Strategy polysaccharide synthesis

The wide availability of various polysaccharides provides an important source of some of the monosaccharides. Such monosaccharides are now used in organic reactions as low-cost starting materials in the synthesis of a range of simpler optically pure compounds (e.g. Expt 5.77). These synthetic strategies have been made possible from earlier work on the development of numerous selective protection methods, on the application of new selective reagents for functional group modification within the monosaccharide molecule, and on the realisation of the role of conformation in the interpretation of a reaction course. The preparative examples in this section are illustrative of these developments. 

The Ley group s synthesis of a Tryp. brucei GPI showcased a great improvement, as far as efficiency is concerned, over the first report by Ogawa. These improvements came in the form of a more convergent strategy, a more rapid assembly of key polysaccharide building blocks, and also a much shorter synthesis of the inositol building block 28. 

The selective preparation of 1,2-czs-linkages in the D-manno and L-rhamno series is still one of the major challenges in oligosaccharide synthesis. Several new and promising approaches deal with this problem [59]. Since a number of pyru-vated oligo- and polysaccharides also contain o-mannosyl and j -L-rhamnosyl residues (Table 1), eCBcient strategies for their preparation are also needed here. 

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