Amination

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In chemistry, amination is a reaction in which one or more amino groups are introduced into a molecule. Often it is a nucleophilic substitution - e.g. B. a halogen bonded to a carbon atom - is replaced by an amino group (z. B. -NH 2 , -NHR or -NR 2 ). In the simplest case, the amination reagent used is ammonia , but a primary , secondary or tertiary amine can also be used.

In addition, reductive amination , catalytic amination and transamination also count among the amination reactions. The reductive amination can also be carried out enantioselectively . A well-known name reaction is the technically important Leuckart-Wallach reaction , a reductive amination.

The addition of ammonia (NH 3 ) or of primary or secondary amines to C =C double bonds is an amination reaction; The enzyme-catalyzed addition of ammonia to fumaric acid , which leads enantioselectively to ( S ) -aspartic acid , is known. The reaction of ammonia or of primary or secondary amines with oxiranes is also an amination reaction. Aniline can be produced from chlorobenzene with the catalysis of copper dichloride . The reaction is transferable to other aryl halides.

The amination of carboxylic acid esters gives carboxamides .

Biological importance

In the metabolism , ammonia and α-keto acids ( ketocarboxylic acids ) are converted into the corresponding α- amino acids by reductive amination . For example, in the mitochondria, α-ketoglutaric acid is converted to glutamic acid in the presence of ammonia . The toxic effect of ammonia is based, among other things, on this reaction, as it removes α-ketoglutaric acid from the citric acid cycle and thus the mitochondrial respiration, which is linked to the citric acid cycle , comes to a standstill. In addition to reductive amination, transamination is of particular importance in metabolism . This creates α-ketoglutaric acid and ( S ) -alanine from pyruvic acid and ( S ) -glutamic acid .

When proteins are broken down , the peptide bonds are hydrolytically cleaved by endo- and exopeptidases. If the amino acids are to be broken down further, the organism must prevent the release of ammonia (NH 3 ), as this is a strong cell poison . Most amino acids are therefore transaminated first. In this process, for which pyridoxal phosphate (PLP, P5P or PALP) is required as a co-substrate, the amino group is transferred to an α-keto acid (2-oxo acid), with the amino acid becoming an α-keto acid and the previous α-keto acid an amino acid.

See also

Web links

Individual evidence

  1. ↑ a b Christa-Maria Eulitz, Sigrid Scheuermann, Hans-Joachim Thier: Brockhaus ABC Chemie. FA Brockhaus, Leipzig 1965, DNB  450772217 , p. 64 .
  2. ^ Hans Beyer and Wolfgang Walter : Organische Chemie , S. Hirzel Verlag, Stuttgart, 1984, p. 841, ISBN 3-7776-0406-2 .