1,1 -disaccharide bridge

The 1,3-dipolar cycloaddition of exocyclic methylenes with nitrile oxides has already been addressed in section 2.13.10 This work, shown in Scheme 8.4.2, is notable in that high stereoselectivity in the resulting isoxazoline can be obtained. This is presumably the consequence of the bulk of the nitrile oxide directing approach to the a face of the sugar methylene. Through the use of these reactions, C-disaccharides, bridged by isoxazoline rings have been made accessible. 

Figure 9 Stereo view of an instantaneous neocarrabiose conformation taken from an MD simulation in aqueous solution, showing a water molecule hydrogen-bonding to both rings of the disaccharide, bridging between them and stabilizing the experimental conformation. Reprinted from Ref. 50 by permission from Wiley...

Among 132, a methylene-bridged disaccharide 132a was obtained when the intermediate 131 was allowed to react with ketone 133 (precursor of the starting chlorohydrin 130). 

On the other hand, when intermediate 266 reacted with the ketone 270 (precursor of epoxide 263), a methylene-bridged disaccharide 271 was the only reaction product isolated in low yield (15%), due to difficulties in its purification by column chromatography. 

Reactions in the second stage occur when precursor units move along the cytoplasmic membrane. In the first reaction, the M-acetylmuramylpentapeptide region binds (through a pyrophosphate bridge) to a carrier phospholipid that is bound to the cytoplasmic membrane. M-acetylglucosamine is then bound, forming a disaccharide-pentapeptide-P-P-phospholipid. 

R. R, Schmidt and R. Preuss, Synthesis of carbon bridged C-disaccharides, Tetrahedron Lea. 30 3409 (1989) B. Giese, M. Hoch, C. Lamberth, and R. R. Schmidt, Synthesis of methylene bridged C-disaccharides, Tetrahedron Lett. 29 1375 (1988). 

A disaccharide is a compound that is formed from two monosaccharide units by elimination of one molecule of water. At least one carbon atom involved in the acetal bridge (called glycosidic linkage)... 

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