Orthogonal scheme oligosaccharides

Scheme 4.86 Orthogonal thioimidate-based, one-pot oligosaccharide synthesis [468].

Another hybrid protecting group is the p-[(trimethylsilyl)ethoxy]methoxy benzyl (p-SEM-benzyl) ether354 Phenolate anions generated by treatment of p-SEM-benzyl ethers with TBAF in DMF at 80 °C eliminate to give the deprotected alcohol as illustrated in Scheme 4.303 p-SEM-benzyl ethers are compatible with many of the standard manipulations in oligosaccharide synthesis and they arc orthogonal to benzyl and p-methoxybenzyl ethers. 

Scheme 5 Synthesis of oligosaccharides based on orthogonal glycosylations.

Scheme 7.1 Oligosaccharide assembly traditional concept (left) and by an orthogonal strategy (right).

For the synthesis of HA oligosaccharides, model glycosylations were carried out in solution and on PEG support. A glucosamine acceptor coupled with hydrojyl-terminated PEG monomethyl ether 11 was efficiently glycosylated with trichloroacetimidate donor 10 afford an orthogonally protected disaccharide 12 which can be used for the synthesis of HA sequences, see Scheme 3. 

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