Herbst-Engel transamination

What is Herbst-Engel transamination?

In 1934, Herbst and Engel first reported a reaction that involves the transfer of an amino group from an α-amino acid to an α-keto acid to form a new α-amino acid. This reaction cannot occur with amino acids that lack an α-hydrogen, such as α-aminoisobutyric acid.

Herbst-Engel transamination - general reaction scheme
Herbst-Engel transamination

The reaction is believed to involve several steps, including the formation of an imino group between an amino and a carbonyl group, hydrogen transfer to the α-carbon of the ketonic acid, elimination of carbon dioxide, and the addition of water resulting in fission and the formation of an aldehyde and a new α-amino acid. The extent of decarboxylation is affected by the substituent on both α-amino acids and α-keto acids, with arylaminoacetic acid exhibiting a faster carbon dioxide evolution rate than aliphatic amino acids. Ortho-substituted arylaminoacetic acid exhibits a faster rate of carbon dioxide evolution than para-substituted, and electron-withdrawing groups accelerate the reaction more than electron-donating groups.

A similar reaction occurs under physiological conditions, catalyzed by enzymes, which is an essential process in amino acid metabolism. However, no decarboxylation occurs for the enzyme-catalyzed reaction. The transamination between α-amino acid and glyoxylate to form glycine and the corresponding keto acid completes in about 10 minutes when catalyzed by copper or iron salts.

References

Herbst, R. M., and Engel, L. L. (1934). A reaction between α-ketonic acids and α-amino acids. Journal of Biological Chemistry, 107(2), 505-512
DOI: 10.1016/S0021-9258(18)75369-6

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