Metabolism and toxicological detection of a new designer drug, N-(1-phenylcyclohexyl)propanamine, in rat urine using gas chromatography–mass spectrometry

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Abstract

Studies are described on the metabolism and the toxicological detection of the phencyclidine-derived designer drug N-(1-phenylcyclohexyl)-propanamine (PCPR) in rat urine using gas chromatographic–mass spectrometric techniques. The identified metabolites indicated that PCPR was metabolized by hydroxylation of the cyclohexyl ring at different positions, hydroxylation of the phenyl ring, N-dealkylation, and combinations of these steps. Parts of the metabolites were excreted in conjugated form. The authors’ systematic toxicological analysis (STA) procedure using full-scan GC–MS after acid hydrolysis, liquid–liquid extraction and microwave-assisted acetylation allowed the detection of an intake of a common drug users’ dose of PCPR in rat urine. Assuming similar metabolism in humans, the STA should be suitable for proof of an intake of PCPR in human urine.

Introduction

In the late 1990s, a considerable number of new synthetic drugs from various (new) drug classes were seized in the German federal state of Hesse and surrounding federal states. One of these substances was N-(1-phenylcyclohexyl)-propanamine (PCPR, structure depicted next to mass spectrum no. 1 in Fig. 1), a phencyclidine-derived compound. After a short time, further members of this new class of phencyclidine-derived designer drugs appeared on the illicit drug market, namely N-(1-phenylcyclohexyl)-3-methoxy-propanamine (PCMPA), N-(1-phenylcyclohexyl)-2-methoxy-ethanamine (PCMEA) and N-(1-phenylcyclohexyl)-2-ethoxyethanamine (PCEEA). The seized preparations contained either one compound alone or in mixture with other designer drugs [1]. No information is available on pharmacological properties of these compounds. However, due to structural similarities the pharmacological properties might be assumed to be similar to those of phencyclidine or ketamine, which both act as antagonists at N-methyl-d-aspartate (NMDA) receptors and have psychotomimetic as well as anesthetic properties [2]. Furthermore, it has been reported that (1-phenylcyclohexyl)-amine, a common metabolite of phencyclidine and metabolite of the above-mentioned phencyclidine-derived compounds, produced a long-lasting dose-dependent effect on the efflux of dopamine in rat [3]. Certainly, such pharmacological profiles would be in line with abuse of the new phencyclidine-derived compounds as designer drugs. Anticonvulsant activity of (1-phenylcyclohexyl)-amine and some derivatives were reported by Thurkauf et al. [4].

So far, studies on the metabolism and the toxicological detection have only been described for N-(1-phenylcyclohexyl)-3-ethoxypropanamine (PCEPA) [5]. Such studies are necessary for developing toxicological screening procedures in urine, especially if the drugs are excreted primarily or even exclusively in form of metabolites and for toxicological risk assessment, because the metabolites may play a major role in drug toxicity. Therefore, the aim of this study was to identify the metabolic pathways of PCPR using gas chromatography–mass spectrometry (GC–MS) with electron ionization (EI) and positive-ion chemical ionization (PICI) mode. In addition, the detectability of PCPR and its metabolites within the authors’ systematic toxicological analysis (STA) procedure in urine by GC–MS [5], [6], [7], [8], [9], [10] was studied.

Section snippets

Chemicals and reagents

PCPR HCl was provided by the Hessisches Landeskriminalamt (Wiesbaden, Germany). N-Methyl-bis-trifluoroacetamide (MBTFA) was obtained from Fluka (Taufkirchen, Germany). Isolute Confirm HCX cartridges were obtained from Separtis (Grenzach-Wyhlen, Germany). All other chemicals and biochemicals were obtained from Merck (Darmstadt, Germany). All chemicals and biochemicals were of analytical grade.

Urine samples

The investigations were performed using urine of male Wistar rats (Ch. River, Sulzfleck, Germany) for

Identification of the metabolites

The urinary metabolites of PCPR were separated by GC and identified by EI MS and PICI MS after gentle enzymatic hydrolysis, extraction, and derivatization. GC–MS was preferred to LC–MS due to the better separation power and the better structural information given by EI fragmentation in contrast to electrospray ionization. This was particularly relevant in this study because several isomers had to be differentiated. Finally, GC–MS is still the most often used technique for urine screening.

Gentle

Conclusions

The metabolism studies presented here showed that the designer drug PCPR was mainly metabolized by hydroxylation of the cyclohexyl ring in different positions, hydroxylation of the phenyl ring, N-dealkylation, and combinations of these steps. As other studies have shown [6], [19], [33], [34], [35], it can be assumed that the metabolites found in rat urine should also be present in human urine. Therefore, it can be concluded that the procedure should also be applicable for human urine screening

Acknowledgements

The authors like to thank Denis S. Theobald, Jochen Beyer, Andreas H. Ewald, Gabriele Ulrich, and Armin A. Weber for their support.

References (35)

  • H. Takeda et al.

    Neuropharmacology

    (1986)
  • A.H. Ewald et al.

    J. Chromatogr. B

    (2005)
  • F.T. Peters et al.

    J. Chromatogr. B

    (2005)
  • D. Springer et al.

    J. Chromatogr. B

    (2003)
  • D. Springer et al.

    J. Chromatogr. B

    (2003)
  • D. Springer et al.

    J. Chromatogr. B

    (2003)
  • D. Springer et al.

    J. Chromatogr. B

    (2003)
  • D. Springer et al.

    J. Chromatogr. B

    (2002)
  • R.F. Staack et al.

    J. Chromatogr. B

    (2002)
  • R.F. Staack et al.

    J. Chromatogr. B

    (2004)
  • L.D. Paul et al.

    J. Chromatogr. B

    (2003)
  • R.F. Staack et al.

    J. Chromatogr. B

    (2003)
  • M. Balikova

    Forensic Sci. Int.

    (2005)
  • P. Roesner et al.

    Toxichem. Krimtech.

    (1999)
  • H.P. Rang et al.

    Pharmacology

    (1999)
  • A. Thurkauf et al.

    J. Med. Chem.

    (1990)
  • C. Sauer et al.

    J. Mass Spectrom.

    (2006)
  • Cited by (0)

    Parts of these results were presented at the 16th Microsomes and Drug Oxidation (MDO) Symposium, 3–7 September 2006, Budapest, Hungary.

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