Name:  Levodopa

Synonyms:  3-(3,4-Dihydroxyphenyl)-L-alanine; L-3-(3,4-Dihydroxyphenyl)alanine; L-DOPA

Molecular Structure:  

Molecular Formula:  C₉H₁₁NO₄

Molecular Weight:  197.19

CAS Number:  59-92-7

EINECS:  200-445-2

 

L-DOPA is a drug related compound found in some food and made from L-Tyrosine, which is an amino acid naturally occuring in the human body. L-DOPA is converted into dopamine in the brain and body. Levodopa is sold as a dietary supplement and as a prescription drug in the US. In clinical use, Levodopa (INN) is administered in the management of Parkinson's disease and dopa-responsive dystonia. Levodopa is also used as a component in marine adhesives used by pelagic life. L-DOPA is used to increase dopamine levels for the treatment of Parkinson's disease and dopamine-responsive dystonia, since Levodopa is able to cross the blood-brain barrier, whereas dopamine itself cannot. Once levodopa has entered the central nervous system (CNS), Levodopa is metabolized to dopamine by aromatic L-amino acid decarboxylase. Pyridoxal phosphate (vitamin B6) is a required cofactor for this decarboxylation, and may be administered along with levodopa, usually as pyridoxine.

Conversion to dopamine also occurs in the peripheral tissues, i.e., outside the brain. This may be the mechanism of the adverse effects of levodopa, listed below. It is standard clinical practice to co-administer a peripheral DOPA decarboxylase inhibitor¡ªcarbidopa or benserazide¡ªand often a catechol-O-methyl transferase (COMT) inhibitor, like entacapone, to prevent synthesis of dopamine in peripheral tissue. Co-administration of pyridoxine without a decarboxylase inhibitor accelerates the extracerebral decarboxylation to such an extent that Levodopa cancels out the effects of levodopa administration, a circumstance that historically caused great confusion. For those taking Levodopa as a supplement, EGCG or green tea is a natural decarboxylase inhibitor. Levodopa, co-administered with a peripheral DOPA decarboxylase inhibitor, has been tested as a possible treatment for restless leg syndrome (RLS) and has shown "no clear picture of reduced symptoms".

Both levodopa and its precursor amino acid L-tyrosine are precursors to the biological pigment melanin. The enzyme tyrosinase catalyzes the oxidation of L-dopa to the reactive intermediate dopaquinone, which reacts further, eventually leading to melanin oligomers.