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Chapter 23: Q51P (page 1255)

The relative configurations of the stereoisomers of tartaric acid were established by the following synthesis:

(1) D-(+)-glyceraldehydediastereomers A and B (separated)

(2) Hydrolysis of A and B using aqueous Ba(OH)2 gave C and D, respectively.

(3) HNO3 oxidation of C and D gave (-)-tartaric acid and meso-tartaric acid, respectively.

(a) You know the absolute configuration of D-(+)-glyceraldehyde, Use Fischer projections to show the absolute configurations of products A, B, C, and D.

(b) Show the absolute configurations of the three stereoisomers of tartaric acid: (+)-tartaric acid, (-)-tartaric acid, and meso-tartaric acid.

Short Answer

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(a) Formation of products A, B, C and D from (+)-glyceraldehyde:

(b)

Step by step solution

01

Explanation of part (a):

D-(+)-glyceraldehyde on treatment with hydrogen cyanide generates diastereomeric pair of which A and B are products.

Cyanide ion acts as a nucleophile and attacks at the planar carbonyl carbon of aldehyde which generates products in which position of hydroxyl group is on either side. Hydrolysis of A and B using barium hydroxide will lead to the formation of C and D products. Cyano group changes to carboxylic group on basic hydrolysis. Further, oxidation with nitric acid is carried out and it will oxidise alcoholic functional group to acid as nitric acid is a strong oxidising agent and you get (-)-tartaric acid and meso-tartaric acid from C and D respectively.


Formation of products A, B, C and D from (+)-glyceraldehyde

02

Explanation of part (b):

Absolute configuration is defined for the chiral molecular entities. Stereochemical descriptions include 鈥淩鈥� and 鈥淪鈥� which stands for Rectus and Sinister respectively. Absolute configuration of a substituent in a molecule is independent of the atoms of groups.

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Most popular questions from this chapter

(a) Figure 23-2 shows that the degradation of D-glucose gives D-arabinose, an aldopentose. Arabinose is most stable in its furanose form. Draw D-arabinofuranose.

(b) Ribose, the C2 epimer of arabinose, is most stable in its furanose form. Draw D-ribofuranose.

Question. Retroviruses like HIV, the pathogen responsible for AIDS, incorporate an RNA template that is copied into DNA during infection. The reverse transcriptaseenzyme that copies RNA into DNA is relatively nonselective and error-prone, leading to a high mutation rate. Its lack of selectivity is exploited by the anti-HIV drug AZT (3鈥�-azido-2鈥�,3鈥�-dideoxythymidine), which becomes phosphorylated and is incorporated by reverse transcriptase into DNA, where it acts as a chain terminator. Mammalian DNA polymerases are more selective, having a low affinity for AZT, so its toxicity is relatively low.

  1. Draw the structures of AZT and natural deoxythymidine.
  2. Draw the structure of AZT 5鈥�-triphosphate, the derivative that inhibits reverse transcriptase.

When the gum of the shrub Sterculia setigera is subjected to acidic hydrolysis, one of the water-soluble components of the hydrolysate is found to be tagatose. The following information is known about tagatose:

(1) Molecular formula C6H12O6

(2) Undergoes mutarotation.

(3) Does not react with bromine water.

(4) Reduces Tollens reagent to give d-galactonic acid and d-talonic acid.

(5) Methylation of tagatose (using excess CH3 I and Ag2O) followed by acidic hydrolysis gives 1,3,4,5-tetra-O-methyltagatose.

(a) Draw a Fischer projection structure for the open-chain form of tagatose.

(b) Draw the most stable conformation of the most stable cyclic hemiacetal form of tagatose.

Question:

a) Draw D-allose, the C3 epimer of glucose.

b) Draw D-talose, the C2 epimer of D-galactose.

c) Draw D-idose, the C3 epimer of D-talose. Now compare your answers with Figure 23-3.

d) Draw the C4 鈥渆pimer鈥� of D-xylose. Notice that this 鈥渆pimer鈥� is actually an L-series sugar, and we have seen its enantiomer. Give the correct name for this L-series sugar.

Does lactose mutarotate? Is it a reducing sugar? Explain. Draw the two anomeric forms of lactose.
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