Question

An important technique for establishing relative configurations among isomeric aldoses and ketoses is to convert both terminal carbon atoms to the same functional group. This can be done either by selective oxidation or reduction. As a specific example, nitric acid oxidation of D-erythrose gives meso- tartaric acid (Section 3.4B). Similar oxidation of D-threose gives \((2 S, 3 S)\)-tartaric acid. Given this information and the fact that D-erythrose and D-threose are diastereomers, draw Fischer projections for D-erythrose and D-threose. Check your answers against Table 25.1.

Short answer

Answer: In D-erythrose, the second carbon atom has the (2S,3S) configuration and the third carbon atom has the (2S,3R) configuration. In D-threose, the second carbon atom has the (2S,3S) configuration and the third carbon atom has the (2S,3S) configuration.

Step-by-step solution

Nitric acid oxidation of both D-erythrose and D-threose creates tartaric acid derivatives, with D-erythrose forming meso-tartaric acid and D-threose forming \((2S,3S)\)-tartaric acid. Tartaric acid has four carbon atoms, the same as D-erythrose and D-threose. Therefore, this reaction should help us determine the relative configurations of these sugars. #Step 2: Draw the product structures#

We need to draw Fischer projections for the given products. \\ Meso-tartaric acid has the following configuration: \\ C1: \((2R,3S)\) \\ C2: \((2S,3S)\) \\ C3: \((2S,3R)\) \\ C4: \((2R,3R)\) \\ \((2S,3S)\)-tartaric acid has the following configuration: \\ C1: \((2R,3S)\) \\ C2: \((2S,3S)\) \\ C3: \((2S,3R)\) \\ C4: \((2R,3R)\) #Step 3: Identify the configuration of D-erythrose and D-threose#

Based on the product structures, we can now identify the configuration of D-erythrose and D-threose. Since both sugars only have four carbons, we can determine their configurations using the meso-tartaric acid and \((2S,3S)\)-tartaric acid configurations. \\ D-erythrose: \\ C1: \((2R,3S)\) \\ C2: \((2S,3S)\) \\ C3: \((2S,3R)\) \\ D-threose: \\ C1: \((2R,3S)\) \\ C2: \((2S,3S)\) \\ C3: \((2S,3S)\) #Step 4: Draw the Fischer projections#

Using the configurations we determined in step 3, we can now draw the Fischer projections for D-erythrose and D-threose. \\ D-erythrose Fischer projection: ``` HO-CHO | D-HO-C-H | L-HO-C-H | D-CH2OH ``` D-threose Fischer projection: ``` HO-CHO | D-HO-C-H | D-HO-C-H | D-CH2OH ```