Letter: Enhancement of optical rotation of levodopa by cyclization.

@article{Chafetz1974LetterEO,
  title={Letter: Enhancement of optical rotation of levodopa by cyclization.},
  author={Lester Chafetz and T. M. Chen},
  journal={Journal of pharmaceutical sciences},
  year={1974},
  volume={63 5},
  pages={
          807-8
        }
}
Abstract The optical rotation of levodopa is an important purity criterion, since it provides the only means to control the presence of the allegedly toxic and therapeutically inactive D-isomer. The specific rotation, [α]D 25 , of levodopa is only about − 12°, which is insufficient to control optical purity. Barooshian et al. (1) proposed a TLC limit test for d-dopa in levodopa, involving conversion of the enantiomers to diastereomeric dipeptides. Jouin and Saias (2) and Coppi et al. (3… 
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References

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Quantitative determination of D-dopa present in levodopa samples.
TLDR
A method based on the ability of an L-amino acid decarboxylase, present in a Streptococcus faecalis suspension, to convert quantitatively L-dopa to dopamine while D-dop remains unchanged is reported.
[Enhancement of optical rotatory power of L-DOPA].