[Triperidin (Norakin): separation, stability and structure of stereoisomers].

The antiparkinsonian triperiden (1; as hydrochloride Norakin) is a mixture of the stereoisomers 1a and 1b. Their identification and separation by chromatographic methods or fractional crystallisation of the tartrates is described. By means of IR- und 13C-NMR spectral data structures of 1a and 1b are proposed. Under proton catalysis 1b racemizes to 1a. In acidic solution (heating in 0.1 mol.1-1 HCl or storage in gastric juice at 37 degrees C) hydrolysis of 1 takes place and four isomeric products were observed (Z1-Z4), which arise by cleavage of the cyclopropyl moiety. The main product Z2 was identified as the 2"-hydroxy derivative. The solid drug is stable at least for 5 years.