Use of the [.beta.-(trimethylsilyl)ethoxy]methyl (SEM) protecting group in carbohydrate chemistry. Fully functionalized rhamnose acceptors and donors for use in oligosaccharide synthesis

The use of the [β-(trimethylsilyl)ethoxy]methyl (SEM) acetal as a protecting group in carbohydrate chemistry is described. The compatibility of this group with a variety of protection/deprotection conditions normally encountered in oligosaccharide synthesis is demonstrated, by way of example, with the preparation of fully functionalized rhamnose acceptors and donors and their subsequent use in glycosylation reactions. Thus, reaction of allyl 2-O-benzoyl-4-O-benzyl-α-L-rhamnopyranoside with SEM chloride resulted in a fully protected and functional key monosaccharide, namely allyl 2-O-benzoyl-3-O-[[β-(trimethylsilyl)ethoxy]methyl]-4-O-benzyl-α-L-rhamnopyranoside