Structure-metabolism relationships of valine and tert-leucine-derived synthetic cannabinoid receptor agonists: a systematic comparison of the in vitro phase I metabolism using pooled human liver microsomes and high-resolution mass spectrometry
Synthetic cannabinoid receptor agonists, commonly referred to as ‘synthetic cannabinoids’ (SCs), gained popularity as recreational drugs due to their cannabis-like effects. The subclass of valine or tert-leucine-derived SCs has dominated the ‘designer drug’ market in recent years and has been associated with several severe intoxication cases. Most SCs are highly lipophilic compounds and are extensively metabolized prior to renal excretion. Hence, for drug detection in urine samples, the major metabolites of new compounds have to be identified first. The aim of this study was to elucidate structure-metabolism relationships (SMRs) of valine and tert-leucine-derived SCs enabling in-depth understanding of their phase I biotransformation and facilitating the prediction of suitable analytical targets for urine analysis.
After incubation of 32 different valine/tert-leucine-derived SCs with pooled human liver microsomes (pHLM), the phase I metabolite profile of each compound was characterized using liquid chromatography–quadrupole time-of-flight mass spectrometry. By comparing chemical-structural analogs with the relative abundances of their metabolites, SMRs were studied.
The terminal functionality (amide vs. methyl ester), the amino acid side chain (valine vs. tert-leucine), the core ring system (indole vs. indazole), and the N-alkyl side chain (cyclohexyl methyl vs. pentyl vs. 5-fluoropentyl vs. 4-fluorobenzyl) showed distinct differences of metabolic dehalogenation, dehydrogenation, formation of dihydrodiols, hydrolysis, hydroxylation, and N-dealkylation.
The presented pHLM approach proved to be an effective tool for systematic investigation of SMRs. The information gained from this work may be useful for predicting potential SC metabolites for urine analysis.
KeywordsICA INACA Metabolite New psychoactive substance
The authors would like to thank colleagues from different institutions for providing synthetic cannabinoid standards: Dr. Sonja Klemenc (Slovenian National Forensic Laboratory, Ljubljana, Slovenia) and all participants of the ‘RESPONSE’ project providing ADB-CHMICA as well as AMB-CHMICA; Dr. Előd Hidvégi and his group (Hungarian National Institute of Forensic Sciences, Budapest, Hungary) providing MDMB-FUBICA. This study was financially supported by the European Commission [Grants JUST/2011/DPIP/AG/3597 and JUST/2013/ISEC/DRUGS/AG/6421] and the Deutsche Forschungsgemeinschaft [Grant INST 380/92-1 FUGG].
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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