Alkyl thioglycosides

Carbohydrate derivatives with anomeric sulfur are not very common in nature, the only examples found are the various glucosinolates ( mustard oil glycosides ) mainly from the Bras-sicaceae family [1,2,3], the simple alkyl thioglycosides of lincomycin and structurally relat-... 

A variety of l,2-m 5-glycopyranosyl esters have been prepared in high yields and with excellent selectivity by reaction of alkyl thioglycoside derivatives with carboxylic acids in the presence of -iodosuccinimide. An example is given in Scheme aP 1,2-rra/w-Glycosyl acetates are available from methyl a- or -thioglycopyranosides by treatment with acetic... 

In the field of sialic acids compound 58 has been derived by appropriate additions to the 2,3-ene and appears to be a potentially important sialylating agent giving almost 100% a-selectivity several appropriate disaccharides and trisaccharides were made. From the 3-deoxy-2-acetylthio derivative several S-alkyl thioglycosides have been made by treatment with the alkyl bromides in alkaline conditions. Synthesis of the thiocoumaryl a-glycosides 59 was effected to afTord potential fluorogenic substrates for sialidases. ... 

In contrast, cleavage of alkyl and also aryl thioglycosides with dimethyl(meth-ylthio)sulfonium tetrafluoroborate takes place with total inversion of configuration [9] (equation 12) The latter reagent is commercially available or easily prepared as a crystalline nonhygroscopic solid [10]. All the three above-mentioned reagents... 

A great variety of methods for the preparation of alkyl and aryl 1-thioglycosides of aldoses have been described30-31 ... 

Fully acetylated hexopyranoses react with thiols in the presence of Lewis acids, such as BF3-Et20.32,33 The reaction is faster with 1,2-trans acetates than with the corresponding 1,2-cij ones and 1,2-trans products predominate. Alkyl, alkenyl, and aryl thioglycosides are produced by this method. Variations on this method include the use of trimethylsilyl34 or stannyl derivatives35 of the thiols. 

In this classic41 and general method, an acylated glycosyl halide reacts with a thiolate anion to produce a 1-thioglycoside, usually with 1,2-trans configuration. With alkyl thiolates, re-acylation is normally required following this treatment. 

Acylated glycosyl thiocyanates are made by treatment of acylated glycopyranosyl halides with potassium thiocyanate.30 Reaction at —40° with a Grignard reagent affords alkyl or aryl 1-thioglycosides.54... 

Acetylated 1-thioaldoses react with alkenes in the presence of azobis(isobuty-ronitrile) (AIBN) to give acylated alkyl 1-thioglycosides.55... 

Mechanistic studies [123] have shown that thioglycosides can undergo in situ anomerization in the presence of iodonium ion catalysts. It has been demonstrated that this anomerization proceeds by intermolecular exchange of alkyl thio groups. An increase in the steric bulk of the leaving group resulted in incomplete or no anomerization. It has been proposed that this anomerization process is important for the stereochemical outcome of glycosylations [123]. 

Carbohydrate derivatives, in which one or more of the oxygen atoms bonded directly to the carbon skeleton have been replaced by sulfur, are termed thiosugars. The placement of the sulfur atom at the anomeric position constitutes a special case, because thioglycosides, alkyl, aryl and heterocyclic, occupy a very important place as versatile glycosyl donors in glycosidation methodology. Anomeric thiocarbonyl compounds, on the contrary, have been less explored, although their potential and scope is likely to be similar. 

S. Hanessian and Y. Guindon, Chemistry of the glycosidic linkage. Direct conversion of glycosides into 1-thioglycosides by use of [alkyl (or aryl)thio] trimethylsilanes, Carbohydr. Res. 86 C3 (1980). 

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