Sialic acid thioglycosides

Fig. 6 The relative reactivity values (in parentheses) of sialic acid thioglycosides...

Several ganglioside analogs containing an a-thioglycoside of sialic acid, derived for example from (29 c) (Scheme 8), have been found to be potent inhibitors of sialidase activities of different subtypes of influenza virus [64]. 

II. Regio- and a-Stereoselective Sialyl Glycoside Syntheses Using Thioglycosides of Sialic Acids in Acetonitrile 359... 

In the following section, our recent development of the regio- and a-stereoselective sialyl glycoside syntheses using thioglycosides of sialic acids in acetonitrile is described. 

II. REGIO- AND a-STEREOSELECTIVE SIALYL GLYCOSIDE SYNTHESES USING THIOGLYCOSIDES OF SIALIC ACIDS IN ACETONITRILE... 

The lactonized phenyl 2-thioglycosides of dimeric (26) [41] and trimeric (27) [42] sialic acids, which were prepared from the corresponding oligosialic acids according to the procedure employed for the monosialyl derivatives, were each coupled with the suitably protected sugar acceptors (14, 16, 17, and 19) by use of NIS-TfOH as a promoter in acetonitrile, as just described for the monosialyl glycoside synthesis (Fig. 3). 

Notes and discussion. This reaction can be utilized for the preparation of a-allyl, ethyl, phenyl and substituted aryl thioglycosides of sialic acid. NMR and NMR spectra of the crude reaction mixtures have confirmed that complete anomeric inversion occurs under the PTC condition. Adoption of tetrabutylammoniumhydro-gen sulfide as a PTC is critical for mild reaction conditions, otherwise, if triethylbenzylammonium chloride is employed, more harsh conditions are required. The use of ethyl acetate is advantageous over dichloromethane owing to the production of PhSCH2Cl and (PhS)2CH2 resulting from nucleophilic displacement of one or two chlorides of dichloromethane with thiophenol in the model experiment. 

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