Diastereomers of 5-S-cysteinyldopa.

Diastereomers of 5-S-cysteinyldopa formed from D-dopa and L-cysteine or from L-dopa and D-cysteine can be separated from 5-S-cysteinyldopa formed from L-dopa and L-cysteine by liquid chromatography. The diastereomers have a great potential as internal standards in the analysis of 5-S-cysteinyldopa. They can be used as reference substances in the differentiation of stereospecific enzymatic oxidation of dopa from non-specific oxidation.