Many chiral molecules are present in nature as single enantiomers
المؤلف:
Jonathan Clayden , Nick Greeves , Stuart Warren
المصدر:
ORGANIC CHEMISTRY
الجزء والصفحة:
ص307-308
2025-05-21
562
Let’s turn to some simple, but chiral, molecules—the natural amino acids. All amino acids have a carbon carrying an amino group, a carboxyl group, a hydrogen atom, and the R group, which varies from amino acid to amino acid. So unless R H (this is the case for glycine), amino acids always contain a chiral centre and lack a plane of symmetry.
It is possible to make amino acids quite straightforwardly in the laboratory. The scheme below shows a synthesis of alanine, for example. It is a version of the Strecker synthesis you met in Chapter 11.
Alanine made in this way must be racemic because the starting material and all reagents are achiral. However, if we isolate alanine from a natural source—by hydrolysing vegetable protein, for example—we fi nd that this is not the case. Natural alanine is solely one enantiomer, the one drawn in the margin. Samples of chiral compounds that contain only one enantiomer are called enantiomerically pure. We know that ‘natural’ alanine contains only this enantiomer from X-ray crystal structures.
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