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Tryptophan and Stereoisomerism

Several years ago people who were taking supplements of tryptophan (an essential amino acid that we must take in our food for normal growth and maintenance of a healthy body; without it we could not live) started becoming very ill. Some individuals suggested that tryptophan was what was causing the disease. For most amino acids, the alpha carbon (i.e. the carbon to which a hydrogen, the amino group, and the carboxyl group are bound) is asymmetric, which means that the four groups on this carbon can be arranged in two different manners. This causes amino acids to have two stereoisomers. One stereoisomer is called "d" and the other is called "l." Only "l" amino acids are incorporated into proteins. Suppose the problem with the tryptophan was that it was contaminated with the "d" isomer and this is what caused the problem. How would you go about determining that the tryptophan is contaminated?

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L-tryptophan and D-tryptophan are stereoisomers. In fact, they are "enantiomers" -- chiral compounds that are mirror images of each other. Almost all of their physical and chemical properties are identical. For example, they both have the same melting point and the same boiling point. But such pairs of enantiomers do have two sets of properties that are different:

1. how they interact with other chiral compounds
2. how they interact with plane polarized ...

Solution Summary

This solution discusses the concepts of enantiomers in stereoisomerism to determine whether or not the tryptophan is contaminated. Examples are included for further understanding.