A novel two-step synthesis of α-linked mannobioses based on an acid-assisted reverse hydrolysis reaction

Like Visiting an Old Friend: Fischer Glycosylation in the Twenty-First Century: Modern Methods and Techniques

Fischer glycosylation is typically the chemical reaction of a monosaccharide and an alcohol in presence of an acidic catalyst to afford glycosides in pyranosidic and furanosidic forms. This reaction is still applied today for the synthesis of specialized glycosides, and optimization and modification of the method have continued since its discovery by Emil Fischer in the 1890s. This review presents advancements in Fischer glycosylation described in literature of the past 15 years and its implementation in modern chemical methods.

A novel strategy for efficient disaccharides synthesis from glucose by β-glucosidase

Oligosaccharides have important therapeutic applications. A useful route for oligosaccharides synthesis is reverse hydrolysis by β-glucosidase. However, the low conversion efficiency of disaccharides from monosaccharides limits its large-scale production because the equilibrium is biased in the direction of hydrolysis. Based on the analysis of the docking results, we hypothesized that the hydropathy index of key amino acid residues in the catalytic site is closely related with disaccharide synthesis and more hydrophilic residues located in the catalytic site would enhance reverse hydrolysis activity. In this study, positive variants TrCel1bI177S, TrCel1bI177S/I174S, and TrCel1bI177S/I174S/W173H, and one negative variant TrCel1bN240I were designed according to the Hydropathy Index For Enzyme Activity (HIFEA) strategy. The reverse hydrolysis with TrCel1bI177S/I174S/W173H was accelerated and then the maximum total production (195.8 mg/mL/mg enzyme) of the synthesized disaccharides was increased by 3.5-fold compared to that of wild type. On the contrary, TrCel1bN240I lost reverse hydrolysis activity. The results demonstrate that the average hydropathy index of the key amino acid residues in the catalytic site of TrCel1b is an important factor for the synthesis of laminaribiose, sophorose, and cellobiose. The HIFEA strategy provides a new perspective for the rational design of β-glucosidases used for the synthesis of oligosaccharides.

Preferential binding of E. coli with type 1 fimbria to D-mannobiose with the Manα1 → 2Man structure

Manα1 → 2Man, Manα1 → 3Man, Manα1 → 4Man, and Manα1 → 6Man were converted to the glycosylamine derivatives. Then, they were mixed with monobenzyl succinic acid to obtain their amide derivatives. After removing the benzyl group by hydrogenation, the succinylamide derivatives were coupled with the hydrazino groups on BlotGlyco™ beads in the presence of water-soluble carbodiimide. d-Mannobiose-linked beads were incubated with fluorescence-labeled Escherichia coli with type 1 fimbria, and the number of the fluorescent dots associated with the beads was counted in order to determine the binding preference among d-mannobiose isomers. The results showed that the bacteria bind strongly to Manα1 → 2Man1 → beads, Manα1 → 3Man1 → beads, Manα1 → 4Man1 → beads, and Manα1 → 6Man1 → beads, in order. In the presence of 0.1 M methyl α-d-mannopyranoside, most of the bacteria failed to bind to these beads. These results indicate that E. coli with type 1 fimbria binds to all types of d-mannobiose isomers but preferentially to Manα1 → 2Man disaccharide.