Glycosyltransferases catalyze glycosidic bond formation using sugar donors containing a nucleoside phosphate or a lipid phosphate leaving group. Only two structural folds, GT-A and GT-B, have been identified for the nucleotide sugar-dependent enzymes, but other folds are now appearing for the soluble domains of lipid phosphosugar-dependent glycosyl transferases. Structural and kinetic studies have provided new insights. Inverting glycosyltransferases utilize a direct displacement S(N)2-like mechanism involving an enzymatic base catalyst. Leaving group departure in GT-A fold enzymes is typically facilitated via a coordinated divalent cation, whereas GT-B fold enzymes instead use positively charged side chains and/or hydroxyls and helix dipoles. The mechanism of retaining glycosyltransferases is less clear. The expected two-step double-displacement mechanism is rendered less likely by the lack of conserved architecture in the region where a catalytic nucleophile would be expected. A mechanism involving a short-lived oxocarbenium ion intermediate now seems the most likely, with the leaving phosphate serving as the base.

Glycosyltransferases: structures, functions, and mechanisms.

Synthetic oligosaccharides and glycoconjugates are increasingly used as probes for biological research and as lead compounds for drug and vaccine discovery. These endeavors are, however, complicated by a lack of general methods for the routine preparation of this important class of compounds. Recent development such as one-pot multi-step protecting group manipulations, the use of unified monosaccharide building blocks, the introduction of stereoselective glycosylation protocols, and convergent strategies for oligosaccharide assembly, are beginning to address these problems. Furthermore, oligosaccharide synthesis can be facilitated by chemo-enzymatic methods, which employ a range of glycosyl transferases to modify a synthetic oligosaccharide precursor. Glycosynthases, which are mutant glycosidases, that can readily form glycosidic linkages are addressing a lack of a wide range glycosyltransferases. The power of carbohydrate chemistry is highlighted by an ability to synthesize glycoproteins.

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Opportunities and challenges in synthetic oligosaccharide and glycoconjugate research

Sialic acids are a subset of nonulosonic acids, which are nine-carbon α-keto aldonic acids. Natural existing sialic acid-containing structures are presented in different sialic acid forms, various sialyl linkages, and on diverse underlying glycans. They play important roles in biological, pathological, and immunological processes. Sialobiology has been a challenging and yet attractive research area. Recent advances in chemical and chemoenzymatic synthesis, as well as large-scale E. coli cell-based production, have provided a large library of sialoside standards and derivatives in amounts sufficient for structure−activity relationship studies. Sialoglycan microarrays provide an efficient platform for quick identification of preferred ligands for sialic acid-binding proteins. Future research on sialic acid will continue to be at the interface of chemistry and biology. Research efforts not only will lead to a better understanding of the biological and pathological importance of sialic acids and their diversi...

Advances in the Biology and Chemistry of Sialic Acids

The discovery of previously unknown functions associated with carbohydrates and the study of their structure-function relations are of current interest in carbohydrate chemistry and biology. Progress in this area is, however, hampered by the lack of convenient and effective tools for the synthesis and analysis of oligosaccharides and glycoconjugates. Development of automated synthesis of such materials is necessary to facilitate research in this field. This review describes recent advances in carbohydrate synthesis, with particular focus on developments that have potential application to the automated synthesis of oligosaccharides, glycopeptides, and glycoproteins.

https://science.sciencemag.org/content/sci/291/5512/2344.full.pdf

Toward automated synthesis of oligosaccharides and glycoproteins.

The review compiles artificial cascades involving enzymes with a focus on the last 10 years. A cascade is defined as the combination of at least two reaction steps in a single reaction vessel without isolation of the intermediates, whereby at least one step is catalyzed by an enzyme. Additionally, cascades performed in vivo and in vitro are discussed separately, whereby in vivo cascades are defined here as cascades relying on cofactor recycling by the metabolism or on a metabolite from the living organism. The review introduces a systematic classification of the cascades according to the number of enzymes in the linear sequence and differentiates between cascades involving exclusively enzymes and combinations of enzymes with non-natural catalysts or chemical steps. Since the number of examples involving two enzymes is predominant, the two enzyme cascades are further subdivided according to the number, order, and type of redox steps. Furthermore, this classification differentiates between cascades where al...

Artificial Biocatalytic Linear Cascades for Preparation of Organic Molecules

Sulfuric acid immobilized on silica gel (H2SO4-SiO2) was used as an efficient and convenient promoter for Ferrier-type rearrangement of 3,4,6-tri-O-benzyl-d-glucal in CH2Cl2, which is a difficult donor for this type of reaction. The acceptors include primary alcohols, secondary alcohols, pentanol, halogenated alcohol, sterols, thiol, and 2-naphthol. Thus, 2,3-unsaturated glycosides were obtained rapidly ( 62%) in good α-selectivity (α/β>4.2:1) under mild conditions.

A Facile H2SO4—SiO2‐Catalyzed Ferrier Rearrangement of 3,4,6‐Tri‐O‐benzyl‐D‐glucal

Convenient per-O-Acetylation of Monosaccharides with Vinyl Acetate/Na3PO4—H2O.

The absolute configuration of the title compound, C12H15NO7·0.5H2O, was assigned from the synthesis. There are two rhamnoside mol­ecules and one water mol­ecule in the asymmetric unit, displaying O—H⋯O hydrogen bonding. One of the nitro groups does not conjugate efficiently with the benzene ring.

https://journals.iucr.org/e/issues/2008/04/00/av2007/av2007.pdf

4-Nitro-phenyl α-l-rhamnopyran-oside hemihydrate.

Degradations and Rearrangement Reactions

The invention discloses a preparation method for a magnetic nano nuclear shell catalyst and an application thereof The method comprises the following steps: using polysaccharide extracted from foliumnelumbinis as a carbon source, and loading the polysaccharide on Fe3O4, to obtain a magnetic nano nuclear shell material Fe3O4@C, and immerging the Fe3O4@C in CH2Cl2 solution of FeCl3, washing, drying to obtain a Fe3O4@C@Fe3 catalyst, wherein the catalyst is used for a Ferrier rearrangement reaction of 3,4,6-tri-O-acetyl-D-glucosene and 2-halogeno-(Cl,Br,I)-3,4,6-tri-O-acetyl-glucosene, and catalytic-synthesizing 4,6-diacetyl-2,3-unsaturated glycoside Compared with the prior art, the preparation method has the characteristics of simple process, low production cost, high yield, more moderate reaction conditions, high catalytic efficiency, recycling utilization, cheap price and easy acquisition of raw materials, and extensive application range of a substrate, and is green and environmental, and economic and efficient, and easy to the large-scale industrial production

Jianbo Zhang

Papers

A Facile H2SO4—SiO2‐Catalyzed Ferrier Rearrangement of 3,4,6‐Tri‐O‐benzyl‐D‐glucal

Convenient per-O-Acetylation of Monosaccharides with Vinyl Acetate/Na3PO4—H2O.

4-Nitro-phenyl α-l-rhamnopyran-oside hemihydrate.

Degradations and Rearrangement Reactions

Preparation method for magnetic nano nuclear shell catalyst and application thereof