Increased understanding of the important roles that oligosaccharides and glycoconjugates play in biological processes has led to a demand for significant amounts of these materials for biological, medicinal, and pharmacological studies. Therefore, tremendous effort has been made to develop new procedures for the synthesis of glycosides, whereby the main focus is often the formation of the glycosidic bonds. Accordingly, quite a few review articles have been published over the past few years on glycoside synthesis; however, most are confined to either a specific type of glycoside or a specific strategy for glycoside synthesis. In this Review, new principles for the formation of glycoside bonds are discussed. Developments, mainly in the last ten years, that have led to significant advances in oligosaccharide and glycoconjugate synthesis have been compiled and are evaluated.

A practical approach for the stereoselective introduction of beta-arabinofuranosides has been developed on the basis of locking an arabinosyl donor in a conformation in which nucleophilic attack from the beta face is favored. The new glycosyl donor was designed by analyzing optimized geometries of low-energy conformers of the arabinofuranosyl oxacarbenium ion. The Newman projection of the E(3) conformer indicated that nucleophilic attack from the alpha face is disfavored because an eclipsed H-2 will be encountered. On the other hand, an approach from the beta face was expected to be more favorable, because it will experience only staggered substituents. The arabinofuranosyl oxacarbenium ion could be locked in the E(3) conformation by employing a 3,5-O-di-tert-butylsilane protecting group, which places C-5 and O-3 in a pseudoequatorial orientation, resulting in a perfect chair conformation of the protecting group. The new glycosyl donor gave excellent beta selectivities in a range of glycosylations with glycosyl acceptors having primary and secondary alcohols. The attractiveness of the new methodology was demonstrated by the chemical synthesis of a fragment of arabinogalactan, which is an important constituent of the primary plant cell wall.

The synthesis, characterization, and biological evaluation of novel Ru(II)-and Au(I)-N-heterocyclic carbenes is reported. The NHC-ruthenium(II) complexes (1−6) were synthesized by reacting the appropriately substituted imidazolium bromides with Ag 2 O, forming the NHC-silver bromide in situ followed by transmetalation with dimeric p-cymene ruthenium(II) dichloride. In an analogous manner the NHCgold(I) chloride complexes (NHC-Au(I)Cl) 7−9 were synthesized, utilizing dimethylsulfido gold(I) chloride as the transmetalating agent. The ligand exchange on the NHCgold(I) chlorides was achieved by either reacting the complexes with silver acetate to yield the NHC-gold(I) acetates (NHC-Au(I)OAc) 10−12 or reacting the NHC-gold(I) chlorides under basic conditions with 2′,3′,4′,6′-tetra-O-acetyl-1-thio-β-D-glucopyranose (SR) to give the NHC-gold(I)-(2′,3′,4′,6′-tetra-O-acetyl-β-D-glucopyranosyl-1-thiolate) complexes (NHC-Au(I)SR) 13−15. The Ru(II)-NHC complex 1 and the Au(I)-NHC complex 9 were characterized by single-crystal X-ray diffraction. Also the IC 50 values of these 15 complexes were determined by an MTT-based assay against the human cancer cell lines Caki-1 (renal) and MCF-7 (breast). The Ru(II) complexes 1−6 revealed the following IC 50 values against Caki-1 of >500, 94 (±5), 93 (±2), 170 (±20), 39 (±5), and 13 (±2) μM and against

Die wichtige Rolle, die Oligosaccharide und Glycokonjugate in biologischen Systemen spielen, erfordert immer neue und vor allem größere Mengen dieser Moleküle. Wegen ihrer Heterogenität in natürlichen Vorkommen wurden und werden große Anstrengungen unternommen, um die entscheidende glycosidische Bindung sowohl zwischen einzelnen Kohlenhydratresten als auch zu Aglyconen stereoselektiv und in hoher Ausbeute zu erzeugen. Es existieren nun verschiedene Methoden, die effiziente Synthesen von strukturell definierten komplexen Oligosacchariden und Glycokonjugaten ermöglichen. Das zunehmende Wissen um die bedeutende Rolle, die Oligosaccharide und Glycokonjugate in biologischen Prozessen spielen, hat rasch das Interesse an solchen Verbindungen für biologische, medizinische und pharmakologische Studien geweckt. Deshalb wurden und werden große Anstrengungen unternommen, um neue Methoden für die Synthese von Glycosiden zu entwickeln, wobei das Hauptaugenmerk auf die Bildung der glycosidischen Bindung gerichtet ist. Etliche Übersichtsartikel wurden in den letzten Jahren zur Glycosidsynthese verfasst, die meisten waren jedoch auf einen bestimmten Typ von Glycosiden oder eine bestimmte Methode zur Glycosidsynthese ausgerichtet. In diesem Aufsatz werden neue Prinzipien für die Bildung von glycosidischen Bindungen diskutiert, indem vor allem Arbeiten aus den letzten zehn Jahren berücksichtigt werden, die zu erheblichen Fortschritten in der Oligosaccharid‐ und Glycokonjugatsynthese geführt haben.

