Pentasaccharide trichloroacetimidate

In another application of catalytic glycosylation with triflic acid, two disaccharides were synthesized with donors bearing trichloroacetimidate function and then the disaccharides thus prepared were condensed in a similar manner to a tetrasaccharide757 (1,2-dichloroethane, 55°C, 1.5 h, 50-85% yields). The same protocol was used in the synthesis of a decasaccharide from mono-, tetra-, and pentasaccharide building blocks.758 The trichloroacetimidate procedure has been successfully used in the glycosylation of /3-cyclodextrins promoted by triflic acid.759 760... 

As illustrated, the pentasaccharide is synthesized from the trichloroacetimidate building blocks (224-226). To avoid problems in the synthesis of the critical (3-D-mannosidic linkage in the solid phase, this bond was incorporated into the disaccharide building block 225, which was prepared... 

A convergent synthesis of the pentasaccharide derivative 33 of the triterpeniod saponin obtained from the plant Spergularia ramosa was achieved as outlined in Scheme 6 68 The entire assembly relied on use of the trichloroacetimidate protocol and was accomplished in a three plus two fashion. The assembly of the trisaccharide was initiated by the glycosidation of glucosyl trichloroacetimidate donor 22 with rhamnosyl diol acceptor 23 to provide disaccharide 24 in 63% yield. The latter could be used directly as the glycosyl acceptor for the reaction with xylosyl donor 25, leading... 

Iadonisi and coworkers developed a clever block-synthesis approach to the antitumor a-(l >3)-pentamannan known as PI-88, illustrating the selective activation of a trichloroacetimidate 43 in the presence of a /V-phenyl trifluoroacetimidate 44 (Scheme 10).12 This useful selectivity enabled assembly of the complete pentasaccharide with the adjustment of only a single protecting group in the course of the entire sequence. 

More recently, the trichloroacetimidate strategy has been applied to the synthesis of a branched pentasaccharide unit common to most complex Af-glycan structures (Scheme 10). Reaction of marmosyl donor 57 with thiol-functionalized resin resulted in attachment to the polymer matrix through the reducing end of the sugar... 

Figure 18 Solid-phase synthesis of pentasaccharides using trichloroacetimidates.

Solid phase technology and use of 6-0-acetyl-2,3,4-tri-0-benzyl-a-D-glucosyl trichloroacetimidate led to (1 - 6)-linked pentasaccharides. ... 

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