text: Glycosynthase have been useful for the preparation of oligosaccharides; however, their use suffers from certain limitations.  First, glycosynthase can only be used to synthesize glycosidic linkages for which there is a known glycosidase.  That glycosidase must also be first converted into a glycosynthase, which is not always possible.  Second, the product of the glycosynthase reaction is often a better substrate for the glycosynthase then the starting material, resulting in the formation of multiple products of varying lengths.  Finally, glycosynthase are specific for the donor sugar but often have loose specificity for the acceptor sugar.  This can result in different regioselectivity depending on the acceptor resulting in products with different glycosidic linkages.  One example is the Agrobacterium sp. β-glucosynthase, which forms a  β-1,4-glycoside with glucose as the acceptor, but forms a β-1,3-glycoside with xylose as the acceptor.