Insights into Stereochemistry and Its Relation to Biochemistry

Insights into Stereochemistry and Its Relation to Biochemistry 

It was emphasized above that, during the course of his experimental work, Emil Fischer had to create new concepts on which to base further exploratory research. A few examples of this will now be cited. 

In 1894, Fischer wrote It will probably be possible to obtain all riiem-bers of the sugar group by a combination of the cyanohydrin reaction with the reduction of lactones, as soon as we have succeeded in finding the two optically active forms of glyceraldchyde. All observations agree with the isomerisms foreseen by Van t Hoff, above all the disappearance of isomers if the molecule becomes constitutionally symmetric. This includes the transformation of different stereoisomers into one and the same substance if one of several asymmetric centers is abolished. An example of this is 

In the initial confusion, it was the great achievement of Emil Fischer to disengage himself from Van t Hoff s method of writing configurational formulas, and to go back to the ordered tetrahedral models themselves, for which he had to invent a projection of the steric arrangement onto the plane of depiction. 

Initially, only the nitrile of L-mannonic acid was found on addition of hydrocyanic acid to L-arabinose this acid retained the original arabinose in the asymmetry centers 3, 4, and 5. The new center of asymmetry created in this way at C-2 was first considered by Fischer to be racemic. This would have meant that the L-mannonic acid should be a partial racemate however, attempts to separate it into two stereoisomers failed. The idea of a partial racemate led to the question as to whether L-mannonic acid and D-gluconic acid (which are enantiomorphous on carbon atoms 3, 4, and 5) could form such a partial racemate (which would still be optically active). Such a compound could not be isolated, but negative results have only limited values as proof.  

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VIII. Insights into Stereochemistry and Its Relation to Biochemistry. 34... 

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