Abstract
A chemoenzymatic glycosylation remodeling method for the synthesis of selectively fluorinated glycoproteins is described. The method consists of chemical synthesis of a fluoroglycan oxazoline and its use as donor substrate for endoglycosidase (ENGase)-catalyzed transglycosylation to a GlcNAc-protein to form a homogeneous fluoroglycoprotein. The approach was exemplified by the synthesis of fluorinated glycoforms of ribonuclease B (RNase B). An interesting finding was that fluorination at the C-6 of the 6-branched mannose moiety in the Man3GlcNAc core resulted in significantly enhanced reactivity of the substrate in enzymatic transglycosylation. A structural analysis suggests that the enhancement in reactivity may come from favorable hydrophobic interactions between the fluorine and a tyrosine residue in the catalytic site of the enzyme (Endo-A). SPR analysis of the binding of the fluorinated glycoproteins with lectin concanavalin A (con A) revealed the importance of the 6-hydroxyl group on the α-1,6-branched mannose moiety in con A recognition. The present study establishes a facile method for preparation of selectively fluorinated glycoproteins that can serve as valuable probes for elucidating specific carbohydrate-protein interactions.