- The Glycosylation Mechanisms of 6,3-Uronic Acid Lactones
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Uronic acids are important constituents of polysaccharides found on the cell membranes of different organisms. To prepare uronic-acid-containing oligosaccharides, uronic acid 6,3-lactones can be employed as they display a fixed conformation and a unique reactivity and stereoselectivity. Herein, we report a highly β-selective and efficient mannosyl donor based on C-4 acetyl mannuronic acid 6,3-lactone donors. The mechanism of glycosylation is established using a combination of techniques, including infrared ion spectroscopy combined with quantum-chemical calculations and variable-temperature nuclear magnetic resonance (VT NMR) spectroscopy. The role of these intermediates in glycosylation is assayed by varying the activation protocol and acceptor nucleophilicity. The observed trends are analogous to the well-studied 4,6-benzylidene glycosides and may be used to guide the development of next-generation stereoselective glycosyl donors.
- Elferink, Hidde,Mensink, Rens A.,Castelijns, Wilke W. A.,Jansen, Oscar,Bruekers, Jeroen P. J.,Martens, Jonathan,Oomens, Jos,Rijs, Anouk M.,Boltje, Thomas J.
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- Construction of N-glycan microarrays by using modular synthesis and on-chip nanoscale enzymatic glycosylation
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An effective chemoenzymatic strategy is reported that has allowed the construction, for the first time, of a focused microarray of synthetic N-glycans. Based on modular approaches, a variety of N-glycan core structures have been chemically synthesized and covalently immobilized on a glass surface. The printed structures were then enzymatically diversified by the action of three different glycosyltransferases in nanodroplets placed on top of individual spots of the microarray by a printing robot. Conversion was followed by lectin binding specific for the terminal sugars. This enzymatic extension of surface-bound ligands in nanodroplets reduces the amount of precious glycosyltransferases needed by seven orders of magnitude relative to reactions carried out in the solution phase. Moreover, only those ligands that have been shown to be substrates to a specific glycosyltransferase can be individually chosen for elongation on the array. The methodology described here, combining focused modular synthesis and nanoscale on-chip enzymatic elongation, could open the way for the much needed rapid construction of large synthetic glycan arrays. Go nano! Arrays of immobilised carbohydrates can be enzymatically processed with the help of glycosyl transferases in nanodroplets placed on top of individual spots. This methodology opens the way for the stereospecific on-chip construction of glycan arrays with very high ligand densities by using immobilised synthetic glycan scaffolds and minute amounts of recombinant glycosyltransferases (see figure).
- Serna, Sonia,Etxebarria, Juan,Ruiz, Nerea,Martin-Lomas, Manuel,Reichardt, Niels-Christian
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supporting information; experimental part
p. 13163 - 13175
(2011/02/24)
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