O-Galactosyl trichloroacetimidates

For the galactosylation reactions, 2,3,4,6-tetra-O-benzylgalactopyranosyl trichloroacetimidate 2 and dibenzylphosphite 10 were used as donors (Table 12.1). Under these conditions, the (5-(l—>3)- and (5-(l—>4)-linked disaccharides 16 and 17 were formed in only minor amounts (entries 1 and 2). To increase the proportion of the (5-anomers, the peracetylated galactopyranosyl trichloroacetimidate 11 was used as the donor. Reactions were poor in DMF, but in dioxane, a clean mixture of products was obtained. Two equivalents of donor were required to give a conversion of 20-30% of 1 to disaccharides 13-18. Peaks eluting when the column was washed with more polar solvent mixtures suggested that only traces of trisaccharides were formed, but the identity of these peaks was not investigated. 

TABLE 12.1 Use of 2,3,4,6-Tetra-O-benzylgalactopyranosyl Trichloroacetimidate and Dibenzylphosphite in Galactosylation Reactions... 

Novel branched yS-CyDs with jS-o-galactose residues were chemically synthesized using the trichloroacetimidate method. Tetraacetyl galactosyl trichloroacetimidate was obtained with trichloacetonitrile in the presence of l,8-diazabicyclo[5.4.0] undec-7-ene (DBU) [101]. 

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