Sialyl glycosides stereoselectivity

II. Regio- and a-Stereoselective Sialyl Glycoside Syntheses Using Thioglycosides of Sialic Acids in Acetonitrile 359... 

Since 1965, a number of attempts for obtaining sialyl glycosides have been achieved [15,16], mainly by the classic Koenigs-Knorr method using Al-acetylneuraminyl halides 2 as glycosyl donors. However, the yield and stereoselectivity of the glycosides with sugar... 

In the following section, our recent development of the regio- and a-stereoselective sialyl glycoside syntheses using thioglycosides of sialic acids in acetonitrile is described. 

II. REGIO- AND a-STEREOSELECTIVE SIALYL GLYCOSIDE SYNTHESES USING THIOGLYCOSIDES OF SIALIC ACIDS IN ACETONITRILE... 

Figure 2 An efficient regio- and a-stereoselective synthesis of mono-sialyl glycosides. (SE = —CH2CH2SiMe3.)...

Figure 3 An efficient regio and a-stereoselective synthesis of oligo-sialyl glycosides.

Facile and highly regio- and a-stereoselective sialyl glycoside syntheses have been achieved by using, as glycerol donors, the 2-thioglycosides (11-13) of NeuSAc or... 

Particularly annoying is the competitive elimination which results from the deoxy center at C-3, giving the 2,3-dehydro derivative 7 as the major by-product. As critical problems, there are several disadvantages to the stereoselective synthesis of a-sialyl glycosides ... 

A. Kanoeyama, H. Ishida, M. Kiso, and A. Hasegawa, Stereoselective synthesis of sialyl-lactotetraosylceramide and sialyl neolactotetraosylcermide, Carbohydr. Res. 200 269 (1990). K. P. Ravindranathan and H. J. Jennings, A facile, one-step procedure for the conversion of 2-(trimethylsilyl)ethyl glycosides to their glycosyl chlorides. Tetrahedron Lett. 37 2537 (1990). 

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