Chemoselective glycosylations .2. Differences in size of anomeric leaving groups can be exploited in chemoselective glycosylations

We have developed a novel chemoselective glycosylation strategy. This glycosylation strategy is based on the fact that the glycosyl reactivity of an anomeric thiol group can be controlled by the bulkiness of this group whereby we have produced a new range of differentially reactive coupling substrates. It was also shown that the anomeric configuration of the thioglycosides affects the reactivity of the substrates. The new approach will enable complex oligosaccharides of biological importance to be prepared in a highly convergent manner. The versatility of this approach is demonstrated by the synthesis of pentasaccharide 34 from the building blocks 7, 9, 10, 12, and 14 without a single protecting group manipulation.