The need for stereoselective and high
yielding glycosylation reactions are two of the important problems to be solved
in synthetic carbohydrate chemistry.
With this goal we developed a new
type of donor that is easy to prepare, reactive, high yielding and
stereoselective. This was done by making 3,6-tethered thio glycosyl donors in
the gluco, manno, galacto and 2-azidogluco series by using the di-tert-butylsilyl protection group as tethering
group. The new donors were investigated by NMR and found to be in unusual axial
rich conformations.
The donors were tested in
glycosylation reactions where the stereoselectivity and the reactivity were evaluated.
It was found that some of the donors were very selective in glycosylation
reactions, and some of the donors were found to be highly reactive (i.e. super
armed)1. The reactivity also depended
on the configuration of the leaving group.
The thio glycosides were converted to
glycosyl fluorides and used as donors under the Yamada-conditions2 which in some cases changed the selectivity dramatically.
1 Pedersen, C.M., Nordstrøm, L.U., Bols, M., JACS, 2007, 129 (29),
9222-9235, Heuckendorff, M., Pedersen, C.M., Bols,
M., Chem. Eur. J. 2010, (16), 13982 – 13994, Heuckendorff,
M., Pedersen, C.M., Bols, M., J. Org. Chem. 2012, (77), 5559−5568
2 Okada,
Y., Asakura, N., Bando, M., Ashikaga, Y., Yamada, H., JACS, 2012, 134 (16), 6940-6943
