Glycopeptide Synthesis in Solution and on the Solid Phase

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]. 

Carbohydrates and polysaccharides, on the one hand, and peptides and proteins, on the other, have been considered as separate classes of natural products for a long time. Fundamental chemical methodology for the synthesis of both saccharides and peptides was developed by Emil Fischer et al. at the beginning of the 20th century. 1,2 However, the harsh conditions employed in early solution and solid-phase peptide synthesis hindered the combination of peptide and carbohydrate chemistry, i.e. glycopeptide synthesis. Considerable efforts were made to combine the two branches of natural product chemistry, and the state of the art within glycopeptide synthesis has improved dramatically during the last decades, as described in a number of reviews. 3 23,512"514 ... 

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