<unk> , also known as levodopa and -3,4-dihydroxyphenylalanine, is an amino acid that is made and used as part of the normal biology of some plants and animals, including humans. Humans, as well as a portion of the other animals that utilize<unk> , make it via biosynthesis from the amino acid -tyrosine.<unk>  is the precursor to the neurotransmitters dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline), which are collectively known as catecholamines. Furthermore,<unk>  itself mediates neurotrophic factor release by the brain and CNS.<unk>  can be manufactured and in its pure form is sold as a psychoactive drug with the INN levodopa; trade names include Sinemet, Pharmacopa, Atamet, and Stalevo. As a drug, it is used in the clinical treatment of Parkinson's disease and dopamine-responsive dystonia.<unk>  has a counterpart with opposite chirality,<unk> . As is true for many molecules, the human body produces only one of these isomers (the<unk>  form). The enantiomeric purity of<unk>  may be analyzed by determination of the optical rotation or by chiral thin-layer chromatography (chiral TLC).
L-DOPA
D-DOPA
4-Methylaminorex
Phenserine
Fluorodopa
Nicotinamide
Glutamate 
Tuaminoheptane