Noncaloric artificial sweeteners (NAS) are extensively introduced into commonly consumed drinks and foods worldwide. However, data on the health effects of NAS consumption remain elusive. Saccharin and sucralose have been shown to pass through the human gastrointestinal tract without undergoing absorption and metabolism and directly encounter the gut microbiota community. Here, we aimed to identify a novel mechanism linking intestinal Akkermansia muciniphila and the aryl hydrocarbon receptor (AHR) to saccharin/sucralose-induced nonalcoholic fatty liver disease (NAFLD) in mice. Saccharin/sucralose consumption altered the gut microbial community structure, with significant depletion of A. muciniphila abundance in the cecal contents of mice, resulting in disruption of intestinal permeability and a high level of serum lipopolysaccharide, which likely contributed to systemic inflammation and caused NAFLD in mice. Saccharin/sucralose also markedly decreased microbiota-derived AHR ligands and colonic AHR expression, which are closely associated with many metabolic syndromes. Metformin or fructo-oligosaccharide supplementation significantly restored A. muciniphila and AHR ligands in sucralose-consuming mice, consequently ameliorating NAFLD. IMPORTANCE Our findings indicate that the gut-liver signaling axis contributes to saccharin/sucralose consumption-induced NAFLD. Supplementation with metformin or fructo-oligosaccharide is a potential therapeutic strategy for NAFLD treatment. In addition, we also developed a new nutritional strategy by using a natural sweetener (neohesperidin dihydrochalcone [NHDC]) as a substitute for NAS and free sugars.

In naturally occurring glycopeptides and glycoproteins the glycan residues generally possess N- and O-linkages to the peptide backbone. Here we report the synthesis of the corresponding S-linked glycopeptides by a convergent strategy to provide compounds which should be quite stable to glycosidases. To this end, peptides that contain beta-bromoalanine and gamma-bromohomoalanine were generated either directly by bromination of serine and homoserine residues, respectively, or by standard ligation of the corresponding amino acids. 1-Thiosugars of O-acetyl protected GalNAc, GlcNAc, and lactose were prepared by known procedures. Reaction of the thiosugars with these peptides in an ethyl acetate/water two-phase system, which contained TBAHS and NaHCO(3), or in a one-phase system that consists of DMF/water and which contains NaHCO(3), led to the desired S-linked glycopeptides cleanly and in almost quantitative yield. This reaction also worked well for O-unprotected 1-thiosugars.

Activation of CD1d-restricted invariant NKT (iNKT) cells with the glycolipid α-galactosylceramide (α-GalCer) confers protection against disease in murine models, however, clinical trials in humans have had limited impact. We synthesized a novel thioglycoside analogue of α-GalCer, denoted α-S-GalCer, and tested its efficacy for stimulating human iNKT cells in vitro. α-S-GalCer stimulated cytokine release by iNKT cells in a CD1d-dependent manner and primed CD1d(+) target cells for lysis. α-S-GalCer-stimulated iNKT cells induced maturation of monocyte-derived dendritic cells into antigen-presenting cells that released IL-12 and small amounts of IL-10. The nature and potency of α-S-GalCer and α-GalCer in human iNKT cell activation were similar. However, in contrast to α-GalCer, α-S-GalCer did not activate murine iNKT cells in vivo. Because of its enhanced stability in biological systems, α-S-GalCer may be superior to α-GalCer as a parent compound for developing adjuvant therapies for humans.

The first total synthesis of a thioglycoside analogue of KRN7000, a potential immunostimulant, is described. Two key intermediates are alpha-galactosyl thiol 4 and phytosphingosine derivative 5, which were both prepared from D-galactose.