Improved synthesis of α-L-Fuc(1→4)-β-D-GlcNAc and α-L-Fuc(1→6)-β-D-GlcNAc building blocks: A convergent strategy employing 4-O→6-O acetyl migration; NOE data of the protected α-1,4-linked disaccharide

Synthesis of β-(1→6)-linked N-acetyl-D-glucosamine oligosaccharide substrates and their hydrolysis by Dispersin B

Dispersin B (DspB) from Aggregatibacter actinomycetemcomitans is a β-hexosaminidase exhibiting biofilm detachment activity. A series of β-(1→6)-linked N-acetyl-D-glucosamine thiophenyl glycosides with degree of polymerisation (DP) of 2, 3, 4 and 5 were synthesized, and substrate specificity of DspB was studied on the obtained oligosaccharides. For oligomer synthesis a 1+2, 2+2, 1+4 coupling strategy was applied, using bromo-sugars as glycosyl donors. The formation of 1,2-trans interglycosidic bond has been ensured by 2-phtalimido protecting group; chloroacetyl group was installed to mask temporarily the 6-hydroxyl and acetate esters were applied as permanent protecting groups. Enzymatic studies revealed that DP of the GlcNAc oligomers strongly affected the hydrolysis rate, and the hydrolytic activity of DspB on the tetramer and pentamer have been found to be approximately 10-fold higher than that of the dimer. This fact indicates that four units are required for a strong binding at the active centre of DspB. The role of aromatic amino acids W237, Y187 and Y278 in substrate specificity and catalysis was also examined using mutant enzymes.

The study of the reaction of terminated oligomerization in the synthesis of oligo-(β1-6)-glucosamines

The applicability of terminated oligomerization to the synthesis of oligo-(beta1-6)-glycosamines, fragments of the intercellular polysaccharide adhesin of staphylococci, was studied. The reactions of terminated oligomerization were carried out with mono-, di-, and trisaccharide monomers and N-protected aminopropanol; and spacered mono- and disaccharides as terminating molecules were also attempted. The primary formation of cyclic products of monomer intramolecular glycosylation was observed in almost all the reactions. Only the experiments with the monomer based on the disaccharide bromide under the conditions of the Helferich reaction led to reduced yields (30%) of the cyclic products. However, even in this case, the desired terminated oligosaccharides were generated in approximately 10% yield and mainly were the products of single glycosylation of the terminator by the monomer. These experiments allow the conclusion that, under the examined conditions, the reaction of terminated oligomerization could not result in the synthesis of oligoglucosamines with a high molecular mass.

Synthesis and serological characterization of L-glycero-alpha-D-manno-heptopyranose-containing di- and tri-saccharides of the non-reducing terminus of the Escherichia coli K-12 LPS core oligosaccharide

Synthesis of the title trisaccharide was accomplished by sugar chain extension starting from the non-reducing terminus: coupling of Glcp NAc with LD-Hepp, then adding Glcp-OAll. An alternative route started from the reducing end: coupling of LD-Hepp with Glcp-OAll, then addition of Glcp NAc. In the synthesis of the title disaccharide a modification of the first approach was employed. The allyl glycosides were coupled with cysteamine, activated with thiophosgene and conjugated to bovine serum albumin (BSA). The neoglycoconjugates obtained were used in immunochemical studies of monoclonal and polyclonal antibodies directed against Escherichia coli K-12 lipopolysaccharide.