Sign Up for a Free Account

This is an image preview.
Start a Free Account
to view the full image.

  • Nearly 3,000 illustrations, including video clips of neurologic disorders.

  • Every article is reviewed by our esteemed Editorial Board for accuracy and currency.

  • Full spectrum of neurology in 1,200 comprehensive articles.

  • Listen to MedLink on the go with Audio versions of each article.

Comparison of prodrugs L-DOPA and L-DOPS (droxidopa)

The top row shows the conversion of the prodrug L-DOPA (3,4-dihydroxy-L-phenylalanine, levodopa) to dopamine by aromatic L-amino acid decarboxylase (dopa-decarboxylase). The bottom row shows the conversion of L-DOPS (dl-dihydroxyphenylserine, droxidopa) to norepinephrine by the same enzyme. Both are simple decarboxylation reactions at the same part of the molecules. The only difference between L-DOPA (top left) and L-DOPS (bottom left) is that L-DOPS is hydroxylated at the carbon adjacent to the aromatic catechol moiety. The catecholamines dopamine (upper right) and norepinephrine (bottom right) differ by this same hydroxyl group. Under normal circumstances, dopamine can be concerted to norepinephrine by the enzyme dopamine beta-hydroxylase. This is not possible, however, in patients with dopamine beta-hydroxylase deficiency. Administering the synthetic prodrug L-DOPS (droxidopa) allows that blocked step to be bypassed, so that norepinephrine can be synthesized in vivo by decarboxylation. (Image by Dr. Douglas Lanska 2016.)

Related Media

Associated Disorders

  • Atrial fibrillation
  • Orthostatic hypotension
  • Syncope