Carbidopa is a drug that is used in combination with Levodopa and is used to treat Parkinson’s disease and Parkinson’s like symptoms. Carbidopa prevents the breakdown of Levodopa in the bloodstream so more Levodopa can enter the brain.

Carbidopa is a noncompetitive inhibitor of aromatic-L-amino-acid decarboxylase (DOPA Decarboxylase) which is an enzyme used in the biosynthesis of L-tryptophan to serotonin and L-DOPA to dopamine.

Carbidopa is also used in combination with a naturally occurring amino acid, 5-HTP, which is a precursor to the neurotransmitter serotonin and an intermediate in tryptophan metabolism.

Chemical synthesis of Carbidopa involves Strecker reaction and several numbers of impurities and degradants are associated with Carbidopa.
At Pharmaffiliates Analytics and Synthetics P. Ltd. reference standards of the impurities associated with Carbidopa are identified and synthesized, which are listed and classified below:-

• L-Methyldopa - It is the L-isomer of alpha-methyldopa which is a metabolite of Carbidopa

• Carbidopa - impurity C or 3-O-Methyl Carbidopa - an impurity of Carbidopa and used as a potential drug to treat hypertension and Parkinson's disease.

• Carbidopa - impurity D or Cyclohexylidene Carbidopa Methyl Ester - an impurity formed in the commercial synthesis of Carbidopa.

• (S)-Carbidopa Methyl Ester - it is an S-isomer methyl ester prodrug of Carbidopa.

• Ethyl (2S)-3-(3,4-dihydroxyphenyl)-2-hydrazino-2-methylpropanoate- it is an ethyl ester prodrug of Carbidopa.

• (2S)-2-hydrazino-3-(3-hydroxy-4-methoxyphenyl)-2-methylpropanoic acid - an impurity formed in the commercial synthesis of Carbidopa.

• Carbidopa - impurity I or (2S)-3-(3-bromo-4,5-dihydroxyphenyl)-2-hydrazino-2-methylpropanoic acid - an impurity formed in the commercial synthesis of Carbidopa.

• Carbidopa - impurity J or 2-Bromo (S)-Carbidopa - A bromo derivative present as an impurity in Carbidopa.

• Carbidopa - impurity G or 3',4'-Dihydroxyphenylacetone - used in the synthesis of Carbidopa.

• 3-(3,4-dihydroxyphenyl)-2-methylpropanoic acid - It is a metabolite of Carbidopa