Phosphites, glycosylation

Thus, far, Kdo phosphite glycosyl donors have found only very limited interest The dihenzylphosphite Kdo donor 172 had heen prepared hy Ichiyanagi et al. by reaction of the hemiketal 42 with diben l N,N-diisopropylphosphoramidite and l//-tetrazole in 56% yield. Subsequent glycosylation reactions with diol 47, to produce disaccharide 48, were catalyzed either by TMSOTf or equimolar BF3 Et20 but gave poor yields and anomeric selectivities (Scheme 26). 

Salicylic acid was used for phosphite protection in the synthesis of glycosyl phosphites and phosphates. This derivative is very reactive and readily forms a phosphite upon treatment with an alcohol or a phosphonic acid upon aqueous hydrolysis. ... 

An innovative approach towards glycosyl phosphoramidites, which can be subsequently converted into the corresponding phosphite triesters,... 

The synthesis of the same trisaccharide core also illustrated the orthogonality between glycosyl phosphite and phosphoroamidate donors as well as between an... 

Intriguing approaches have been developed using mannosyl fluorides,30,31 phosphites,32 and thioglycosides (Scheme 7.8).33 However, their generalities, particularly in terms of applicability to complex and biologically relevant systems, are yet to be clarified. Quite probably, the most successful donor for direct P-mannosylation is the sulfoxide developed by Crich and coworkers (Scheme 7.9).34-37 Glycosyl sulfoxides were originally developed by Kahne and have proved... 

T. Muller, G. Hummel, and R. R. Schmidt, Glycosyl phosphites as glycosyl donors. A comparative study, Liebigs Ann. Chem. p. 325 (1994). 

T. J. Martin and R. R. Schmidt, Efficient sialylation with phosphites as leaving group, Tetrahedron Lett. 33 6123 (1992) T. J. Martin, R. Brescello, A. Toepfer, andR. R. Schmidt, Synthesis of phosphites and phosphates of neuraminic acid and their glycosyl donor properties— convenient synthesis of GM3, Glycoconjugate J. 70 16 (1993), and references therein. 

T. MUIIer, R. Schneider, and R. R. Schmidt, Utility of glycosyl phosphites as glycosyl donors— fructofuranosyl and 2-deoxyhexopyranosyl phosphites in glycoside bond fonnation, Tetra-nedron Lett. 35 4763 (1994). 

A relatively new method, this involves glycosyl phosphites as glycosyl donors (Scheme 6). Independently reported by Schmidt [18] and Wong s groups [19], this method has already found important applications in the synthesis of sialyl derivatives [19]. 

This reaction mechanism could be applicable to the method employing xanthate (6) or phosphite (7) as the glycosyl donor in acetonitrile medium. 

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