Crystal structure of rac-3-[2,3-bis(phenylsulfanyl)-3H-indol-3-yl]propanoic acid

The title compound, C₂₃H₁₉NO₂S₂, was obtained as an unexpected regioisomer from an attempted synthesis of an intermediate for a substituent-effect study on ergot alkaloids. This is the first report of a 1H-indole monothioating at the 2- and 3-positions to give a 3H-indole. In the crystal, the acid H atom is twisted roughly 180° from the typical carboxy conformation and forms centrosymmetric O - H⋯N hydrogen-bonded dimers with the indole N atom of an inversion-related molecule. Together with a weak C - H⋯O hydrogen bond involving the carbonyl O atom, chains are formed along [100].