title: Mass spectrometric characterization of efaproxiral (RSR13) and its implementation into doping controls using liquid chromatography-atmospheric pressure ionization-tandem mass spectrometry.
abstract: Efaproxiral (2-[4-[[(3,5-dimethylanilino)carbonyl]methyl]phenoxyl]-2-methylpropionic acid, formerly referred to as RSR13) is prohibited in sports according to the World Anti-Doping Agency (WADA). The drug as well as structurally related compounds and a stable isotope-labeled derivative have been synthesized to elucidate the fragmentation pathway of efaproxiral, using electrospray ionization (ESI) and tandem mass spectrometry by employing a novel linear ion trap--orbitrap hybrid mass spectrometer--in positive and negative ionization modes. The elimination of 2-methyl acrylic acid (-86 u) has been identified as a major fragmentation process in both charge states. Negative ionization and collision-induced dissociation (CID) caused an additional release of carbon dioxide (-44 u), and positive ionization the loss of formic acid (-46 u). Efaproxiral was incorporated into an existing screening procedure for doping controls using solid-phase extraction (SPE) followed by liquid chromatography-tandem mass spectrometry, enabling a limit of detection of 2.5 ng/ml and interday precisions ranging from 7.9 to 13.0%.
authors.affiliation: Institute of Biochemistry and the Competence Center for Preventive Anti-Doping Research, German Sport University Cologne, Carl-Diem Weg 6, 50933 Cologne, Germany. m.thevis@biochem.dshs-koeln.de
authors.forename: Mario
authors.initials: M
authors.lastname: Thevis
authors.forename: Oliver
authors.initials: O
authors.lastname: Krug
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Schänzer
mesh_terms: D000814:Aniline Compounds / Q000737:chemistry / Q000493:pharmacokinetics / Q000652:urine*; D000986:Antisickling Agents / Q000737:chemistry / Q000493:pharmacokinetics / Q000652:urine*; D002853:Chromatography, Liquid / Q000379:methods* / Q000592:standards; D004300:Doping in Sports; D006801:Humans; D011422:Propionates / Q000737:chemistry / Q000493:pharmacokinetics / Q000652:urine*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods* / Q000592:standards
chemical_list: D000814:Aniline Compounds; D000986:Antisickling Agents; D011422:Propionates; C067396:efaproxiral