Glycosyl anomeric protecting groups

The strong interest in 1-thioaldoses and 1-thioglycosides (66,201) as a consequence of their recent use as anomeric protecting-groups, and concomitantly for glycosyl transfer with the help of thiophilic activators, led to... 

The 2-(trimethylsilyl)ethyl group (TMSEt) has found widespread use as anomeric protecting group.49 It can be introduced by a glycosylation (see Chapter 4) and cleaved by treatment with BF3 Et20. The mechanistic considerations of the latter cleavage are as follows a hard base such as a... 

CONTROLLING ANOMERIC SELECTIVITY, REACTIVITY, AND REGIOSELECTIVITY IN GLYCOSYLATIONS USING PROTECTING GROUPS... 

More specific anomeric protecting groups are the 2-trimethylsilylethyl (TMSE) [25] and p-methoxyphenyl glycosides [26], both introduced by glycosylation reactions on protected derivatives (Scheme 3.5). The former is cleaved by treatment with BF3-etherate conditions in which TBDMS ethers survive. p-Methoxyphenyl glycosides are cleaved by CAN-oxidation similarly to p-methoxybenzyl ethers. 

Pleuss, N, Kunz, H, A-Glycosyl amides removal of the anomeric protecting group and conversion into glycosyl donors, Angew. Chem. Int. Ed., 42, 3174-3176, 2003. 

Other uses for glycosylamides have also been described in the literature. Amphiphilic glycosylamides have been demonstrated to be a valuable class of non-ionic biosurfactants (/O). Also, Kunz has used N-glycosylamides as an anomeric protecting group in glycosylation sequences (4). 

Dipolar addition of ethyl propiolate to the nitrile oxide 285, prepared by chlorination of the corresponding oxime, gave, after removal of protecting groups, the C-glycosyl-isoxazole205 (286). These reactions further demonstrate the utility of anomerically functionalized C-/3-D-ribofuranosyl derivatives that can be prepared from the versatile aldehyde 100. 

Several methods are available to access glycosyl iodides (Scheme 2.50). Anomeric hemiacetals bearing diverse protecting groups (Bn, Bz, Ac, N3, CMe2) upon treatment with a polymer-bound triphenylphosphine-iodine complex and imidazole can be converted into a-glycosyl iodides [179]. The precipitated by-products,... 

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