Abstract
Non-natural oligosaccharides can be expected to exhibit new functions and applications in glycoscience. Enzymatic glycosylation is a powerful tool for the preparation of oligosaccharides with well-defined structure. For example, α-(1→4)-glucosidic linkage can be constructed by α-glucan phosphorylase-catalyzed enzymatic glucosylation using α-D-glucose 1-phosphate (Glc-1-P) as a glycosyl donor. Because this enzyme expresses some loose specificity for recognition of substrate structures, the development of the α-glucan phosphorylase-catalyzed glycosylation using analogue substrates of Glc-1-P is the efficient approach to obtain new non-natural oligosaccharides. In this review, on the basis of above viewpoints, the facile synthesis of non-natural oligosaccharides by the α-glucan phosphorylase-catalyzed enzymatic glycosylations using such analogue substrates, i.e., hexose 1-phosphates as glycosyl donors is described. It has been found that α-D-xylose, α-D-mannose, 2-deoxy-α-D-glucopyranose, 3-or 4-deoxy-α-D-glucose, α-(N-formyl)-D-glucosamine, and α-D-glucuronic acid 1-phosphates are recognized by α-glucan phosphorylase as the glycosyl donor to occur the transfer reaction of the corresponding sugar residues to a non-reducing end of maltooligosaccharides (glycosyl acceptors), giving the non-natural oligosaccharides. Consequently, construction of the new oligosaccharide chains containing the different sugar residue at the non-reducing end by the α-glucan phosphorylase catalysis probably leads to development on new applications of non-natural glyco-substrates.
