ESTIMATION OF IMPURITY PROFILES OF DRUGS AND RELATED MATERIALS .12. ISOLATION AND IDENTIFICATION OF AN ISOMERIC IMPURITY IN DANAZOL

We report on a new isomeric impurity of danazol. This impurity designa ted as isodanazol was detected by reversed-phase highperformance liqui d chromatography (HPLC) and thin-layer chromatography (TLC). Its struc ture was determined after separation by preparative HPLC. Mass spectro metry revealed the isomeric nature of the impurity while the UV spectr um indicated profound difference in the isoxazole moieties. The struct ure of the isomeric isoxazole ring in isodanazol was determined by NMR spectroscopy using COSY, HETCOR and NOE measurements. The difference between the UV spectra of danazol and isodanazol is explained on the b asis of the difference between the aromaticities of their isoxazole ri ngs supported by quantum chemical calculations. The quantitative deter mination of the impurity down to the 0.05% level can be performed by H PLC, gas chromatography and TLC densitometry.