Trichloroacetimidate approach

To date, heptasaccharide 47 is the largest oligosaccharide assembled on a solid support using only monosaccharide building blocks. This turns out to be an excellent demonstration of the efficiency of the (9-glycosyl trichloroacetimidate approach. 

A maltotetraoside 65 containing three 5-thioglucose units in the non-reducing positions was prepared by the Hashimoto group who exploited the trichloroacetimidate approach in a linear sequence of glycosylation steps [155],... 

The on-column synthesis approach was also explored, followed by in situ purification of the products for the glycosylation reactions using trichloroacetimidates. The authors primed the top of a standard silica chromatography column with perchloric acid immobilized on silica. After charging both reactants, dissolved in dry CH2C12, onto the... 

Trisaccharide 80 was synthesized by a similar approach, in which a rhamnoside was formed in 86% yield, transformed into its trichloroacetimidate, submitted to the second glycosylation step promoted by H2S04-silica (84% yield), and subsequently deprotected to 80.91... 

The synthesis of a 2 -amino-2 -deoxyuridine 168 and a 2 amino-2 deoxycytidine 169 from inexpensive uridine has been described. A key transformation in the synthesis is the introduction of an amino functionality via a trichloroacetimidate. This approach also avoids the use of azide that is not desirable for large-scale use (Scheme 8.48). 

A comparison of direct O-mannosylation of serine or threonine on resin-bound peptides, with the incorporation of mannosylated serine or threonine building blocks, resulted in a higher overall yield for the building block approach (12.5 vs 5% for direct condensation). 134 Later it was demonstrated that resin-bound peptides are able to be glycosylated with different glycosyl trichloroacetimidates without protection of the hydroxy groups of the oligosaccharide moiety (Section 6.3.2.8). 135,136 ... 

The notion of glycoside synthesis with unprotected glycosyl donors [10] has instigated the exploration of some new approaches using the trichloroacetimidate group [15], electrochemistry [16], electron transfer [17], and Lewis acid catalysis [18], The scope of applicability of these newer methods remains to be tested. 

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