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Low level determination of a novel 4-azasteroid and its carboxylic acid metabolite in human plasma and semen using high-performance liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry


Low level determination of a novel 4-azasteroid and its carboxylic acid metabolite in human plasma and semen using high-performance liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry



Journal of Chromatography. B Biomedical Sciences and Applications 693(1): 117-129



ISSN/ISBN: 1387-2273

PMID: 9200525

DOI: 10.1016/s0378-4347(97)00047-9

Compound I (4,7-beta-dimethyl-4-azacholestan-3-one, MK-0386) is a potent 5-alpha-reductase type I (5-alpha-R1) inhibitor. Sensitive (0.2 ng/ml), specific and separate assays have been developed and validated for the analysis of I and its carboxylic acid metabolite (II) in human semen and plasma based on high-performance liquid chromatography (HPLC) with tandem mass spectrometric (MS-MS) detection. After liquid-liquid extraction of the analytes from biological matrix, the extracts were chromatographed on a short (50 mm) analytical column during analysis of I, and on a longer (150 mm) column with a weaker mobile phase during the analysis of II. This additional chromatographic separation was required to separate II from a secondary metabolite present in post-dose plasma samples interfering with the quantification of II. The MS-MS detection was performed on a Sciex API III Plus tandem mass spectrometer using the heated nebulizer probe. Monitoring the parent-+product ion combinations of m/z 416 fwdarw 4114 and 404 fwdarw 114, in the multiple reaction monitoring (MRM) mode, after chromatographic separation, allowed quantification of both analytes. The standard curve in plasma was linear in the concentration range of 0.2 to 200 ng/ml for both I and II, with correlation coefficients greater than 0.99 and coefficients of variation of less than 15% for replicate (n=5) analysis at all concentrations within the standard curve range. For the semen assay the linear range for determination of I was from 0.2 to 50 ng/ml. These assays were applied to support a number of clinical studies with I and their validity and long-term performance was confirmed during analyses of clinical samples from these studies. The need for careful assessment of the specificity of MS-MS assays in post-dose biological fluid samples in the presence of metabolites was emphasized.

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