Glycosylations silver® trifluoromethanesulfonate

T. Ziegler, P. Kovac, and C. P. J. Glaudemans, Transesterification during glycosylation promoted by silver trifluoromethanesulfonate, Liebigs Ann. Chem. p. 613 (1990) and references cited therein. 

In relation to carbohydrate chemistry, the Koenigs-Knorr synthesis of glycosides involves the treatment of glycosyl halides with an alcohol or phenol in the presence of a heavy metal salt.267 Karrer268 discovered that reaction of silver salts of hydros acids could also be used and use of these reagents has been extended more recently. Numerous variations and improvements on the original method have now been reported, and silver oxide, silver carbonate or silver trifluoromethanesulfonate have since become the accepted standard reagents.267... 

The advances that have led to the almost routine synthesis of tri- and tetrasaccha-rides began in the early 1970s and included a new approach to a-glycosides, the halide-ion catalyzed glycosylation [4], and the introduction of improved heavy metal catalysts such as silver trifluoromethanesulfonate (triflate) [5]. Numerous other technical and conceptual advances punctuated the intervening period and reference to these developments are to be found in the cited literature of several reviews [6—9]. 

Douglas, S P, Whitfield, D M, Krepinsky, J J, Silver trifluoromethanesulfonate(triflate) activation of trichloroacetimidates in glycosylation reactions, J. Carbohydr. Chem., 12, 131-136, 1993. 

P. J. Garegg and T. Norberg, Observations on silver trifluoromethanesulfonate-promoted syntheses of 1,2-trans-glycosides from acylated glycosyl bromides, Acta Chem. Scand. B, 33 (1979) 116-118. 

Seibel et al. [36] reported, for the first time, the use of microwave heating in the glycosylation of amino acids. They performed glycosyl transfer reactions of perace-tylated monosaccharides (glucose and galactose) and disaccharides (maltose and lactose) with N-9-fluorenylmethoxycarbonyl-L-serine benzyl ester in the presence of iron trichloride with short reaction times (4 min, compared with 5-10 h by conventional heating) and with improved yields (52-61% compared with 10-31% by conventional heating). It is worthy of note that in these reactions heavy metal compounds, for example silver trifluoromethanesulfonate, mercury dibromide and di-cyanide, or boron trifluoride-diethyl etherate, can be replaced by the environmentally safe promoter iron trichloride. 

In addition the selective activation of both glycosyl trichloroacetimidates (using catalytic triethylsilyl trifluoromethanesulfonate at —78 °C) and glycosyl bromides (using silver trifluoromethanesulfonate and collidine) over selenoglycosides can be achieved. 

Coupling of the glycosyl donor and acceptor takes place in the presence of silver tri-fluoromethanesulfonate (AgOS02CF3) as a source of Ag", which activates the pyranosyl bromide toward nucleophilic substitution. A weak base such as 2,4,6-trimethylpyridine is included in order to react with the trifluoromethanesulfonic acid that is produced in the reaction. 

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