Drugs Affecting The Dopaminergic Systems Of The Brain

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In medical practice, four types of dopaminergic drugs are used, and they can be characterized as dopamine precursors (levodopa), dopamine-releasing drugs (amantadine), dopamine receptor agonists (bromocriptine), and dopamine inactivation inhibitors (selegiline).

Dopamine precursors elevate the concentration of dopamine. Another group, dopamine-releasing drugs, was discovered accidentally while making the antiviral drug amantadine. It can be beneficial to patients who have a depot of dopamine. The third group, dopamine receptor agonists, is a group of adjunct drugs, which allows for treatment with smaller doses than levodopa. Finally, the fourth group of drugs, which is represented by selegiline, are inhibitors of a variety of monoaminooxidases (MAO-B), enzymes that ensure the intercellular inactivation of dopamine in presynaptic nerve endings.

Levodopa: Levodopa, (-)-3-(3,4-dihydroxyphenyl)-l-alanine (10.1.1), is a levorotatory isomer of dioxyphenylalanine used as a precursor of dopamine. There are a few ways of obtaining levodopa using a semisynthetic approach, which consists of the microbiological hydroxylation of l-tyrosine (10.1.1) [1,2], as well as implementing a purely synthetic approach.

Oxidation of l-tyrosine, for selective introduction of a hydroxyl group at C3 of the tyro-sine ring, can be accomplished in a purely synthetic manner by using a mixture of hydrogen peroxide and iron(II) sulfate mixture in water as an oxidant with permanent presence of oxygen [3].

/=\ H2O2 / FeSO4 HO—^ J)—CH2 —CH -COOH -»- HO^ /)—CH2—CH-COOH

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