2-thioglycosides

The following discussions consider the 1-thioglycosides and 1-thio sugars from the standpoint of synthesis and general reactions. Other thio sugars are particularly considered from the synthetic aspect. 

In this Section, the naturally occurring 1-thio-D-glucosides are discussed first. Chemically synthesized 1-thioglycosides and their reactions are then considered. Other iS-substituted derivatives of the 1-thio sugars, which normally react by cleavage of the /S-substituent to give the free 1-thio-aldoses, are treated in Section III (p. 152). 

Further evidence for structure (2) has been obtained for sinigrin, and for the glucosinalbate ion (2, R = P-HOC6H4CH2—) which is obtained as sinalbin from yellow mustard (Sinapis alba). For example, sinigrin, on treatment with Raney nickel, yields n-butylamine. Furthermore, acid 

The extensive investigations of Kjser and coworkers have revealed many new mustard-oil glucosides (see Table I) the findings of this group 

Glucobenzsisaustricin Sisymbrium austriacum Jacq. CsHsCO-OCHsCH (CsHb)- 27 

Synthesis and Activation of Carbohydrate Donors Thioglycosides and Sulfoxides 

Centre for Carbohydrate Chemistry, School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, UK 

A number of methods are available for preparing thioglycosides, those utilising per-(9-acetylated carbohydrates or acetylated glycosyl halides as the starting material being the most popular (for a summary of methods available see Table 4.1) [3,6,10]. 

Best Synthetic Methods Carbohydrates 2003 Elsevier Science Ltd. All lights reserved. 

The method of choice will depend upon the type of thioglycoside, namely, alkyl- or arylthioglycoside, which is to be prepared. Methods satisfactory for the preparation of both of these types of thioglycosides are outlined below. 

SCHEME 3.14 One-pot assembly of a trisaccharide using thioglycosides as donors. Bz, benzoyl Tol, 4-tolyl. 

SCHEME 3.15 Synthesis of disaccharide 33 using glycosyl sulfoxide. Piv, pivaloyl. 

Replacement of the exocyclic anomeric oxygen atom in a glycoside by sulfur or selenium produces the corresponding 1-thio- or a 1-seleno-glycoside. Certain 1-thioglycosides occur in Nature and others are important as glycosidase inhibitors.98-100 

A major use for 1-thio- and 1-seleno-glycosides is in the synthesis of O-linked glycosides and oligosaccharides.101 

Reaction of the tetra-O-acetyl-1 -thiopyranosc with an alkyl bromide or iodide yields an alkyl-1-thioglycoside. This method is particularly useful when the appropriate thiol is not available.121122 

1 2-ds configuration not normally obtained by the foregoing methods, and also, 

Similarly, reaction of a thioglycoside with a hydroxylic compound in the presence of an excess of a tetraalkylammonium bromide and the thiophilic promoter dimethyl(methylthio)sulfonium triflate (DMTST) proceeds with high stereoselectivity.131-133 

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

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. 

Partial hydrolysis of dithioacetals has been found useful for the preparation of anomers not obtained by the foregoing methods and also for preparation of fu-ranosidic 1-thioglycosides. 

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... 

Glycosylation of thioglycosides.1 1-Thioglycosides when activated with 1.5 equiv. of C,H,SeOTf, prepared in situ from QH SeCl and AgOTf, react at 0° to -40° with alcohols to form glycosides in 60-95% yield. The reaction is generally p-selective. 

Such a synthesis is shown in Scheme 4.18a, in which a glycosyl bromide is coupled with the thioglycosyl acceptor to afford a thioglycosyl disaccharide. The glycosyl bromide was obtained from the corresponding 1-thioglycoside by treatment with Br2. It was shown [222-224] that phenyl selenoglycosides can be selectively activated in the... 

In- the preceding section the reductive desulfurization of some substances which are both thioglycosides and thioacetals has been mentioned here the hydrogenolysis of the simple 1-thioglycosides will be discussed. 

The strong interest in 1-thioaldoses and 1-thioglycosides (66,201) as a consequence of their recent use as anomeric protecting-groups, and concomitantly for glycosyl transfer with the help of thiophilic activators, led to... 

Thioglycosides can be activated by a wealth of strategies,3,4 although our investigations center on the use of electrophilic iodine (7V-iodosuccinimide). 

The binding of chromophoric 1-thioglycosides from lactose or cellobiose to CBH I (Tr. r.) was followed by difference spectrophotometry of the ligand, or by the diafiltration technique (Fig. 4). Alternatively, perturbation of the protein spectrum could be used in the case of non-chromophoric ligands (Fig. 5). 

M. L. Wotfrom and W. Groebke, Tetra-O-acylglycosyl chlorides from 1 -thioglycosides and their conversion to penta-0-acyl esters, J. Org. Chem. 28 2986 (1963). 

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). 

The 1-thioglycosides have been reviewed in detail by Hortoh and Hutson the present Section deals only with the 1-thioaldofuranosides, mostly in relation to their preparation from dithioacetals. 

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