Glycosyl groups, active

Glycosyl group Activated form With a-linked sugar With linked sugar Total number... 

Apart from glycosyl acetate and benzoate donors, more elaborate O-carbonyl derivatives offer potential for distinct modes of anomeric leaving group activation. Many of these donors (Scheme 3.21) involve activation of an anomeric O-carbonyl derivative 134 at a remote functional group (Y). The adivated remote functionality, in turn,... 

The presence of strongly nucleophilic groups in either the donor or the acceptor can be problematic in sulfoxide-type glycosylations when activation is conducted with triflic anhydride. The most common culprit is the amide group [340,341], which is illustrated by the formation of a dihydrooxazine when a 3-acetamido alcohol was employed as acceptor (Scheme 4.47) [342]. Self-evidently, acceptor-based problems of this type could be avoided by the preactivation of the sulfoxide with triflic anhydride. 

Further studies will be needed in order to resolve the intriguing question as to how the glycosyl groups of the activated sugars that are usually found in the cytoplasm are transferred to the growing chain of the lipid-bound oligosaccharide inside the lumen of the endoplasmic reticulum. 

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