b-Glycosyl Azides as Substratesfor a-Glycosynthases: Preparationof Efficient a-L-Fucosynthases

Fucose-containingoligosaccharides play a central role in physio-pathological events, and fucosylated oligosaccharides have interesting potential applications in biomedicine. No methods for the large-scale production of oligosaccharides are currently available, but the chemo-enzymatic approach is very romising. Glycosynthases, mutated glycosidases that synthesize oligosaccharides in high yields, have been demonstrated to be an interesting alternative. However, examples of glycosynthases available so far are restricted to a limited number of glycosidases families and to only one retaining a-glycosynthase. We show here that newmutants of two a-L-fucosidases are efficient a-L-fucosynthases. The approach shown utilized b-L-fucopyranosyl azide as donor substrate leading to transglycosylation yields up to 91%. This is the first method exploiting a b-glycosyl azide donor for a-glycosynthases; its applicability to the glycosynthetic methodology in a wider perspective is presented.