Glycosyl donor phosphite

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. 

Several methods were reported for the selective synthesis of a-glycosides in the absence of a controlling group at C-2. The 2-deoxy sugar is first converted into a glycosyl donor by formation of phosphites,53 phophonodithioates,54 or phosphinothioates,55 which react with different acceptors and promoters. 

More recently, Schmidt et al. [102] reported the use of fully benzoylated fructofuranose phosphites as effective glycosyl donors. Very high glycosylation yields were obtained. As for the stereochemical outcome, the authors claim that, with unhindered primary acceptors, the a-linked fructofuranosides were obtained exclusively, but with more hindered alcohols the linked saccharide was also formed, in some examples as the sole product. This phenomenon, formation of the ds-product in spite of the use of a participating group, was discussed in Sect. 2.4. However, since no carbon and only selected proton NMR values are reported, it is not clear from the publication of Schmidt how the anomeric configuration of the fructofuranosides has been determined. This is not trivial, since in a fructofuranoside there is no anomeric proton and thus neither proton-proton nor carbon-proton coupling constants can be used. 

Watanabe, Y, Nakamoto, C, Yamamoto, T, Ozaki, S, Glycosylation using glycosyl phosphite as a glycosyl donor. Tetrahedron, 50, 6523-6536, 1994. 

Hashimoto, S, Umeo, K, Sano, A, Watanabe, N, Nakajima, M, Ikegami, S, An extremely mild and stereocontroUed construction of l,2-/ra w-p-glycosidic linkages capitalizing on benzyl-protected glycopyranosyl diethyl phosphites as glycosyl donors. Tetrahedron Lett., 36, 2251-2254, 1995. 

As certain types of glycosyl donors (such as glycosyl bromides, trichloroacetimidates and phosphites) are too reactive to withstand glycosylations, they cannot be used as acceptors. Consequently, they are used as type 1 donors in this strategy. However, other types of common... 

---