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Characterization of the four designer benzodiazepines clonazolam, deschloroetizolam, flubromazolam, and meclonazepam, and identification of their in vitro metabolites


In 2012, the first designer benzodiazepines were offered in Internet shops as an alternative to prescription-only benzodiazepines. Soon after these compounds were scheduled in different countries, new substances such as clonazolam, deschloroetizolam, flubromazolam, and meclonazepam started to emerge. This article presents the characterization of these four designer benzodiazepines using nuclear magnetic resonance spectroscopy, gas chromatography–electron ionization-mass spectrometry, liquid chromatography–tandem mass spectrometry, liquid chromatography–quadrupole time-of-flight-mass spectrometry, and infrared spectroscopy. The major in vitro phase I metabolites of the substances were investigated using human liver microsomes. At least one monohydroxylated metabolite was identified for each compound. Dihydroxylated metabolites were found for deschloroetizolam and flubromazolam. For clonazolam and meclonazepam, signals at mass-to-charge ratios corresponding to the reduction of the nitro group to an amine were observed. Desalkylations, dehalogenations, or carboxylations were not observed for any of the compounds investigated. Furthermore, for clonazolam and meclonazepam, no metabolites formed by a combination of reduction and mono-/dihydroxylation were detected. This knowledge will help to analyze these drugs in biological samples.

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This publication has been produced with the financial support of the Drug Prevention and Information Programme of the European Union (JUST/2011/DPIP/AG/3597), the German Federal Ministry of Health, and the City of Frankfurt/Main.

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Correspondence to Bjoern Moosmann.

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Huppertz, L.M., Bisel, P., Westphal, F. et al. Characterization of the four designer benzodiazepines clonazolam, deschloroetizolam, flubromazolam, and meclonazepam, and identification of their in vitro metabolites. Forensic Toxicol 33, 388–395 (2015).

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  • Designer benzodiazepines
  • Clonazolam
  • Deschloroetizolam
  • Flubromazolam
  • Meclonazepam
  • Phase I metabolism