Phenethylamine (β-Phenylethylamine) is an alkaloid and monoamine. In the human brain, it is believed to function as a neuromodulator or neurotransmitter (trace amine). A colorless liquid that forms a solid carbonate salt with carbon dioxide (CO2) upon exposure to air, phenethylamine in nature is synthesized from the amino acid phenylalanine by enzymatic decarboxylation. It is also found in many foods, especially after microbial fermentation, e.g., in chocolate. It has been suggested that phenethylamine from food (e.g., chocolate) may have psychoactive effects in sufficient quantities. However, it is quickly metabolized by the enzyme MAO-B, preventing significant concentrations from reaching the brain.
Substituted phenethylamines are a broad and diverse class of compounds that include neurotransmitters, hormones, stimulants, hallucinogens, entactogens, anorectics, bronchodilators, and antidepressants.
The phenethylamine structure can also be found as part of more complex ring systems such as the ergoline system of LSD or the morphinan system of morphine.
Substituted phenethylamines carry additional chemical modifications at the phenyl ring, the sidechain, or the amino group:
Amphetamines are homologues of phenethylamines carrying an alpha-methyl (α-CH3) group at the sidechain carbon atom next to the amino group.
Catecholamines are phenethylamines carrying two hydroxy groups in positions 3 and 4 of the phenyl ring. Examples are the hormones and neurotransmitters dopamine, epinephrine (adrenaline), and norepinephrine (noradrenaline).
The aromatic amino acids phenylalanine and tyrosine are phenethylamines carrying a carboxyl group (COOH) in alpha position.