Glycosylation stereochemistry

Wilson LJ, Liotta D (1990) A general method for controlling glycosylation stereochemistry in the synthesis of 2 -deoxtribose nucleosides. Tetrahedron Lett 31 1815-1818... 

Kim KS, Suk DH (2011) Effect of electron-withdrawing protecting groups at remote positions of donors on glycosylation stereochemistry. In Topics in current chemistry. Springer,... 

Effect of Electron-Withdrawing Protecting Groups at Remote Positions of Donors on Glycosylation Stereochemistry... 

Effect of Nonparticipating Electron-Withdrawing Groups at the 0-2 Position of Donors on the Glycosylation Stereochemistry... 

A series of 6-deoxy-6-mono-, di-, and tri-fluoromannopyranosyl donors (6-fluor-orhamnopyranosyl donors) were prepared in order to investigate the effect of increasing electron-deficiency at C6 on glycosylation stereochemistry [46]. All three donors were converted cleanly to observable glycosyl triflates and the thermal stability of these latter species increased with increasing fluorine content at the... 

Structural information chemical formula and stereochemistry in the case of a New Chemical Entity (NCE) or amino acid sequence and glycosylation sites in the case of a biotech product... 

A significant role of lithium in controlling stereochemistry in glycosylation reactions has been reported. In the presence of lithium perchlorate, glycosylation with alcohols proceeds with excellent a-selectivity (Scheme 3).15... 

Sn2 reactions of glycosyl iodides have proven especially advantageous in the synthesis of 2-deoxy P-O-aryl-D-glycosides. This is a challenging linkage to make, as there is no neighboring group to participate. Sometimes, stereochemistry is... 

The sulfoxide method was employed in the direct synthesis of a P-l,2-man-nooctaose (Scheme 4.60) [362-364]. The synthesis of a p-mannosyl phosphoiso-prenoid illustrates the possibility of employing even such weak nucleophiles as phosphates (Scheme 4.61) [365]. Both syntheses rely on the presence of 4,6-0-benzylidene acetal, and its effect on the covalent triflate-contact ion-pair equilibrium [366,367], to influence the stereochemistry of the glycosylation process [295,323],... 

As far as the stereochemistry concerns, when the cyclization occurs through a Michael reaction, the thermodynamic product is generally obtained, but some exceptions have been observed such as that of A-acetyl glucosamine protected as 4,6-benzylidene, the reaction of which with [(ethoxycarbonyl)methylene]triphenylphosphorane afforded the ot-C-glycosyl compound stereoselectively.28... 

The stereochemistry of the reaction of glycosyl radicals is strongly influenced by the anomeric effect. Glucopyranosides and manno-pyranosides afford stereo selectively the a-C-glycosyl compounds whereas in furanosidic structures the stereochemistry is not always predictable. 

A double mutant (acid/base and nucleophile) Abg E71A E358G was developed58 which efficiently catalyzes thioglycoside formation from a glycosyl fluoridine donor (69) with inverted anomeric stereochemistry. This represents a significant improvement, as glycosyl fluoride donors are much more accessible (Fig. 29). 

Crich and Sun propose that path b predominates when the glycosyl acceptor is present during activation of the sulfoxide. However, they have evidence to suggest that when the sulfoxide is activated, prior to addition of the acceptor, the glycosyl triflate forms within minutes.17 This has important consequences in terms of the stereochemistry of the glycosidic linkage. 

In general, the most predictable strategy has been a glycosylation-inversion protocol (i-gluco (1,2-trans) glycosylation followed by the inversion of the C2 stereochemistry by oxidation-reduction40-50 or by S -type replacement (Scheme... 

It has been shown that the stereochemistry of the glycosidic bond to which the carbohydrate component is attached at the neamine core is essential for antibacterial activity. The neomycin class aminoglycoside consists of a neamine core and a P-linked carbohydrate component attached at the 0-5 position, while the kanamycin class aminoglycoside consists of a neamine core with a-linked carbohydrate component attached at the 0-6 position. Since neamine is the pivotal component of both neomycin and kanamycin, a readily accessible library of nnnsnal sugars will provide opportunity for the facile construction of both classes of aminoglycosides via glycosylation approach. 

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