing in the nature of polymeric backbone. The coupling proceeded quantitatively providing polymers with a desired number of spacer-connected Neu5Ac residues attached. The polymers are shown to have considerable activity as inhibitors of influenza virus adhesion.

A simple procedure for the synthesis of the methyl and benzyl glycosides of Neu5Ac and 4-epi-Neu5Ac. Conversion of the benzyl and methyl glycosides of Neu5Ac into N-trifluoroacetylneuraminic acid benzyl glycosides*

Abstract From the reaction products of the Kuhn-Bashang synthesis of Neu5Ac, 5-acetamido-3,5-dideoxy- α -and - β - d - glycero - d - talo -2-nonulopyranosonic acid (4- epi -Neu5Ac) were isolated as the acetylated methyl esters ( 1 and 2 ). Treatment of methyl (5-acetamido-4,7,8,9-tetra- O -acetyl-3,5-dideoxy- d - glycero - d - galacto -2-nonulopyranosyl bromide)onate ( 5 ) with an excess of methanol gave a high yield of a 9:1 α,β -mixture of the methyl glycosides ( 13 and 14 ). Likewise, with benzyl alcohol, 5 gave a 63:32 α,β -mixture of the benzyl glycosides ( 17 and 18 ). Treatment of methyl (5-acetamido-4,7,8,9-tetra- O -acetyl-3,5-dideoxy- β - d - glycero -pd- talo -2-nonulopyranosyl bromide)onate ( 7 ) with an excess of benzyl alcohol gave a 3:1 α,β -mixture of the benzyl glycosides ( 21 and 22 ) together with methyl 5-acetamido-4,7,8,9-tetra- O -acetyl-2,6-anhydro-3,5-dideoxy- d - glycero - d - talo -non-2-enonate ( 9 ). Condensation of bromide 7 in chloroform with benzyl alcohol in the presence of silver carbonate afforded a 7:1 α,β -mixture of benzyl glycosides together with 9 . The benzyl glycosides 17 and 18 were converted into their respective N -trifluoroacetyl derivatives 27 and 28 by saponification and then N -trifluoroacetylation. Methanolysis of Neu5Ac followed by N -trifluoroacetylation and O -acetylation afforded methyl (methyl 4,7,8,9-tetra- O -acetyl-3,5-dideoxy-5-trifluoroacetamido- β - d - glycero - d - galacto -2-nonulopyrano-sid)onate ( 30 ), which was converted into the benzyl glycosides ( 32 and 33 ) via the 2-bromide ( 31 ). A simplified preparation of the protected 2-halogeno derivatives of Neu5Ac and 4- epi -Neu5Ac is described. The conversion of neuraminic acid methyl glycoside into the corresponding 2-bromide derivative by the action of hydrogen bromide is demonstrated.

Detection of Sialic Acid Residues and Studies of Their Organization in Normal and Tumor α1-Acid Glycoproteins as Probed by Surface-Enhanced Raman Spectroscopy

Surface-enhanced Raman scattering (SERS) spectra of sialic acid (SA) benzyl, and methyl glycosides as well as natural sialylated glycoproteins from human cells of healthy donors and tumor patients have been analyzed in view of the fact that peripheral fragments of many bioactive glycoconjugates are SA residues. SA residues can be detected by SERS at concentrations as low as 10−6 M. The pattern of interaction of SA with the surface of a silver hydrosol involves the C-8 and C-9 hydroxy groups of SA. SERS spectroscopy is sensitive to changes in the content and type of branching of sialylated sugar chains in sialylglycoproteins. The differences in sialylated sugar-chain organization for α1-acid glycoproteins from healthy donors and tumor patients have been detected by means of SERS spectroscopy. The first example of the detection of SA residues for a suspension of living cells has been presented.

Monovalent and polymeric 5N-thioacetamido sialosides as tightly-bound receptor analogs of influenza viruses.

