Imidazolyl-ethylamine

The chemical structure of histamine has similarities to the structures of other biogenic amines, but important differences also exist. Chemically, histamine is 2-(4-imidazolyl)ethylamine (Fig. 14-1). The ethylamine backbone is a common feature of many of the amine transmitters (e.g. dopamine, norepinephrine and serotonin). However, the imidazole nucleus, absent from other known transmitters, endows histamine with several distinct chemical properties. Among these is prototypic tautomerism, a property that permits it to exist in two different chemical forms (Fig. 14-1). The tautomeric properties of histamine are thought to be critical in the... 

Synthesis. Histamine, 2-(4-imidazolyl)ethylamine, is formed by decarboxylation of histidine by the enzyme l.-histidinc decarhoxylase. Most histamine is stored preformed in cytoplasmic granules of mast cells and basophils. 

The standard nomenclature for histamine is 1 //-imidazole4(5)-ethanamine. Nevertheless, (2-aminoethyl)-imidazole and /3-(4-imidazolyl)ethylamine are also used in the biological and theoretical studies. In this paper and in all tautomers/ conformers, the ethylamine group is always in position 5 in the imidazolyl group. 

Histamine consists of -(imidazolyl-4-)ethylamine formed by the decarboxylation of histidine, an essential amino acid (Fig. 1) ... 

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