Glycosylation 1-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... 

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. 

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. 

K. S. Kim, D. B. Fulse, J. Y. Baek, B.-Y. Lee, and H. B. Jeon, Stereoselective direct glycosylation with anomeric hydroxy sugars by activation with phthalic anhydride and trifluoromethanesulfonic anhydride involving glycosyl phthalate intermediates, J. Am. Chem. Soc., 130 (2008) 8537-8547. 

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

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. 

Example an heteropoly acid act both as promoter and dehydrating agent in the glycosylation of an anomeric hydroxy sugar donor... 

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. 

Trichloroacetonitrile reacts with glycosidic hydroxy groups of protected sugars to form glycosyl trichloroacetimidates (R. R. Schmidt, 1980, 1984,1985,1986 B. Wegmann, 1988). The imidate is substituted by alcohols in the presence of trimethylsilyl trifluoromethanesulfonate... 

Stabilities and colors of anthocyanins are dependent on the nature and number of sugars attached to the flavylium ion and the nature and number of acids linked to the glycosylic moiety. Tint and hue, however, are related to the numbers and positions of hydroxyl and methoxyl substituents in the flavylium ion. In addition, 3-deoxy-anthocyanins that are yellow due to dehydroxylation of the carbon at C-3 have higher stabilities than the corresponding 3-hydroxy anthocyanins that in turn are red but lose much of their stability. 

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