A possible approach to the development of synthetic inhibitors of influenza virus attachment to host cells is based on the anchoring of the minimum receptor determinant of influenza virus, sialic acid, to a polymeric carrier. In this study, the effect of substitution of oxygen by sulphur in the 5N-acetyl moiety of sialic acid on the binding of monovalent and polymeric sialosides by A and B influenza virus strains was investigated. The polymeric inhibitor with pendant 5N-thioacetylneuraminic acid residues was found to be more broadly active against different virus stains that the one prepared from the Neu5Ac ligand.

1,6-anhydro-N-acetyl-β-D-glucosamine in oligosaccharide synthesis: II. The synthesis of the spacered Ley tetrasaccharide

Abstract3-Aminopropyl glycoside of 3,2′-di-O-α-L-fucosyl-N-acetyllactosamine (Ley tetrasaccharide) was synthesized. The glycosyl donor, 2-O-acetyl-2,4,6-tri-O-benzoyl-α-D-galactopyranosyl bromide, was coupled with glycosyl acceptor, 1,6-anhydro-2-acetamido-2-deoxy-β-D-glucopyranose or its 3-O-acetyl derivative, to give the corresponding N-acetyllactosamine derivatives in 20 and 71% yields, respectively. The glycosyl donor was synthesized from 1,2-di-O-acetyl-3,4,6-triO-benzoyl-D-galactopyranose, which was obtained by the treatment of benzobromogalactose with sodium borohydride to yield 1,2-O-benzylidene derivative and subsequent removal of benzylidene group and acetylation. Acidic methanolysis of the disaccharide derivatives resulted in the selective removal of one or both acetyl groups to give the disaccharide acceptor bearing hydroxy groups at C3 of the glucosamine residue and C2 of the galactose residue. The introduction of fucose residues in these positions by the treatment with tetrabenzylfucopyranosyl bromide resulted in a tetrasaccharide derivative, which was converted into 3,2′-di-O-α-L-fucopuranosyl-1,6-anhydro-N-acetyllactosamine peracetate after substitution of acetyl groups for benzoyl and benzyl groups. Opening of the anhydro ring by acetolysis resulted in peracetate, which was then converted into the corresponding oxazoline derivative by two steps. Glycosydation of the oxazoline derivative with 3-trifluoroacetamidopropan-1-ol and removal of O-acetyl and N-trifluoroacetyl protective groups resulted in a free spacered Ley tetrasaccharide.

1,6-Anhydro-N-acetyl-β-D-glucosamine in the oligosaccharide syntheses: I. Synthesis of 3-acetate and 3-benzoate of 1,6-anhydro-N-acetyl-β-D-glucosamine via the 4-O-trityl derivative

Abstract3-O-Acetyl and 3-O-benzoyl derivatives of 1,6-anhydro-N-acetyl-β-D-glucosamine were synthesized via its selective tritylation followed by the 3-O-acylation and removal of the trityl protective group. Tritylium trifluoromethanesulfonate, which can easily be prepared by mixing solutions of triphenylcarbinol and trimethylsilyl trifluoromethanesulfonate in an equimolar ratio, was suggested as a reagent for the effective tritylation of a secondary hydroxyl group.

Synthesis of disaccharide neu5Gcα(2–6)galNAcα as a spacer glycoside

The first synthesis of the Neu5Gc analogue of SiaTn disaccharide, which can be detected in breast tumors by immunochemical methods, is reported. The regioselective sialylation of (3-trifluoroacetamidopropyl)-2-azido-2-deoxy-α-D-galactopyranoside with peracetate of the methyl ester ofN-acetoxyacetyl-neuraminic acid β-ethylthioglycoside in the presence ofN-iodosuccinimide and trifluoromethanesulfonic acid (or its trimethylsilyl ester) resulted in the derivatives of α- and β-sialyl(2→6)galactosaminide in 39 and 32% yields, respectively. The catalytic hydrogenolysis of the azido group and subsequentN- andO-acetylation of the α-anomer gave the peracetate of trifluoroacetamidopropyl glycoside. Removal of the protective groups led to glycoside Neu5Gcα2→6GalNAcα-O(CH2)3NH2. Using the Neu5Gc derivative with acetoxyacetyl groups at positions O9 and O4 as a donor increases the α-selectivity of sialylation to afford the α- and β-anomers in 69 and 8% yields, respectively.