Alf Gunnarsson

N-andO-alkylation of glycoconjugates and polysaccharides by solid base in dimethyl sulphoxide/alkyl lodide

O-Methylation of simple neutral oligosaccharides is readily accomplished in dimethyl sulphoxide containing solid sodium hydroxide and methyl iodide [Cincanu I, Kerek F (1984) Carbohydr Res 131∶209-17]. This procedure has been extended to 2-acetamido-2-deoxy sugars and sialic acid-containing oligosaccharides. CompleteO-andN-methylation was in most cases achieved in 15 min. Esterification of carboxylic groups in uronic acids was fast and resulted in concomitant β-elimination. The method is also suitable for methylation of glycoproteins and glycosphingolipids. Polysaccharides can also be methylated by this technique. Analysis of the products by gas-liquid chromatography and mass spectrometry showed no degradation products.

Synthesis of Galβ1-3GlcNAc and Galβ1-3GlcNAcβ-SEt by an enzymatic method comprising the sequential use of β-galactosidases from bovine testes andEscherichia coli

Galβ1-3GlcNAc (1) and Galβ1-3GlcNAcβ-SEt (2) were synthesized on a 100 mg scale by the transgalactosylation reaction of bovine testes β-galactosidase with lactose as donor andN-acetylglucosamine and GlcNAcβ-SEt as acceptors. In both cases the product mixtures contained unwanted isomers and were treated with β-galactosidase fromEscherichia coli which has a different specificity, under conditions favouring hydrolysis, yielding besides the desired products, monosaccharides and traces of trisaccharides. The products were purified to >95% by gel filtration, with a final yield of 12% of 1 and 17% of 2, based on added acceptor. In a separate experiment Galβ1-6GlcNAcβ-SEt (3) was synthesized by the transglycosylation reaction using β-galactosidase fromEscherichia coli. No other isomers were detected. Compound 3 was purified by HPLC.

Synthesis of mannose oligosaccharides via reversal of the α-mannosidase reaction

SummaryThree naturally occurring isomers of the disaccharideO-α-d-mannosyl-d-mannoside were synthesized by reversing the hydrolytic activity of jack bean α-mannosidase at 75°C in a very high concentration of mannose. Higher oligosaccharides were also obtained at the later stages of the reaction. The maximum total yield of disaccharides was 37% (w/w) based on the total amount of saccharides.

Studies of the reversed α-mannosidase reaction in high concentrations of mannose

Abstract The reversal of the hydrolytic activity of α-mannosidase from jack bean has been studied in high concentrations of mannose. From an initial concentration of 85% mannose (w/w), a maximum yield of 70% (w/w) di- and oligosaccharides was obtained. The products were separated by gel chromatography and high-performance liquid chromatography, and characterized by gas-liquid chromatographymass spectrometry and 1 H-nuclear magnetic resonance spectroscopy. The equilibrium for the formation of di- and oligosaccharides was investigated, and the equilibrium constant for the formation of disaccharides was calculated to be 5.5 ± 0.9. The stability of the enzyme and the rate of formation of disaccharides were studied as functions of temperature, pH, and starting concentration of mannose. It was shown that the enzyme was not inhibited by a total sugar concentration of 83% (w/w), compared with 40%.

The reactivity of uronic and aldonic acid derivatives towards trifluoroacetolysis. A new method for specific elimination of reducing 4-O-substituted hexose residues

Abstract Trifluoroacetolysis of d -glucuronic acid and methyl α- d -glucopyranosiduronic acid resulted in an initial phase of degradation followed by stabilisation of the compounds as their 6,3-lactones. The methyl ester of methyl 4-O-methyl-α- d -glucopyranosiduronic acid was largely stable towards trifluoroacetolysis. Aldonic acids substituted at O-3 or O-6 were stable towards trifluoroacetolysis because of the formation of γ-lactones. Aldonic acids substituted at O-4, and incapable of forming γ-lactones, were converted into the trifluoroacetylated enol of 3-deoxy-2-hexulosonic acid. Treatment of the 3-deoxy-2-hexulosonic acid with mild base eliminated the substituent at O-4.

Degradation of chondroitin 4-sulphate by tri-fluoroacetolysis: isolation of oligosaccharides from the carbohydrate-protein linkage region

Oligosaccharides from the linkage-region tetrasaccharide, beta-D-GlcpA-(1----3)-beta-D-Galp-(1----3)-beta-D-Galp-(1----4)-D- Xylp, of chondroitin 4-sulphate were isolated after trifluoroacetolysis. The oligosaccharides were purified by ion-exchange chromatography and paper chromatography and subjected to sugar and methylation analysis and g.l.c.-m.s. The recovery of linkage-region oligosaccharides was approximately 45% after trifluoroacetolysis, calculated according to the D-xylose present in the chondroitin 4-sulphate preparation. The following structures were identified: beta-D-Galp-(1----4)-D-Xylp, beta-D-Galp-(1----3)-D-Galp, beta-D-Galp-(1----3)-beta-D-Galp-(1----4)-D-Xylp, beta-D-GlcpA-(1----3)-beta-D-Galp-(1----3)-beta-D-Galp-(1----4)-D- Xylp.