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

The title compound, C(23)H(19)NO(2)S(2), 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].