Heptasaccharide phytoalexin elicitor synthesis

Nicolau, K. C., Winssinger, N., Pastor, J., and DeRoose, F. (1997) A general and highly efficient solid phase synthesis of oligosaccharides. Total synthesis of a heptasaccharide phytoalexin elicitor (HPE)../. Am. Chem. Soc. 119,449—450. 

The addition of a second, reducing end acceptor and a thiophilic promoter (NIS) resulted in trisaccharide formation. Yields as high as 84% for the overall process were reahzed, showcasing the efficiency of this strategy as well as the promoter compatibility, which can be a problem (Fig. 3). The method has been extended to branched structures as well (34). Takahashi has advanced the orthogonal OPG strategy in an impressive synthesis of the heptasaccharide phytoalexin elicitor (HPE) in 24% overall yield (35). 

The second example is a solid-phase synthesis of a heptasaccharide phytoalexin elicitor. Here, attachment of the polymer was to the reducing end of the oligosaccharide. The structure was chosen as an example for the development of... 

Scheme 4.21 Mukaiyama s one-pot synthesis of phytoalexin-elicitor active heptasaccharide.

P. FOgedi, W. Birberg, P. J. Garegg, and A. Pilotti, Synthesis of a branched heptasaccharide having phytoalexin-elicitor activity, Carbokydr. Res 164 797 (1987). 

The glucoheptaose 13, which has phytoalexin elicitor activity, has been prepared using a polymer- supported solution synthesis. Compound 14 with A/-phthaloylation was made as a fully substituted glycosyl azide in work associated with tumour-related A -bonded glycans, and related work on glycoprotein led to the preparation of the xylose-containing heptasaccharide 15. ... 

This octopus concept is impressive in that a large number of glycosylated branches are created in one reaction but this strategy was found difficult to continue at the next level due to steric hindrance and moderate yields in per-allylation and per-hydroboration. As a consequence a convergent approach have been preferred in larger constructions. Colonna et al. have described the preparation of a dendrimer with three heptasaccharide elements which was inspired by Polotti s work on the synthesis of the phytoalexin elicitor analogues. ... 

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