Galactosyl trichloroacetimidate donor

Hunt and Roush [60] used a solid phase method to prepare 6-deoxy di- and trisaccharides. A sulfonate linker was employed to coimect the first monosaccharide, a glycal, via its C6 position to the polymer resin. A galactosyl trichloroacetimidate donor was used in the first coupling reaction, followed by cleavage from the solid support by treatment with Nal to furnish pure disaccharides in 85-91% yield. Reduction with BusSnH (AIBN) provided the desired 6-deoxydisaccharide. 

The KRN7000 was synthesized from the galactosyl donor and the amide-type acceptor 52). In our initial synthesis of a-GalCer, we used the active armed trichloroacetimidate donor 1 and acceptor 2 under TMSOTf as a... 

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. 

High a-selectivities were observed when the D-galactosyl donor 10 was used for the coupling with secondary hydroxy groups in carbohydrate acceptors including 9 (see Scheme 5). With the trichloroacetimidate method [5], the yields of disaccharides derived from 6 and 7 were 85% (10 1, a/p) and 87% (only a), respectively. The condensation of 10... 

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