Separation, conformation in solution and absolute configuration of ethopropazine enantiomers

Enantiomers of ethopropazine x HCl (10-(2-diethylaminopropyl)phenothiazine hydrochloride) were prepared by fractional crystallization of diastereomeric dibenzoyltartaric acid salts, and their optical purity (enantiomeric excess, ee) determined by HPLC on Chiralcel OJ column. With a solvent mixture n-hexane/t-butanol/triethylamine (100:3:0.5) as eluent a very good enantioseparation (alpha = 1.68) for racemic ethopropazine was obtained. Enantiomeric purity for (-)-enantiomer was 99.1% and for (+)-enantiomer 97.9%. Combined data from NMR and CD spectra of both enantiomers, along with previously reported X-ray structure analyses of racemic ethopropazine, revealed skewed conformation of tricyclic system in solution, and (S)-configuration on the stereogenic center for (-)-enantiomer, and (R)-configuration for (+)-enantiomer.