Erzsébet Farkas

Synthesis of the monosaccharide units of the O-specific polysaccharide of Shigella sonnei☆

Abstract The monosaccharide components of the O-specific polysaccharide 1 of the lipopolysaccharide of the enteropathogenic bacterium Shigella sonnei were synthesized as their methyl glycosides 2 and 3 in their natural anomeric form. The key intermediate to the diaminotrideoxygalactose derivative 2 was ethyl 3-O-acetyl-2-deoxy-2-phthalimido-1-thio-β- d -glucopyranoside ( 9 ) that was converted to its ditosylate 10 . Regioselective deoxygenation at C-6 followed by nucleophilic displacement of the secondary tosyloxy group by azide afforded the 4-azido thioglycoside 13 . Methyl trifluoromethanesulfonate-assisted methanolysis of 13 gave the O-glycoside 14 . Replacement of the phthalimido by an acetamido group followed by catalytic reduction of the azido group led to the diamino-trideoxygalactose derivative 2 . The precursor to the l -altruronic acid derivative 3 was methyl α- l -glucopyranoside ( 19 ) that was routinely converted to the benzylidene-protected 2,3-anhydro-allopyranoside 22 . Regioselective opening of the epoxide ring by NaN 3 afforded the 2-azido derivative 23 that was benzylated at HO-3. Hydrolytic removal of the benzylidene group followed by TEMPO oxidation of C-6 and subsequent esterification with MeI gave the key l -azido-altruronic acid intermediate 29 that was transformed to the acetamidoaltruronic acid derivative 3 . High resolution NMR data of the altruronic acid derivatives indicate that the conformation of their pyranose ring is crucially dependent on the substitution pattern: the 2-azido altruronic acid derivatives prefer the 4 C 1 conformation whereas the 2-acetamido congeners exist preferentially in the 1 C 4 conformation.

Synthesis of chromogenic substrates of α-amylases on a cyclodextrin basis

Abstract One-pot acetylation and subsequent partial acetolysis of α-, β- and γ-cyclodextrins resulted in crystalline peracetylated malto-hexaose, -heptaose, and -octaose, respectively. Prolonged acetolysis of β-cyclodextrin gave a mixture of acetylated maltooligosaccharides, from which peracetylated malto-triose, -tetraose, and -pentaose were isolated. The acetylated oligosaccharides were converted into α-acetobromo derivatives, and then transformed into 4-nitrophenyl and 2-chloro-4-nitrophenyl β-glycosides. From the 4-nitrophenyl glycosides 4,6-O-benzylidene derivatives were prepared, which were used together with the free glycosides as substrates of porcine pancreatic α-amylase. One-pot acetylation and subsequent partial acetolysis of cyclodextrins resulted in the peracetylated maltooligomers (dp 3–8), which were transformed into 4-nitrophenyl and 2-chloro-4-nitrophenyl β-glycosides, the 4.6-O-benzylidene derivatives of NP-glycosides were also prepared

Enzymatic synthesis of fucose-containing disaccharides employing the partially purified α-l-fucosidase from Penicilliummulticolor

The alpha-L-Fucp-(1 --> 3)-D-GlcpNAc disaccharide structure is a vital core unit of the oligosaccharide components of glycoconjugates isolated from human milk and blood group substances. Alpha-L-Fucosidase from Penicillium multicolor catalyses the transfer of L-fucose from donor structures such as alpha-L-FucpOpNP and alpha-L-FucpF to various GlcpNAc derivatives and Glcp, forming alpha-(1 --> 3) linkages. The synthesis of several biologically relevant disaccharides including alpha-L-Fucp-(1 --> 3)-alpha-D-GlcpNAcOMe, alpha-L-Fucp-(1 --> 3)-alpha-D-GlcpNAcOAll, alpha-L-Fucp-(1 --> 3)-beta-D-GlcpNAcOAll, alpha-L-Fucp-(1 --> 3)-D-GlcpNAc and alpha-L-Fucp-(1 --> 3)-D-Glcp has been achieved in up to 34% yields by application of this enzyme.

Action pattern of porcine pancreatic alpha-amylase on three different series of β-maltooligosaccharide glycosides

A technique for the investigation of the action pattern of porcine pancreatic amylase (PPA) has been developed by utilising as model substrates 2-chloro-4-nitrophenyl (CNP) and 4-nitrophenyl (NP) beta-glycosides of maltooligosaccharides of dp 4-8 and some NP derivatives modified at the nonreducing end with a 4,6-O-benzylidene (Bnl) group. The action pattern was investigated by the method of product analysis, using an HPLC method. The product pattern and cleavage frequency was very similar in the CNP- and NP-oligomers and showed that the glucopyranose residue could be replaced by the aglycon group. Modification of the nonreducing end of NP glycosides to give a 4,6-O-benzylidene-D-glucopyranosyl group indicated a favourable interaction between the Bnl group and the subsites (-3) and (-5) but an unfavourable one with subsite (-4), which resulted in a clear shift in the product pattern. The results obtained with the digestion of the benzylidene-protected substrates confirm a multiple attack mechanism for PPA.

Galactosylation with β-Galactosidase from bovine testes employing modified acceptor substrates

In this study beta1-3 linked analogues of the T-antigen determinant were synthesized in preparative scale by transgalactosylation using beta-galactosidase from bovine testes to give synthetic antigens. Acceptors with modifications of the sugar residue such as alpha-glycosylated spacers, as well as GlcNAc-alphaOR- and 2dGal-alphaOR-substrates opened further possibilities for galactosylation.

Enzymatic Synthesis of Galactose-Containing Disaccharides Employing β-Galactosidase from Bacillus circulans

Galβ1→4 disaccharide structures are vital core units of the oligosaccharide components of glycoconjugates. β-Galactosidase from Bacillus circulans (E.C.3.2.1.23) catalyses the transfer of galactose from a donor structure such as GalβOpNP to various GlcNAc and galactose derivatives, forming β1→4 linkages. The synthesis of several biologically relevant disaccharides {Galβ1→4GlcNAcαOAll (3), Galβ1→4GlcNAcβOAll (5), Galβ1→4GalαOAll (10), Galβ1→4GalβOAll (12), Galβ1→4GalβSPh (14), Galβ1→4GalβOpNP (16) and the trisaccharide Galβ1→4Galβ1→4GalβOpNP (18)} has been achieved in 30–66 % yield by application of this enzyme.

Synthetic Studies Towards the O-Specific Polysaccharide of Shigella Sonnei

ABSTRACT Synthetic routes are described to zwitter-ionic disaccharides that are diastereoisomerically related to frame-shifted repeating units of the title polysaccharide that contains 2-acetamido-4-amino-2,4,6-trideoxy-D-galactose and 2-acetamido-2-deoxy-L-altruronic acid. The intermediates corresponding to the trideoxygalactose residue feature acylamino functions at C-2 and an azido group at C-4. Best results were obtained with N-phthaloyl- and N-trichloroacetyl-protected derivatives. The intermediates corresponding to the uronic acid residue were either a D-altruronic acid-derived acceptor or a D-altrose-derived donor in which C-6 was oxidized after disaccharide formation.