Questions dealing with carbohydrates

  1. D-Arabinose and D-ribose give the same phenylosazone. D-Ribose can be reduced to give an optically inactive pentitol, ribitol. D-arabinose undergoes the Ruff degradation as follows: The tetrose thus obtained, D-erythrose, undergoes nitric acid oxidation to yield meso-tartaric acid, HO2CCHOHCHOHCO2H. What are the configurations of
    1. D-arabinose?
      2.

    2. D-ribose?

      3.   

        

    3. ribitol?

    4. D-erythrose?

     

  2. Consider the following transformations:

    3. D-erythrose + Br2/H2O ® (+)-"A"

    "A" + HNO3 ® meso-"B" (C4H6O6)

     "B" + D ® "C" (C4H4O5)

    "C" + CH3OH ® "D" (C5H8O6) 

    plus enantiomer

     "D" + BH3 ® "E" (C5H10O5) This selectively reduces the CO2H

     plus enantiomer

     "E" + H3O+ ® racemic "A"

     Hydrolysis of ester gives "A"

  3. The disaccharide amygdalin is found in the pits of many fruits. It is the principal component of the controversial anticancer material, Laetrile. It has been suggested that when ingested in large quantities, amygdalin could have fatal consequences. b -glucosidase, an enzyme in the digestive tract, hydrolyzes b -glucosides. Show what would happen when amygdalin reacts with b -glucosidase and how this could explain the fatal properties of Laetrile.

    4.  Hydrolysis of b link gives cyanohydrin of benzaldehyde which will decompose to give CN-

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Updated August 23, 2002