Enantioselectivity

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The enantioselectivity is the ratio of the reaction rates of two enantiomers in their conversion. A high enantioselectivity means that one enantiomer is converted much faster than the other.

In an achiral environment and with achiral reaction partners, the reaction rate of enantiomers is the same. On the other hand, the individual enantiomers react differently in a chiral environment or with one enantiomer of a reaction partner.

Medicinal substances

Enantiomers of medicinal substances regularly have different biological and pharmacological effects. In other words: The biological and pharmacological effects of drugs are - apart from special exceptions - enantioselective. The use of enantiomerically pure active ingredients is therefore preferable to the use of racemates. Racemic drugs are sometimes viewed as active ingredients with a purity of 50%.

Flavors and fragrances

Enantiomers of flavorings have a different taste, since the taste receptors are enantioselective because they are themselves chiral and sterically uniform. The amino acid ( R ) -Valin tastes sweet, but ( S ) -Valin tastes bitter.
The same applies to chiral fragrances , such as, for example, carvone . ( S ) -Carvone smells like caraway, ( R ) -Carvone smells like mint, ie the smell is enantioselective.

environment

Drugs are potent environmental chemicals. A phenomenon that is often overlooked by environmental researchers is the peculiarities of the enantioselective degradation of racemic drugs in the environment. For each enantiomer of the drug, the degradation can take place according to a different metabolism. This then results in different toxicological effects of the enantiomers of the drug in the environment. The same applies to chiral racemic pesticides .

Industrial application

The enantioselectivity can be used as a method for obtaining chiral substances in high optical purity. The enantioselectivity of an enzyme with respect to a chiral substrate says something about its ability to convert it selectively and is therefore an important parameter for its use in biocatalysis , e.g. B. the kinetic resolution . The enantioselectivity is expressed by the E-value, which is calculated from kinetic parameters. Since the E-Value is calculated in practice from a logarithmic function, for reasons of accuracy it is not customary to specify E-Values ​​above 200. An E-Value of 1 means a non-selective implementation.

The term enantioselectivity is also used to classify the stereoselectivity of a reaction. In the enantioselective synthesis, high enantioselectivities can be recognized by high ee values .

literature

  • Kurt Faber, Biotransformations in Organic Chemistry , 4th edition, Springer Verlag Heidelberg 2000.
  • Eberhard Breitmaier, Günther Jung, Organic Chemistry , 5th Edition, Thieme Verlag 2005.

Individual evidence

  1. ↑ EJ Ariëns: Stereochemistry, a basis for sophisticated nonsense in pharmacokinetics and clinical pharmacology , European Journal of Clinical Pharmacology 26 ( 1984 ) 663-668, doi : 10.1007 / BF00541922 .
  2. ^ Hermann J. Roth, Christa E. Müller, Gerd Folkers: Stereochemie und Arzneimittel e, Wissenschaftliche Verlagsgesellschaft Stuttgart, 1998, ISBN 3-8047-1485-4 .
  3. ↑ Wolfgang Legrum: Fragrances, between stink and fragrance , Vieweg + Teubner Verlag (2011) p. 35, ISBN 978-3-8348-1245-2 .
  4. ↑ a b Barbara Kasprzyk-Hordern: Pharmacologically active compounds in the environment and their chirality , Chemical Society Reviews 39 ( 2010 ) 4466-4503.