Having a Sulfur- or Selenium-containing Hemiacetal Ring

Monosaccharides Having a Sulfur- or Selenium-containing Hemiacetal Ring 

For the introduction of sulfur into the sugar molecule, the nucleophilic replacement of a p-tolylsulfonyloxy group by an RS ion serves admirably. A comprehensive review of this reaction has appeared in this Series. From the derivatives so obtained, the sugar having the 

5-Thio-D-xylopyranose has been the sugar of this type most thoroughly investigated. Its synthesis was reported in 1961, independently and simultaneously from three different laboratories. With sodium thiocyanate, l,2-0-isopropylidene-5-0-p-tolylsulfonyl-a-D-xylofuranose (211) gives a thiocyanate that reacts with sodium sulfide to give l,2-0-isopropylidene-5-thio-a-D-xylofuranose (212). A better synthesis is the treatment of 211 with sodium thiosulfate, followed by reduction of the resultant Bunte salt with sodium boro-hydride. The same compound 212 is obtained by nucleophilic replacement of the 5-sulfonyloxy group in 211 by treatment with potassium thioacetate followed by deacetylation to 212, or by the reaction of 211 with sodium a-toluenethioxide, followed by scission of the resultant S-benzyl compound with sodium in liquid ammonia. 

Acid hydrolysis of the furanose form 212 results, with spontaneous ring expansion, in the formation of 5-thio-D-xylopyranose (215) as 

At pH 4.4, 5-thio-D-xylopyranose (215) shows a slow mutarotation, namely, [a]p +202 - +178° (half-time, 10 hours). At pH 6.6, however, the half-time is only about 10 minutes. The direction of the rotation shows that 215 crystallizes in the a-D form. The nuclear magnetic resonance spectrum of 215 in deuterium oxide shows the presence of the H-1 proton of both anomers. The diaxial coupling of 8.2 Hz for the H-1 proton at the higher field (t 5.25) corresponds to the )8-D anomer in the CJ(d) conformation of the molecule having a sulfur-containing ring. 

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