6-oxo-morphinane oximes: pharmacology, chemistry and analytical application

The permanent therapeutic importance of morphine derivatives in pain treatment has inspired continual synthetic efforts to modify the rigid pentacyclic systems in search for new selective analgesic agents. As a result, several morphinane oximes have been synthesized recently, which have the additional advantage of possessing an oxime group that can provide a method for selective determination of opiate alkaloids in biological matrices. The oximes of hydrocodone and oxycodone have stronger analgesic effect than the parent ketones and they also proved to be effective in preventing the respiratory depressant and hypotensive actions of fentanyl. In this work a review is given on the present status of oxime pharmacology, chemistry and analysis and also the oxime and O-methyl oxime formation of 6-oxo-morphinanes with therapeutic interest (codeinone, oxycodone, hydrocodone and 14-OH-codeinone). The oxime formation was monitored by reversed-phase HPLC and the chromatographic properties of oxime isomers have been characterized. The assignation of the individual isomers isolated by preparative HPLC was performed by (1)H NMR spectroscopy based on the chemical shift differences of the 5-H signals. In this way the isomeric ratio in the oxime products could also be determined. It was found that in the case of Delta(7)-6-oxo-morphinanes, depending on the substituents, the formation of the Z-isomer highly dominates (73-96%) over that of the E-isomer. However, for the saturated 7,8-(dihydro) derivatives the E-isomer is definitely preferred (>98%). In conclusion of a survey on the theoretical background of oxime isomerism, the conformational differences between the saturated and unsaturated morphinane systems were found responsible for the different E/Z ratios. On the basis of the isomeric ratio and the on-line CD and UV spectra of the pure isomers, the molar ellipticities and absorbancies of the isomers were calculated by a parameter estimation method.