Ketoside linkages

Recent evidence (cf. the chapter by Rietschel in this volume) indicates that, in LPS from Proteus mira-b i 1 i s, KDO may be linked to 0-6 of the lipid A-back-bone (the glucosaminyl disaccharide). Conceivably, if the involvement of a primary oxygen function in this ketosidic linkage were substantiated, this would considerably facilitate attempts at the synthesis of oligosaccharides containing the lipid A-KD0 linkage. 

The chemistry of sialic acid was pioneered in the late 1960s and focussed on the preferential formation of the a-ketosidic linkage. This is a particularly difficult chemical problem since the anomeric centre sterically and electronically disfavours formation of the oxocarbenium ion intermediate in the course of glycosidation. 

In this chapter, the chemistry of sialic acid is briefly reviewed and some advantages and problems of strategies described for the construction of the a-ketosidic linkage of sialic acid and complicated sialosides are presented. Experimental details are also provided to allow practical preparation of the chosen targets. 

Lipid A. The ketosidic linkage between the terminal core sugar 3-deoxy-D-mfl/mo-octulosonic acid (KDO) and lipid A is acid labile. Hence the hydrophobic lipid A region can be easily separated from isolated LPS by mild acid hydrolysis, followed by chloroform extraction. The structural basis of the LPS extracted from enteric bacteria is a glucosamine disacch-... 

In ganglioside B4(=Bi=GGNTii=GDia) additional N-acetyl-neuraminic acid molecule is linked by a ketosidic linkage to the C 3 of the terminal galactose of ganglioside Bg ... 

Polysialic acid can be composed of 5-V-acetylneuraminic acid (Neu5Ac), 5-V-glycolylneuraminic acid (Neu5Gc), or deaminated neuraminic acid (KDN) residues, which are usually joined by a2,8, a2,9, or alternating a2,8/a2,9 ketosidic linkages [47-53]. 

Each monomer has a functional site on the upper surface of the head domain (Figure 2). The enzyme catalyzes the hydrolysis of the a-ketosidic linkage be-... 

Huang, R. T. C., and Klenk, E., 1972, a-Ketosidic linkage of the neuraminidase-resistant neuraminic acid in brain gangliosides, Hoppe-Seyl. Z. 353 679. 

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