A concise approach to the synthesis of all twelve 5-deoxyhexoses: D-tagatose-3-epimerase-a reagent that is both specific and general

2-Deoxy- d -glucitol and 2-deoxy- d -allitol, both prepared as crystalline polyols from d -erythronolactone, are oxidized by Gluconobacter thailandicus NBRC 3254 to 5-deoxy- d - threo -hexulose [5-deoxy- d -fructose = 5-deoxy- l -sorbose] and 5-deoxy- d - erythro -hexulose [5-deoxy- l -psicose = 5-deoxy- d -tagatose], respectively. d -Tagatose-3-epimerase (DTE) equilibrates 5-deoxy- d -fructose to 5-deoxy- d -psicose and 5-deoxy- l -psicose to 5-deoxy- l -fructose, providing substrates for the preparation of all eight d - and l -5-deoxy aldohexoses by aldose isomerases. This combination of chemical and biotechnological methods allows a concise approach to the synthesis of all twelve 5-deoxy hexoses and further demonstrates the range of deoxy sugar substrates on which DTE is active. NMR studies show that 5-deoxy- d -fructose exists solely as the β-pyranose form whereas both pyranoses of 5-deoxy- d -fructose [α:β. 22:78] are observed. [For the sake of clarity, all ketoses in this Letter are shown in blue, alditols in red and aldoses in purple.]