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3-(4-Methoxybenzoyl)-1-pentylindole (RCS-4), a synthetic indole-derived cannabimimetic, was first reported to the European Monitoring Centre for Drugs and Drug Addiction via the Early Warning System by Hungarian authorities in 2010 and later identified in head shop test purchases in Ireland. Using gas chromatography-mass spectrometry, we have identified a series of RCS-4 metabolites in urine samples from individuals admitted to hospitals with symptoms of drug intoxication. The metabolites were tentatively identified as products of (i) aromatic monohydroxylation; (ii) dihydroxylation; (iii) aromatic hydroxylation/oxidation of the N-pentyl chain to a ketone; (iv) O-demethylation; (v) O-demethylation/monohydroxylation of N-pentyl chain; (vi) O-demethylation/oxidation of the N-pentyl chain to a ketone; (vii) O-demethylation/aromatic hydroxylation/oxidation of the N-pentyl chain to a ketone; (viii) N-depentylation/aromatic monohydroxylation; and (ix) N and O-dealkylation. The parent compound was not detected. The O-demethylated metabolites were found to be the most useful metabolic markers for the identification of RCS-4 ingestion.

Studies on the pyrolysis of the synthetic cannabinoid agonist UR-144 ((1-pentyl-1H-indol-3-yl)(2,2,3,3-tetramethylcyclopropyl)methanone) have shown that its major pyrolysis product is a tetramethylcyclopropane ring-opened alkene. Considering that smoking is a common way of ingesting synthetic cannabimimetics, the presence of the metabolites of this pyrolysis product would be expected in biological fluids. Using GC-MS and LC-MS-MS methods, a series of phase I metabolites of UR-144 and its pyrolysis product were detected in the urine samples from patients admitted to hospital with suspected drug intoxication. The metabolites were tentatively identified as the products of mono-hydroxylation, di-hydroxylation, mono-hydroxylation with formation of the carbonyl group on the N-alkyl chain, carboxylation and N-dealkylation with mono-hydroxylation. In the case of the UR-144 pyrolysis product, metabolites with hydration of the aliphatic double bond were also identified. The parent compounds were detected as trace amounts in some urine samples, and the hydrated derivative of the UR-144 pyrolysis product was detected in the majority of samples. The detection of mono-hydroxylated metabolites of UR-144 (LC-MS-MS) and mono-hydroxylated/with hydration metabolites of the UR-144 pyrolysis product (GC-MS) was found to be the most useful method of establishing UR-144 ingestion.

The synthetic cannabinoid, UR-144 ((1-pentyl-1H-indol-3-yl)(2,2,3,3-tetramethylcyclopropyl)methanone), was identified in commercial 'legal high' products (herbal, resin, and powder). Along with this, six related compounds were detected. The most abundant one (2.1) was identified as 4-hydroxy-3,3,4-trimethyl-1-(1-pentyl-1H-indol-3-yl)pentan-1-one, a product of the electrophilic addition of water to the cyclopropane moiety in UR-144. Compound 2.1 was found to be undergo cyclisation which leads to the formation of two additional interconvertable compounds (2.3, tentatively identified as 1-pentyl-3-(4,4,5,5-tetramethyl-4,5-dihydrofuran-2-yl)-1H-indole which is stable only in absence of water and also observed as GC artifact) and 2.2, a protonated derivative of 2.3 which is formed in acidic solutions. The remaining compounds were identified as possible degradation products of the group 2 compounds (4,4,5,5-tetramethyldihydrofuran-2(3H)-one and 1-pentylindoline-2,3-dione) and intermediates or by-products from the synthesis of UR-144 ((1H-indol-3-yl)(2,2,3,3-tetramethylcyclopropyl)methanone, 1-pentyl-1H-indole and 1-(1-pentyl-1H-indol-3-yl)hexan-1-one). Pyrolysis of herbal products containing the group 2 compounds or UR-144 resulted in the formation of 3,3,4-trimethyl-1-(1-pentyl-1H-indol-3-yl)pent-4-en-1-one (3). This was confirmed by separate pyrolysis of 2.1 and UR-144. Also, the two additional minor compounds, 1-(1-pentyl-1H-indol-3-yl)ethanone and 1-(1-pentyl-1H-indol-3-yl)propan-1-one, were detected. Pathways for these transformations are presented.