Enantiomers levodopa

Enantioselective synthesis is particularly important in the pharmaceutical industry, because only one enantiomer of a chiral drug is likely to have the desired effect. For example, levodopa [(- )-dopa or Z-dopa] is used in patients with Parkinson s disease to counteract a deficiency of dopamine, one of the neurotransmitters in the brain. Dopamine... 

It should be noted, however, that despite the general preference for the marketing of synthetic chiral therapeutic agents in racemic form, a few synthetic chiral drugs were introduced in a unichiral form. Such exceptions included the above-mentioned levodopa and also n-penicillamine 31 [78], (-)-timolol 32 [87], methyl-dopa 33 [88], etc, and it is clear that in most such cases the choice of developing a unichiral form was dictated by overt serious toxicity present predominantly in the ofher enantiomer. 

The addition of a chiral crown ether [(+)-(18-crown-6)-2,3,ll,12-tetracarboxylic acid] to the background electrolyte allowed Blanco and Valverde [147] to separate the enantiomers of benser-azide and determine the enantiomeric purity of Dopa (3,4-dihydroxyphenyl-alanine). Levodopa is the main active ingredient in the pharmaceutical formulation Madopar , which is used to treat Parkinson s disease, while dextradopa causes unwanted side effects. The dextradopa impurity was clearly resolved from the main peak and determined to be 0.5%. 

An example of a stereospecrfic process is the conversion of the drug levodopa to dopamine, a neuro transmitter in the brain. Levodopa (or L-dopa), the precursor of dopamine, is administered to treat Parkinson s disease. Levodopa has one chiral carbon atom. Therefore, it exists as either of two enantiomers. Only the enantiomer with the configuration shown below is transformed into dopamine. 

The reaction occurs because a stereospecific decarboxylase catalyzes the loss of a carboxyl group by formation of carbon choxide (decarboxylation). This enzyme has a chiral binding site for levodopa, but it does not bind the enantiomer of levodopa. 

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