0-Glycosyl imidates

Glycoside Synthesis from 1-Oxygen-Substituted Glycosyl Imidates 143... 

In 1983, Schmidt reported another type of glycosyl imidates, trifluoroacetimidates... 

This review covers the recent advances in the use of O-glycosyl imidates in oligosaccharide and glycoconjugate synthesis, with emphasis on literature published between 1999 and 2006. However, because of the large volume of work in this area, only the most representative applications will be presented. One can refer to the similar preceding review [381] published in 2000 and another quite comprehensive review [375] on trichloroacetimidate method published in 1994 for earlier application of glycosyl trichloroacetimidates. Trifluoroacetimidate method will be discussed separately in this review in the light of its less popularity in carbohydrate chemistry. 

Glycoside Synthesis from 7-Oxygen-Substituted Glycosyl Imidates 145... 

Glycoside Synthesis from i-Oxygen-Substituted Glycosyl Imidates 175... 

The problem of the nucleophilicity of amides in glycosylation reactions is not limited to the sulfoxide method and has been shown to result in the formation of glycosyl imidates from intermolecular reaction with activated donors. It appears that this problem may be suppressed by the prior silylation of the amide [348,349]. Accordingly, it may be sufficient to operate the sulfoxide method with an excess of triflic anhydride when amides are present so as to convert all amides into O-triflyl imidates, which are then hydrolyzed on work-up. Despite these problems, several examples have been published of successful sulfoxide glycosylation reactions with acceptors carrying remote peptide bonds [344,345] and with donors coupled to resins via amide-based linkages [346,347], with no apparent problems reported. Sulfonamides and tertiary amides appear to be well tolerated by the sulfoxide method [340,350],... 

Other Glycosyl Imidates, Glycosyl Carboxylates, and Glycosyl... 

Scheme 18 Synthesis of the Core 1 (T-Antigen) Structure Using the Glycosyl Imidate[2781...

Mahlin, J.A., Jung, K.H., and Schmidt, R.R., Glycosyl imidates, synthesis of flavone C-glycosides vitexin, isovitexin and isoembigenin, Liebigs Ann. Chem., 3, 461, 1995. 

R. R. Schmidt and J. Michel, Facile synthesis of a- and [3-f7-glycosyl imidates preparation of glycosides and disaccharides, Angew. Chem. Int. Ed. Engl. 79 731 (1980). 

The coupling protocols described in the two previous examples can be combined to allow for the synthesis of branched carbohydrates.19 The automated solid-phase synthesis of a tetrasaccharide is illustrated in Scheme 4. Both glycosyl phosphate and glycosyl imidate building blocks were used along with acetate and levulinate esters as temporary protecting groups. 

Grundler, G. and Schmidt, R. (1984) Glycosyl imidates, 13. Application of the trichloroacetimidate procedure to 2-azidoglucose and 2-azidogalactose derivatives. Liebigs Ann. Chem., (11), 1826-1847. 

SCHEME 6.28 Mong s stereoselective one-pot synthesis using DMF as the novel additive to facilitate the 1,2-as-glycoside formation, (a) The glycosyl imidates formed with DMF. (b) The one-pot synthesis of trisaccharide 142. 

---