Functionalized C-Glycoside Ketohydrazones: Carbohydrate Derivatives that Retain the Ring Integrity of the Terminal Reducing Sugar

Glycosylation often mediates important biological processes through the interaction of carbohydrates with complementary proteins. Most chemical tools for the functional analysis of glycans are highly dependent upon various linkage chemistries that involve the reducing terminus of carbohydrates. However, because of ring opening, the structural integrity of the reducing sugar ring (pyranose or furanose) is lost during these techniques, resulting in derivatized carboydrates that markedly differ from the parent molecule. This paper describes a new aqueous-based, one-pot strategy that involves first converting the sugar to a C-glycoside ketone, followed by conversion to ketohydrazones or oximes. Hence, the C-glycoside ketones are tagged with fluorescence, colored, cationic or biotin-labeled groups or immobilized onto hydrazine-functionalized beads. No activating or protecting groups are required, and the chemistry is mild enough for a wide range of carbohydrates. We demonstrate the versatility of the approach to diverse glycans, including bead immobilization and lectin analysis of acarbose, an antidiabetic drug, to dabsyl-tagged enzyme substrates to screen cellulases, and for the analysis of plant cell wall hemicellulosics.