Formation of a Glycoside

The base lability of succinoyl diester hnker severely limits the selection of protecting groups available for an oligosaccharide synthesis, so a more versatile tether was required. Diether bonds of benzylphenol or dibenzyl of 1,4-di(hydroxymethyl)-benzene satisfy this requirement because they are stable to both bases and to acids. A sufficient acid stability is important since the formation of a glycosidic bond is an acid-catalyzed reaction, not surprisingly, as it is an acetal functionality. For instance, DOX,34 the dibenzyl hnker a,a -DiOxyXylyl diether, -0CH2C6H4CH20-, is not limited by restriction of the succinoyl hnker (1) when bound via a hydroxyl or as an... 

One of the most interesting ribozymes isolated by in vitro selection techniques is a novel catalytic RNA that promoted the formation of a glycosidic bond... 

Write all of the steps in the mechanism for the formation of a glycoside from a given sugar and alcohol. 

The stereoselective formation of a glycosidic bond is the key feature of oligosaccharide synthesis. Despite the many powerful glycosylation methods that have been developed, there are still a few glycosidic linkages that are difficult to synthesise. For example, the / -mannosidic bond presents a synthetic challenge because the anomeric effect favours the formation of... 

Hansson and Rosengren135 reported the first application of the ion-pair alkylation procedure136 to the formation of a glycosidic bond in the preparation of 45. Alkylation of tetrabutylammonium 2-(benzyl-oxy)-4-formylphenolate (prepared in situ from the aldehyde plus tetrabutylammonium hydrogensulfate, followed by extraction of the ion pair with dichloromethane) with the bromide 1 gave a mixture of 45 and methyl 3,4,5-tri-0-acetyl-2,6-anhydro-D-Zj/xo-hex-5-enonate (6) in 28 and 37% yield, respectively the former was obtained pure by chro-... 

Veeneman, G H, van Boom, J H, An efficient thioglycoside-mediated formation of a-glycosidic linkages promoted by iodonium dicollidine perchlorate. Tetrahedron Lett., 31, 275 - 278, 1990. 

It is not possible to define in detail the structure of the intermediate ion-pairs or transition states involved in the formation of a-glycosides. Nevertheless a solvent of good donor properties and low dielectric constant is clearly the sine... 

D-Xylose is unusual as a structural component in mammalian cells. It is only present as the linker between protein and carbohydrate in proteoglycans, a class of extracellular macromolecules composed of glycosaminoglycan (GAG) chains attached to a core protein. Biosynthesis of GAG chains starts with the formation of a glycosidic bond between a serine residue of the protein and the unique o-xylose of the GAG chain. Then a specific linker tetrasaccharide is synthesized and is used as the acceptor for the elongation of GAG chains (Fig. 8). 

---