Metabolic profile of mephedrone: Identification of nor-mephedrone conjugates with dicarboxylic acids as a new type of xenobiotic phase II metabolites

•Metabolic profile of mephedrone in rat urine was studied.•N-Demethylation and 4-methyl oxidation were the main metabolic pathways.•A set of 13 reference standards was used to support metabolite identification.•A new type of phase II metabolites, conjugates with dicarboxylic acids, was found.

Metabolic profile of mephedrone (4-methylmethcathinone, 4-MMC), a frequently abused recreational drug, was determined in rats in vivo. The urine of rats dosed with a subcutaneous bolus dose of 20 mg 4-MMC/kg was analysed by LC/MS. Ten phase I and five phase II metabolites were identified by comparison of their retention times and MS2 spectra with those of authentic reference standards and/or with the MS2 spectra of previously identified metabolites. The main metabolic pathway was N-demethylation leading to normephedrone (4-methylcathinone, 4-MC) which was further conjugated with succinic, glutaric and adipic acid. Other phase I metabolic pathways included oxidation of the 4-methyl group, carbonyl reduction leading to dihydro-metabolites and ω-oxidation at the position 3′. Five of the metabolites detected, namely, 4-carboxynormephedrone (4-carboxycathinone, 4-CC), 4-carboxydihydronormephedrone (4-carboxynorephedrine, 4-CNE), hydroxytolyldihydro-normephedrone (4-hydroxymethylnorephedrine, 4-OH-MNE) and conjugates of 4-MC with glutaric and adipic acid, have not been reported as yet. The last two conjugates represent a novel, hitherto unexploited, type of phase II metabolites in mammals together with an analogous succinic acid conjugate of 4-MC identified by Pozo et al. (2015). These conjugates might be potentially of great importance in the metabolism of other psychoactive amines.

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