Abstract

13H-5,14-dihydroquinoxalino[2,3-a]phenothiazine (a new pentacyclic ring system) was synthesized by condensation of diphenylamine and sulphur, which on nitration yielded 1-nitrophenothiazine. Reduction of this compound afforded 1-aminophenothiazine dihydrochloride and subsequent protection of this product with acetic anhydride gave 1-acetylaminophenothiazine. The nitration of this acetylated compound yielded two isomeric compounds: 1-amino-2-nitrophenothiazine and 1-amino-4-nitrophenothiazine. The reduction of the ortho isomer furnished 1,2-diaminophenothiazine which when added to catecol and refluxed with ethanol gave the pentacyclic product 13H-5,14-dihydroquinoxalino[2,3-a]phenothiazine. Structures were established by analytical and spectral data. The results of the neuropharmacological screening data revealed that the novel system possessed neurosedative properties. The ability of this compound to antagonise fortwin – induced climbing behaviour in mice was correlated with neuroleptic potential.

Key words: 13H-5,14-dihydroquinoxalino[2,3-a]phenothiazine, pentacyclic, phenothiazine, neurosedative, fortwin-induced.