Analysis of exemestane and 17β-hydroxyexemestane in human urine by gas chromatography/mass spectrometry: development and validation of a method using MO-TMS derivatives.
Trimethylsilylation of anabolic agents and their metabolites is frequently achieved by using the derivatization mixture N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA)/NH(4)I/2-mercaptoethanol. Nevertheless, artifacts were formed when this mixture was employed in the monitoring of exemestane and its main metabolite 17β-hydroxyexemestane prior to GC-MS analysis. These artifacts were identified as the N-methyltrifluoroacetamide (MTFA) and trimethylsiloxyethylmercapto products of the respective trimethylsilyl (TMS) derivatives. Furthermore, artifact formation was evaluated taking the structure (1,4-diene-3-keto-6-exomethylene) of the compounds into account. Although these artifacts are relevant for investigations regarding the derivatization process and may be of interest in many fields, they are detrimental to cope with the requirements of the World Anti-Doping Agency (WADA) in terms of the limits of detection (LODs) required. To overcome this issue, a method using an alternative derivatization was proposed: formation of methyloxime-TMS derivatives through double derivatization using O-methylhydroxylamine/pyridine and MSTFA/TMS imidazole after enzymatic hydrolysis and liquid-liquid extraction. Samples from an excretion study after administration of exemestane to healthy volunteers were analyzed by the proposed method and detection of both exemestane and its main metabolite was possible. This method showed excellent results for both analytes meeting the LODs required for antiestrogenic agents (50  ng/mL) established by WADA. The method was validated for the main metabolite, it was robust and cost-effective for qualitative and quantitative purposes, with LOD and LOQ of 10  ng/mL and 25  ng/mL, respectively.
Universidade Federal do Rio de Janeiro, Instituto de Química, Programa de Pós-graduação em Química, LAB DOP-LADETEC, Ilha do Fundão, Avenida Athos da Silveira Ramos 149, 21941-909 Rio de Janeiro, RJ, Brazil. gcavalcanti83@yahoo.com.br
Gustavo de A
Gde A
Cavalcanti
Bruno C
BC
Garrido
Felipe D
FD
Leal
Monica C
MC
Padilha
Xavier
X
de la Torre
Henrique M G
HM
Pereira
Francisco R
FR
de Aquino Neto
D000081:Acetamides; D000328:Adult; D000730:Androstadienes / Q000737:chemistry / Q000493:pharmacokinetics / Q000652:urine*; D016477:Artifacts; D004300:Doping in Sports; D005463:Fluoroacetates; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D006801:Humans; D008297:Male; D010091:Oximes / Q000737:chemistry; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014269:Trifluoroacetic Acid / Q000737:chemistry; D014297:Trimethylsilyl Compounds / Q000737:chemistry
C555521:17-hydroxyexemestane; D000081:Acetamides; D000730:Androstadienes; D005463:Fluoroacetates; D010091:Oximes; D014297:Trimethylsilyl Compounds; C086665:N-methyl-N-(trimethylsilyl)trifluoroacetamide; D014269:Trifluoroacetic Acid; C056516:exemestane