The synthesis of compatible solute analogues-solvent effects on selective glycosylation

Ethyl 6-O-acetyl-2,3,4-tribenzyl-1-d-thioglucoside and ethyl 6-O-acetyl-2,3,4-tribenzyl-1-d-thiogalactoside, as a mixture of anomers, were employed in the study of the influence of solvent in the stereoselectivity of the glycosylation reaction with small and reactive acceptors. High α-selectivities were obtained in the glycosylation reactions using NIS/TfOH as activator and ethyl ether as the solvent at -60°C. Other solvent mixtures such as dichloromethane, THF, THF/ethyl ether and toluene/dioxane were not nearly as selective. The corresponding thiogalactoside underwent similar glycosylations with the same solvents but with low anomer selectivity. These glycosides are key intermediates for the synthesis of new analogues of compatible solutes.