Trichloroacetimidates glycosyl donor

O-glycosidation between O-silylated glycosyl acceptors and several 1-substituted sugars, glycopyranosyl or furanosyl silyl ethers [79a], fluorides [80], phosphates [81], and trichloroacetimidates [82a] has been examined to develop other efficient and stereoselective procedures catalyzed by silicon Lewis acids. The trichloroacetimidate glycosyl donors are fairly reliable and were used for the synthesis of eanelioside GD by Ogawa (Fig. l)[82b]. 

These impressive initial accomplishments using trichloroacetimidate glycosyl donors on the solid support underscore the potential this strategy holds for the... 

GLYCOSYLATION. TRICHLOROACETIMIDATE GLYCOSYL DONORS R TEMPORARY PROTECTION... 

An example to demonstrate the versatility of trichloroacetimidates as glycosyl donors was reported by van Boom (Figure 6.3) [58]. In synthetic studies of the subcapsular polysaccharide C-substance 96 from Streptococcus Pneumoniae type 1, the targeted disaccharide unit 101 is efficiently prepared in 75 % yield with the trichloroacetimidate glycosyl donor 97. The corresponding thioglycoside donors 98 and 99 are less reactive and afford considerably lower yields of the desired coupled product. 

Trichloroacetimidates as glycosyl donors for generation of anomeric phosphates... 

Glycosyl donor Trichloroacetimidate formation Glycosyl acceptor0 Reaction conditions Reference... 

The great interest in C-glycosyl compounds is reflected in the extensive research in this field (204). Successful investigations with O-glycosyl trichloroacetimidates as glycosyl donors and phenol ethers (199,207,208), silyl enol ethers (205,206), trimethylsilyl cyanide (205,206), and allyltrimethylsi-lane (206) as C-acceptors underline the wide scope of these highly reactive glycosyl donors. 

The first application of (9-glycosyl trichloroacetimidates as glycosyl donors for the glycosylation of an acceptor attached to Merrifield resin was reported by our group in... 

Even controlled-pore glass (CPG) could be successfully employed as solid support with (9-glycosyl trichloroacetimidates as glycosyl donors. Thus, limitations of solvents and reaction temperatures in the glycosylation step, as experienced with the Merrifield resin, are restricted to those observed in solution-phase synthesis. Therefore, regio- and stereocontrol of the glycosylation reactions should be available from well-established solution-phase methodologies. 

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