Ethyl thioglycosides, glycosidation

Glycosylation with perbenzylated armed phenyl selenoglycoside 183 of the same glycoside acceptors (174,175, and 176) was efficient and an a/ j8 mixture of disaccharides 184, 185, and 186 was obtained (Table IV). Since a weak thiophilic promotor (IDCP) was employed in this case, glycosylation of armed ethyl thioglycoside acceptor 187 was also possible, affording an alfi mixture of 188 (Table V). 

Thioglycosides have received some attention over the last few years. The ethyl thio-glycoside 435 has been found to be a good substrate for the selective formation of the a-glycosyl cyanide 436 (Scheme 76) [127],... 

Some photoreactive CMP-neuraminic acids 32 have been prepared as substrates for a-(2- 6)-sialyltransferases, and synthesis of some thio-umbelliferyl glycosides of ulosonic acids is mentioned in Chapter 3. The ethyl thioglycoside 33 was prepared in 47% overall yield from neuraminic acid and used as a glycosyl... 

Scheme 2.71 Principle of "orthogonal glycosidic activation on a polymer (e.g. polyethylene glycol) support, lb facilitate purification, a hydrophobic tag (e.g. 2-(trimethylsilyl)ethyl) is introduced [158]. Conditions A are for thioglycoside activation, conditions B for activation of glycosyl fluorides.

Thioglycoside 13 (R = Bn, R = Et) was designed for delivering the ethoxy group to give the ethyl glycoside. When activation was effected, however, in the presence of the analogue 13 (R = OPmb, R = o-bromobenzyl) appreciable cross-over took place and led, for example, to o-bromobenzyl tetra-O-benzyl-D-... 

---