Oligosaccharide syntheses blocks

The synthesis is an excellent example of the use of thioglycosides as glycosyl donors in the block synthesis of complex oligosaccharides as well as the use of partial glycosylation of diols to achieve short paths to the target. 

In conclusion, the phenyl selenoglycosides are versatile building blocks for oligosaccharide synthesis. Through judicious choice of protecting groups, and particularly promoters, they can be exploited as either donors or acceptors in glycosylation... 

The sulfated oligosaccharides discussed above were highly, but not completely, sulfated so that mixtures of compounds with a slightly different sulfation pattern resulted. An attempt to understand which sulfation site was important for the biological activity of tetrasaccharide 15 was made by the synthesis of mono-and oligodeoxygenated analogues of 15. These tetrasaccharides were prepared in a block synthesis approach comparable to the synthesis of 15, and the deoxy functions were essentially introduced on the di- or tetrasaccharide level. A representative synthetic example is depicted in Scheme 4 [44]. 

B. A. Dmitriev, A. V. Nikolaev, A. S. Shashkov, and N. K. Kochetkov, Block-synthesis of higher oligosaccharides Synthesis of hexa- and nona-saccharide fragments of the O-antigenic polysaccharide of Salmonella newington, Carbohydr. Res., 100 (1982) 195-206. 

Sect. 2 below summarizes some of the important structures containing pyruvic acid acetals. The structural diversity, methods for structure elucidation, biosynthesis and biological function of these oligo- and polysaccharides will be briefly discussed. Sect. 3 gives an overview of the synthetic methods for the stereoselective preparation of pyruvated building blocks for oligosaccharide synthesis. Here, special attention is paid to pyruvated glycosyl donors, and their application to the synthesis of selected structures is presented in Sect. 4. 

The most convenient procedure for the efficient preparation of pyruvated building blocks for oligosaccharide synthesis is the direct acid-catalysed acetalation of a glycoside with methyl pyruvate. As mentioned above, this procedure affords carefully optimized conditions. Thus, early attempts in this direction showed that acceptable yields of pyruvated glycosides can only be obtained if small amounts are prepared [16,28b, 37]. The conditions are not suitable for the pre-... 

Bogusiak, J, Szeja, W, Block synthesis of oligosaccharides. Part 1 preparation of furanosyl-1-thiopyranosides, Tetrahedron Lett., 42, 2221-2223, 2001. 

For the synthesis of higher oligosaccharides, two major strategies can be considered. These include the stepwise synthesis and the block synthesis. These two strategies are illustrated for the synthesis of a linear ABCD tetrasaccharide in Scheme 5.2 and Scheme 5.3. 

In the block synthesis, the target oligosaccharide is assembled from a few smaller ohgosaccharides. As shown in Scheme 5.3, for the synthesis of an ABCD oligosaccharide the AB (17) and CD (8) disaccharide blocks are synthesized in parallel and coupled after a single deprotection step (8 9) to afford the protected tetrasaccharide (14). 

The synthesis of pneumococcal oligosaccharides serotype 14 (consisting of multiple repeat units) utilizing a block synthesis strategy was reported by Oscarson.72 In accordance with the strategy developed, galactosyl bromide donor 57 was... 

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