Journal of Carbohydrate Chemistry最新文献

An efficient approach for the facile synthesis of a potent vaccine adjuvant RC-529 is described. The synthetic strategy relies on the flexible use of orthogonal protecting groups, which makes it possible to accomplish selective phosphorylation, glycosylation and acylation, respectively. In addition, the use of readily cleaved 2-naphthylmethyl (Nap) ether and allyl esters as permanent protecting groups greatly facilitates the final global deprotection steps to obtain pure RC-529. This work will contribute to the synthesis of lipid A and its derivatives.

An alkali-extracted polysaccharide (HY-B) was isolated and purified from Dioscorea opposita Thunb. (Huai Yam). Its chemical structure was analyzed with FT-IR, GC-MS and 1 D, 2 D-NMR spectrometry. It was proved that HY-B is mainly composed of α-1,4-linked glucose, which is similar to starch, but the starch-iodine color test proved that it was not starch. The chain conformation of HY-B was analyzed by SEC-MALLS-RI and TEM, indicated that HY-B exists in a random coil conformation. Its molecular weight is 18.7 kDa, and the molecular size is about 100 nm. MTT assays indicated that HY-B was nontoxic to RAW 264.7 cells in vitro. The results of anti-inflammatory studies showed that HY-B could inhibit the production of NO and TNF-α in RAW 264.7 macrophage stimulated by lipopolysaccharides (LPSs). This work provided the important information about the anti-inflammatory active component of Huai Yam and its potential applications in the food and health industries.

2-Deoxy-glycosides, in which the C-2 hydroxyl group is replaced with a hydrogen atom, are important motifs in numerous bioactive natural products and pharmaceutical molecules. Herein, an improved dilauroyl peroxide-mediated radical deiodination reaction by using cyclohexane and ethyl acetate as co-solvent is reported. This is an environmentally benign protocol, which operates smoothly under mild conditions and allows efficient preparation of a series of 2-deoxy-glycosides in up to 98% yields.

Sialic acid binding Ig-like lectins (siglecs) are type I membrane proteins characterized by their sequence similarity and ability to bind sialic acid moieties in glycoproteins and glycolipids. Siglecs can regulate the functions of cells in the innate and adaptive immune systems and promote cell–cell interactions through glycan recognition. Siglec-7, a member of the siglec family, is expressed on NK cells and displays unique ligand binding properties different from the other member of the Siglec family. Siglec-7 prefers α(2,8)-disialyl group and branched α(2,6)-sialyl group containing ligands. In this paper, complexes of Siglec-7 in solution with α(2,8)-disialyl group containing ligand GD3, branched α(2,6)-sialyl group containing ligand LSTb and α(2,6)-sialyl group containing ligand LSTc have been modeled based on the crystal structure of Siglec7-DSLc4[α(2,3)/α(2,6)-disialyl lactotetraosyl 2-(trimethylsilyl)ethyl] complex. Structural analysis of these complexes and calculation of theoretical dissociation constant values helped to conclude that GD3 and LSTb can form better complex with Siglec7 than LSTc in solution and all the ligands, DSLc4, GD3, LSTb, and LSTc can form better complexes in solution than in the crystal structure.

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As typical affinities of carbohydrates with their receptors are modest, polymers of carbohydrates (glycopolymers) are exciting tools to probe the multifaceted biological activities of glycans. In this review, the linear glycopolymers and the multivalency effects are first introduced. This is followed by discussions of methods to synthesize these polymers. Subsequently, the interactions of glycopolymers with plant lectins and viral/bacterial carbohydrate binding proteins are discussed. In addition, applications of the glycopolymers in facilitating glycan microarray studies, mimicking cell surface glycans, modulation of the immune system, cryoprotection of protein, and electron-beam lithography are presented to stimulate further development of this fascinating technology.

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Stereoselective glycosidic bond formation (termed “glycosidation”) remains a challenge in carbohydrate chemistry. Despite such difficulty, a variety of innovative strategies have been developed. In particular, additive-modulated stereoselective construction of glycosidic linkages has become an emerging trend. In this review, we summarized the recent progress in this area with respect to common glycosyl donors, including thioglycosides, glycosyl imidates, glycosyl acetates, glycosyl hemiacetals, glycosyl phosphates and glycosyl ortho-alkynylbenzoates. Together with their merits/limitations, these achievements shed light on carbohydrate chemistry and enabled the efficient preparation of complex oligosaccharides and glycoconjugates.

Glycogenolysis and gluconeogenesis are sensitive to nutritional state and their balances are disrupted in the liver by different pathological states. The regulation of the balance between glucose production and synthesis of glycogen continues to be a matter of investigation because of its implications in diseases and its value for therapeutics. We used the gluconeogenic precursor dihydroxyacetone (DHA) to study glycogen synthesis in isolated rat hepatocytes under gluconeogenic conditions. We used a glycogen phosphorylase (GP) inhibitor, 2-deoxy-2-fluoro-α-D-glucopyranosyl fluoride (F₂Glc) to prevented GP from breaking up glycogen into glucose subunits and had a pool of glucose in the medium. Therefore, we evaluated the contribution of DHA as a unique source of carbohydrates on glycogen metabolism. We showed that DHA increased G6P levels that induced both GS activation and its translocation and, thus, an increment of glycogen deposition in a similar way as glucose did.

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An efficient synthetic strategy has been developed for the synthesis of a tetrasaccharide related to the O-specific polysaccharide from Escherichia coli O132 as their 2-aminoethyl glycosides in a very good yield by adopting sequential glycosylation followed by in-situ removal of the p-methoxybenzyl (PMB) group in the same reaction pot. Furthermore, the synthetic route was adapted by carrying out three stereoselective iterative glycosylations followed by in situ removal of the PMB group in one pot. The stereochemical outcomes of all the glycosylation steps were excellent with satisfactory yields.

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