1-Thiols, thioglycosides preparation

Thiols, thioglycosides preparation, 183 2,3,4-Tri-O-ethylamylose, structure, 412 Triple bonds, unsaturated monosaccharides, 95-96... 

Thioglycosides have been prepared on solid phase by glycosylation of thiols with various types of glycosyl donor. Carbohydrate-derived thioethers have been used either to link carbohydrates to thiol-functionalized supports [9,26,78,79] or as glycosyl donors for the preparation of glycosides on solid phase (see Section 16.3.3). 

Early studies employing hydrogen chloride as catalyst on perbenzoylated sugars showed complicated product mixtures [1,30], while Lewis acid-catalyzed mercaptolysis of peracetylated monosaccharides afforded the corresponding thioglycosides in good yields [31,32,33], However, from a preparative point of view (smell, work-up), the present use of a solvent and only a small excess of thiol is definitely an advantage. 

Addition of thiols to Michael acceptors is another classical reaction that has been used extensively to produce thioglycosides from the corresponding thioaldose nucleophile (O Scheme 44 and Scheme 48) [150,160]. Both monosaccharide and oligosaccharide thioglycosides (compare O Scheme 59) have been prepared. 

Catalytic cross-coupling reactions were shown to be of much help in preparing several important compounds. For example, thiazene-substituted thioglycosides were readily synthesized via the reaction of the corresponding thiols with aryl iodides in the Cul/Py catalytic system in MeCN (Scheme 3.39) [69]. 

Synthetic thioglucosides are prepared by the action of thiophenol on acetylglycosyl bromides in the presence of sodium hydroxide (71,72). They are extremely resistant to acid hydrolysis, and this resistance probably explains the lack of hydrolysis by almond emulsin (71,73). By treatment of sugar thiols with mercuric chloride, thioglycosides also may be synthesized (Chapter V) ... 

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