5-thio- D-ribopyranose : Part I. The free sugar and the methyl glycosides

Abstract

5-Thio- D-ribose has been synthesised from methyl 2,3-isopropylidene-5- O-toluene- p-sulphonyl-β- D-ribofuranoside. Two crystalline forms of the sugar having different signs of optical rotation were obtained although, more commonly, they co-crystallised. The absence of an SH absorption in their infrared spectra indicates the dextrorotatory and laevorotatory forms to be the α- D-pyranose and β- D-pyranose isomers, respectively. Their mutarotation curves are simple, in contrast to that of β- D-ribopyranose, suggesting the absence of furanoid forms in the equilibria. Methyl 5-thio-α- and β- D-ribopyranosides are the major products of the Fischer reaction of the sugar with methanolic hydrogen chloride. The two thiopyranosides undergo acidic hydrolysis more readily than the corresponding methyl α- and β- D-ribopyranosides.