[Application of difference circular dichroism (CD) spectroscopy for determination of pharmaceutical compounds. Analysis of stereoisomers by the HPLC-CD/UV method].

Circular dichroism (CD) spectroscopy is gaining an increasing importance in pharmaceutical analysis. One of the main advantages of the CD spectroscopic method is its inherent selectivity, which provides the selective analysis of chiral molecules possessing optically active absorbance bands. In addition to direct CD spectroscopic methods, several new procedures have been developed based on CD spectroscopy for the analysis and determination of pharmaceutical compounds in the past few years. One of the most progressive fields of chiroptical analysis is the combination of high performance liquid chromatographic separation and CD spectroscopy and the application of simultaneous dual CD/UV detection. The aim of our research work was to work out new procedures based on CD and CD related techniques and to investigate the application of these methods in pharmaceutical analysis. This work presents a new, selective and sensitive difference CD spectroscopic method based on oxime formation of the keto group for the determination of delta 4-3-ketosteroids and 6-keto-morphinans. Molar CD and UV spectral parameters of E and Z oxime isomers, produced in the course of oxime formation reaction, have been determined by HPLC separation and simultaneous dual CD and UV detection, without isolation of the isomers. The stereochemistry of spirocyclic pyridopyridazine compounds has been investigated by simultaneous dual CD and UV spectroscopy following HPLC separation. The enantiomeric relationship of the pyridopyridazine stereoisomers has been proved by the application of ellipticity-absorbance ratio spectra in a novel way.