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I was faced with a question where the skeletal structure of of D(+)-glucose was given and I was asked to give the right structure of L(-)glucose. I noticed that the correct answer was the one where all the stereocenters had opposite absolute configuration of those of D(+)glucose.

But my question is: Will the dextrorotatory and laevorotatory enantiomers always have a set of stereocenters with opposite absolute configuration?

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Precisely, these are based on the configurations proposed by German chemist Emil Fischer, who established the structures of many sugars.

Emil Fischer elucidated these configurations for the aldohexoses in 1896. According to the Fischer convention, D sugars have the same absolute configuration at the asymmetric center farthest removed from their carbonyl group as does D-glyceraldehyde. The L sugars, in accordance with this convention, are mirror images of their D counterparts,

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Similary,the Fischer projection for glucose is shown below.

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It is very important not to confuse these enantiomers with epimers (two sugars that differ only in the configuration around one carbon atom e.g D-glucose and D-mannose, which differ only in the stereochemistry at C-2)

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References

  • Voet and Voet Biochemistry
  • Lehninnger Principles of Biochemistry
  • Biochemistry (Campbell and Farrel)
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