The formation of highly stereoselective 1,2-cis glycosidic bond is still a major concern in glycochemistry. This is especially true for the preparation of heparan sulfate fragments, when 2-azido-2-deoxy-D-glucosyl donors are involved in the chain elongation process.[1] The low temperature activation of thioglycoside developed by the groups of Crich [2] and van der Marel [3] allows generating and characterizing by NMR highly reactive anomeric triflates. The mechanism of their reaction with a glycosyl acceptor has been investigated by the group of Crich [4] and shown to determine the stereoselectivity of the reaction. We have studied by NMR the formation of anomeric triflates form 2-azido-2-deoxy-D-glucosyl thiophenyl donors and studied the impact of additives A on their reaction with glycosyl acceptors. By performing NMR experiences at low temperature, we were able to show that the reaction of the anomeric triflates with different additives A can lead to the apparition of new reactive species that can explain the observed change in the stereoselectivity of the glycosylation reaction.
Ref.:
1. D. Hamza, R. Lucas, T. Feizi, W. Chai, D. Bonnaffé, A. Lubineau. ChemBioChem. 2006, 7 (12), 1856-1858.
2. D. Crich, M. Smith. J. Am. Chem. Soc. 2001, 123, 9015-9020.
3. J. D. D. Codée, R. E. J. N. Litjens, R. den Heeten, H. S. Overkleeft, J. H. van Boom, G. A. van der Marel. Org. Lett. 2003, 5, 1519-1522.
4. M. Huang, G. Garrett, N. Birlirakis, L. Bohé, D. Pratt, D. Crich. Nature Chemistry 2012, 4, 663-667.
