Dithiols. Part XXV. Synthesis of 2,3-dimercaptopropionic acid and 2,3-dimercaptopropanol from cysteine
Deaminative halogenation of L-S-benzylcysteine gives L-3-benzylthio-2-chloropropionic acid, from which 2,3-bis(benzylthio)propionic acid, 2,3-bis(benzylthio)propanol, 2,3-dimercaptopropionic acid, and 2,3-dimercapto-propanol can be prepared. The reaction of the chloro-acid or its methyl ester with potassium thiobenzoate occurs with partial rearrangement (neighbouring group participation) to give mixtures of 2-benzoylthio-3-benzylthio- and 3-benzoylthio-2-benzylthio-compounds, converted by reductive processes into 2,3-dimercaptopropanol. The products are racemic or of low optical purity.