Extending the Scope of GTFR Glucosylation Reactions with Tosylated Substrates for Rare Sugars Synthesis

Abstract

Functionalized rare sugars were synthesized with 2-, 3-, and 6-tosylated glucose derivatives as acceptor substrates by transglucosylation with sucrose and the glucansucrase GTFR from Streptococcus oralis. The 2- and 3-tosylated glucose derivatives yielded the corresponding 1,6-linked disaccharides (isomaltose analogues), whereas the 6-tosylated glucose derivatives resulted in 1,3-linked disaccharides (nigerose analogue) with high regioselectivity in up to 95 % yield. Docking studies provided insight into the binding mode of the acceptors and suggested two different orientations that were responsible for the change in regioselectivity.

Enzymatic Synthesis of Artificial Polysaccharides

“…Upon sucrose binding in the subsites −1 and +1, the cleavage of the glycosidic linkage results in a covalent β-glucosyl- or α-fructosyl-enzyme intermediate, with the stereogenic center of the monosaccharides inverted with respect to their configuration in the donor. The retaining mechanism further proceeds through a second transition state and the nucleophilic attack of the acceptor substrate onto the covalent glycosyl-enzyme intermediate to yield a glycosylated product. , Sucrases are naturally promiscuous in relation to the type of acceptor molecules that they recognize, permitting the glycosylation of various saccharides and aglycone substrates. − …”