Hydroxy Sugars

The transformation of 1-hydroxy sugars to the corresponding glycosyl fluorides can be achieved by a mixture of Selectfluor 3 (Figure 2.2) and methyl sulfide presumably through a fluorosulfonium ion 9, which then reacts with the anomeric... 

T. Mukaiyama, Y. Hashimoto, Y. Hayashi, and S.-l. Shoda, Stereoselective synthesis of a-ribonucleosides from 1-hydroxy sugars by using 2-fluoropyridinium tosylate, Chem. Lett 557 (1984). 

A mixture of Yb(OTF)3 and methoxyacetic acid is used as a catalyst for the reaction of 1-hydroxy sugar with alcohols to form glycosides. The glycosylation in general is stereoselective. 

Suda, S, Mukaiyama, T, Stereoselective synthesis of l,2-tran5-ribofuranosides from 1-hydroxy sugars by the use of [l,2-benzenediolato(2-)-0,6y]oxotitanium and trifluoromethanesulfonic anhydride, Chem. Lett., 431-434, 1991. 

Inanaga, J, Yokoyama, Y, Hanamoto, T, Catalytic O- and 5-glycosylation of 1-hydroxy sugars, J. Chem. Soc. Chem. Commun., 1090-1091, 1993. 

Susaki, Ft, Glycosidation with 1-hydroxy sugars as glycosyl donors promoted by trimethylsilyl chloride and zinc triflate, Chem. Pharm. Bull., 42, 1917-1918, 1994. 

Mukaiyama, T, Matsubara, K, Hora, M, An efficient glycosylation reaction of 1-hydroxy sugars with various nucleophiles using a catalytic amount of activator and hexamethyldisiloxane. Synthesis, 1368-1373, 1994. 

Table 3.6 Glycosylations of 1-hydroxy sugars in an acid-IL under reduced pressure...

Toshima K, Nagai H, Matsumura S (1999) Novel dehydrative glycosidations of 1-hydroxy sugars using a heteropoly add. Synlett 9 1420-1422... 

Chapter 3 demonstrates the development of environmentally benign 0- and C-glycosylation methods using glycosyl phosphates, glycosyl fluorides, methyl glycosides, and 1-hydroxy sugars in several ionic liquids. 

Finally, the activation at the anomeric position through the Mitsunobu reaetion will be considered. Besides the 1-hydroxy sugars, the 1-O-silylated glycosides used as glycosyl donors will also be included in this section. 

Several other attempts to activate 1-hydroxy sugars with cationic activators or Lewis acid catalysts have appeared in literature, in which a second active species is generated in situ by additional reagents. 

A particular method for the anomeric activation of 1-hydroxy sugars is the Mitsunobu reaction which has mainly found application for the synthesis of aryl glycosides. Following from an earlier publication [66], Garegg described [67] the use of this reaction for synthesis of aryl p-o-mannopyranosides. Lubineau studied [68] the influence of the pKa of the acid or phenol in the formation of aryl and acylglyco-sides derived from three pesticides. 

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