phenylethanolamine

Phenylethanolamine refers to a class of organic compounds characterized by a phenyl group attached to a two-carbon side chain that bears a hydroxyl group on the beta carbon and a primary amine at the terminal carbon. The general structural motif is Ar-CH(OH)-CH2-NH2, where Ar represents a phenyl ring that may be substituted.

When Ar is a 3,4-dihydroxyphenyl ring (a catechol), the molecules are catecholamines, a family of biologically active amines. The most prominent examples are norepinephrine (noradrenaline) and epinephrine (adrenaline), which play key roles as neurotransmitters and hormones in the sympathetic nervous system. Dopamine is related but lacks the beta-hydroxyl group and is not strictly a phenylethanolamine.

Biochemically, phenylethanolamines are derived from tyrosine. In humans, tyrosine is hydroxylated to L-DOPA, decarboxylated to dopamine, which is then hydroxylated by dopamine beta-hydroxylase to norepinephrine; norepinephrine can be methylated by phenylethanolamine N-methyltransferase to form epinephrine. They exert effects by binding to alpha- and beta-adrenergic receptors, regulating heart rate, vascular tone, and metabolic processes.

Clinically, synthetic or naturally derived phenylethanolamines are used as drugs. Epinephrine and norepinephrine are employed as hormones and vasopressors; other derivatives influence treatment of hypotension, cardiac arrest, and anaphylaxis.

See also: catecholamines; tyrosine; adrenergic receptors.