Phosphates disaccharides

The key step in the preparation of the inhibitor is shown in Scheme 1.4.10 and involves the elaboration of the glucose derivative, shown, to the olefin on reaction with methylenetriphenylphosphorane. Once the olefin was isolated, the C-glycoside was obtained via mercury mediated cyclization followed by oxidation of the mercury with iodine. Further elaboration of the resulting iodide gave the desired C-phosphate disaccharide shown. 

Trehalose 6-phosphate has been prepared in 28% yield through unimolar phosphorylation of the disaccharide with diphenyl phos-... 

Baddiley and coworkers42 have studied the structure of S13, which is composed of D-galactose, D-glucose, 2-acetamido-2-deoxy-D-glucose, and ribitol residues, and phosphate groups in the molar proportions 2 1 1 1 1. O-Acetyl groups are also present. A neutral pentasaccharide was obtained by hydrolysis with alkali, followed by enzymic dephosphorylation. On mild, acid hydrolysis, this yielded two main products, a trisaccharide (19) and a disaccharide (20), the structures of which were determined by conventional methods. 

D-glucose-l-phosphate and D-fructose, Hassid, Doudoroff and Barker18 succeeded in crystallizing a non-reducing disaccharide which was indistinguishable from natural sucrose. It was thus that the first laboratory synthesis of sucrose was achieved. 

The fact that this disaccharide, like sucrose, is formed as a result of de-phosphorolytic condensation involving a-D-glucose-l-phosphate supports the view that D-glucose also exists in this disaccharide as the a-form. 

The structural components encountered in E. coli are also present in lipid A of other bacterial sources. Thus, a survey of the structures analyzed shows that lipid A, in general, contain two g/wcoconfigured and pyranosidic D-hexosamine residues (2-amino-2-deoxy-D-glucose, GlcpN, or 2,3-diamino-2,3-dideoxy-D-glucose, GlcpN3N, also termed DAG (49,50)], which are present as a ) -(l — 6)-linked disaccharide (monosaccharide backbones have also been identified, but the respective lipid A lack endotoxic activity). The disaccharide is phosphorylated by one or, in most cases, two phosphate... 

As these results and Fig. 2 show, three structural components may be defined in lipid A (/) the lipid A backbone consisting of a pyranosidic HexN disaccharide and phosphate groups, (ii) substituents of the backbone phosphate residues (polar head groups), and (iii) fatty acids. Therefore, lipid A of different bacteria may be classified according to the nature of the backbone constituents (GlcpN or GlcpN3N), the type and nature of the polar head groups, and features of the acylation pattern. In a few instances, other backbone substituents have been encountered. These will be described later in conjunction with individual lipid A forms. 

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