Syntheses have been described of the 2-acetamido-2-deoxy derivatives of 5-thio-Dglucose [1-3], 5-thio-I>mannose [4], and 5-thio-D-allose [5]. We now describe the synthesis of another member of this series, 2-acetamido-2-deoxy-5-thio-I)-altrose.
Treatment of oxirane 1 [6] with sodium azide and ammonium chloride in hot aqueous ethanol gave a mixture (70:30) of the altro and gluco azides, 2 and 3, respectively. These were separated by chromatography and identified by their 1H NMR spectra (see Table 1). Thus, the altro azide 2 showed only a single diaxial coupling (J4,5 10.6 Hz) while the gluco isomer 3 displayed three such couplings (J2 3 9.7, J3 4 9.0, and J4,5 10.2 Hz), both compounds being constrained into the C 1 conformation by the acetal protecting group. Both 2 and 3 were further characterised as their acetates 4 and 5. Removal of the acetal protecting group from 2 and 3 by mild acid hydrolysis afforded the azidoglycosides 6 and 8. These were also further characterised as their triacetates 7 and 9, and although it could not be crystallised, the gluco isomer 9 was shown to be identical in all other respects (NMR, [a] D) to that obtained earlier [7] by a different route. Sodium borohydride [8] readily reduced the altro azide 2 to the corresponding amine 10 in conditions which left the gluco isomer 3 unchanged. Indeed, it was more convenient to reduce the mixture of 2 and 3 and then separate 10 from unchanged 3 than it was to separate the mixture of 2 and 3 and then to reduce 2. A shorter route to 10 was to treat the oxirane 1 directly with methanolic ammonia in a sealed tube. Although TLC