P-Glycosides

Lactam (Section 20 15) A cyclic amide Lactone (Section 19 15) A cyclic ester Lactose (Section 25 14) Milk sugar a disacchande formed by a p glycosidic linkage between C 4 of glucose and C 1 of galactose... 

Manufacture. The hydrolysis of the naturally occurring P-glycoside (saUcin) (8) with hydrochloric or sulfuric acid affords saligenin (9) and glucose (10) (eq. 11). 

Suciose [57-50-1] (P-D-fructofuianosyl-a-D-glucopyianoside), 0 2 22, fomiula weight 342.3, is a disaccharide composed of glucose and fmctose residues joined by an a,P-glycosidic bond (Fig. 1). 

Maltose, obtained by the hydrolysis of starch, and cellobiose, by the hydrolysis of cellulose, are isomeric disaccharides. In both maltose and cellobiose two D-glucopyra-nose units are joined by a glycosidic bond between C-1 of one unit and C-4 of the other. The two are diastereomers, differing only in the stereochemistry at the anomeric car bon of the glycoside bond maltose is an a-glycoside, cellobiose is a p-glycoside. 

Lactose is a disaccharide constituting 2-6% of milk and is known as milk sugar. It differs from maltose and cellobiose in that only one of its monosaccharide units is D-glucose. The other monosaccharide unit, the one that contributes its anomeric carbon to the glycoside bond, is D-galactose. Like cellobiose, lactose is a p-glycoside. 

Most nucleosides contain D-ribose or 2-deoxy-D-ribose linked to N-1 of a pyrimidine or to N-9 of a purine by a P-glycosidic bond whose syn conformers predominate. 

Glycosidation (13,302). Glycosidation of 2-acetamido-3,4,6-triacetyl-2-deoxy-a-D-glucopyranosyl chloride (1) mediated by Sn(OTf)2 provides exclusively P-glycosides. The most satisfactory base is 1,1,3,3-tetramethylurea, and CH2CI2 is the preferred solvent.2... 

Deoxy-P-glycosides are important structural components of many natural products. Recently, 2-deoxy-2-iodoglycosyl trichloroacetimidates [469] have proved to be... 

Acetonitrile is another participating solvent, which in many cases leads to the formation of an equatorially linked glycoside [125-131], It has been proposed that these reactions proceed via an a-nitrilium ion intermediate. It is not well understood why the nitrilium ion adopts an axial orientation however, spectroscopic studies support the proposed anomeric configuration [130,131], It is known that nucleophilic substitution of the a-nitrilium ion by an alcohol leads to P-glycosidic bonds and the best P-selectivities are obtained when reactive alcohols at low reaction temperatures are employed. Unfortunately, mannosides give poor anomeric selec-tivities under these conditions. 

Scheme 5.47 Synthesis of 2-deoxy-a- and P-glycosides using Re(V)-oxo complex.

Scheme 5.52 Preparation of 2-deoxy-2-iodo-(i-glycosy acetates and their use in formation of 2-deoxy-p-glycosides.

General Method for the Preparation of 2-Deoxy-2-lodoglycosylbenzenesulfo-namides from Glycals and Its Use as Glycosyl Donors in the Synthesis of 2-Benzene-sulfonamido-2-Deoxy-P-Glycosides... 

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