2,5-Dimethyl-N-Phenyl-3H-diazaphophol-4-imine is a quinonoid tautomer of GABAA and GABAB agonist progabide. According to quantum mechanical calculations, a quinonoid form is predominant in polar solvents, while aromatic tautomer is prevalent in apolar solvents. Progabide is a prodrug of gamma-aminobutyric acid and was investigated for the treatment of epilepsy, Parkinson's disease, schizophrenia, clinical depression, anxiety disorder, and other diseases. Progabide was marketed in France by Sanofi Aventis under tradename Gabrene for use in monotherapy and also as adjunctive therapy for generalized tonic-clonic, myoclonic, partial seizures, and for Lennox‐Gastaut syndrome, in both children and adults.