Sialylated galactose disaccharide

Investigations of the influence of the hydroxy groups in the acceptor galactose ring on the trans-sialylation showed that the 2- or 6-deoxy, or even the replacement of /1-Gal by /l-i.-Ara, did not impair the reaction, although a lower yield (30%) was obtained with the fucose disaccharide.165... 

As a representative example, Paulsen and Von Reessen used a sialyl bromide to apply the Koenigs-Knorr method to the synthesis of an a-2,3-linked disaccharide (Scheme 8) [7b]. Glycosylation of the galactose acceptor 19 with sialyl bromide 18 led to the desired disaccharide 20, although with poor stereoselectivity (ca. 1 1 a j8). The low yields of Koenigs-Knorr glycosylations with secondary alcohols are partly due to elimination of the sialyl halide and formation of the 2,3-dehydro derivative 21. 

The decisive role of the exo-anomeric effect in the conformational behaviour of interglycosidic linkages has been demonstrated by molecular dynamics and molecular mechanics studies on the preferred solution conformations of eight C-linked D-glucosyl disaccharides,of the C-linked disaccharide 5 together with its natural 0-linked equivalent 6, " and of the two isomeric hydroxymethylene-linked analogues of sialyl-a-(2- 3)-D-galactose. ... 

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