Polystyrene oligosaccharide synthesis

Scheme 4.8 Use of trichloracetimidate donors of polystyrene supports in solid-phase oligosaccharide synthesis.

Fukase, K, Nakai, Y, Egusa, K, Porco, J A, Kusumoto, S, A novel oxidatively removable linker and its application to a-selective solid-phase oligosaccharide synthesis on a macroporous polystyrene support, Synlett, 1074-1078, 1999. 

Scheme 6.192 shows the o-nitrobenzyl moiety used as a photolabile linker in the solid-phase oligosaccharide synthesis on a polystyrene (PS) support.1208 After the synthesis of the protected oligosaccharide 404, PS attached to the photoremovable group is removed by photolysis and the final product is obtained by hydrogenolysis. Such a strategy could be promising for combinatorial synthesis of oligosaccharide libraries. 

Chiul976 Chiu, S.-H.L. and Anderson, L., Oligosaccharide Synthesis by the Thioglycoside Scheme on Soluble and Insoluble Polystyrene Supports, Carbohydr. Res., 50 (1976) 227-238. 

Danishefsky has developed a solid phase oligosaccharide synthesis strategy based on glycals which are bonded to a polystyrene copolymer via silyl ether bonds and coupled to other glycals. The products were released by use of tetrabutylammonium fluoride. ... 

Polystyrene-based resins have been used successfully for the solid-phase synthesis of glycopeptides and oligosaccharides. Experiments that compare the rates of a reaction on a PS-resin compared to TentaGel have revealed that the rate of reaction completely depends on the nature of the reaction itself [36], Some reactions perform better on hydro-phobic resins, while others are better on hydrophilic resins. Another issue of particular importance for the synthesis of oligosaccharides on solid phase is the influence of the solid support on the stereochemical outcome of the reaction. There are few detailed studies that address this issue however, preliminary results are contradictory, but indicate that as in solution-phase reactions, the anomeric ratio is strongly influenced by the solvent, C-2 group on the donor and temperature [37-39]. In some cases there seems to be an enhancement of anomer selectivity on the solid phase [38]. 

Photolytic cleavage at the anomeric center of glycosides as an analytical or preparative tool does not have a very extensive literature. It has, however, been found useful in the solid-phase synthesis of oligosaccharides. Thus the synthesis by Nicolaou and coworkers of the phytoelicitor heptasaccharide of Phytophthora megasperma (Section V) depends on detachment of the protected heptasaccharide from the support by photolytic cleavage of a 4-nitrophenoxy link to the polystyrene polymer. 

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