STRUCTURE-SWEETNESS RELATIONSHIPS FOR FRUCTOSE ANALOGS .3. 3-DEOXY DEOXY-D-ERYTHRO-HEXULOSE (3-DEOXY-D-FRUCTOSE) - COMPOSITION IN SOLUTION AND EVALUATION OF SWEETNESS

As part of continuing studies on the structural features responsible f or the intense sweetness of D-fructose, 3-deoxy-D-erythro-hexulose (3- deoxy-D-fructose, 1) was prepared, its solution composition was determ ined, and its taste was evaluated. In aqueous solution, 3-deoxy-D-fruc tose exists as a complex mixture of five tautomeric forms in which the beta-D-pyranose form is preponderant (52.5% at 22 degrees C) and the alpha-D-pyranose form is the least abundant (5%). Quite remarkable is the behavior of the open-chain keto form of 1: its content increases f rom 7.5% at 22 degrees C, to 36% at 82 degrees C, and to 47% at 97 deg rees C, making this form the preponderant one at high temperatures. 3- Deoxy-D-fructose was found to be sweet, albeit probably not as sweet a s D-fructose. The hydroxyl group at C-3 is thus not an essential funct ion of the glycophore of D-fructose. The significance of this result i s discussed in relation to the evidence already available and the dive rgent theories that have been proposed to explain the origin of the sw eet taste of D-fructose.