Identification of a new synthetic cannabinoid in a herbal mixture: 1-butyl-3-(2-methoxybenzoyl)indole

Two unknown cannabimimetic compounds were detected in a seized herbal mixture after gas chromatography–mass spectrometry (GC–MS) screening. To elucidate the chemical structures, 0.3 g of the dried plant material was extracted with methanol and concentrated under reduced pressure. The extract was purified by silica gel column chromatography with methylene chloride and methanol. Pure compounds were isolated by preparative high-performance liquid chromatography (HPLC) and then analyzed by electrospray ionization (ESI) mass spectrometry (MS) with direct flow injection, high-resolution ESI-time-of-flight (TOF)–MS and one-dimensional and two-dimensional nuclear magnetic resonance (NMR) spectroscopy. GC–MS spectra showed that the base ion at m/z 321 for compound 1 was the same as that of 1-pentyl-3-(4-methoxybenzoyl)indole (RCS-4), and the fragment ions were almost the same as those of RCS-4. The GC–MS spectrum of compound 2 was very similar to that of compound 1 except that the mass numbers of the fragment ions at m/z 290, 200, 186, and 173 of compound 2 were equally smaller than those of compound 1 by 14 amu. From these GC–MS results, compound 1 was assumed to be the 2- or 3-methoxy isomer of RCS-4, and compound 2 was assumed to be a 1-butylindole homologue of compound 1. The ESI mass spectra showed a single peak at m/z 322.33 for compound 1 and a single peak at m/z 308.25 for compound 2, which showed the masses of the protonated ions. High-resolution TOF–MS spectra showed the accurate mass numbers of protonated molecular ions at m/z 322.180512 for compound 1 and at m/z 308.164895 for compound 2, suggesting the molecular formulas of C₂₁H₂₃NO₂ and C₂₀H₂₁NO₂, respectively. The ¹H NMR spectra showed signals that suggested 23 and 21 protons for compounds 1 and 2, respectively, while the respective ¹³C NMR spectra showed 21 and 20 carbon signals. All protons and carbons were assigned by their couplings and correlations observed in ¹H–¹H correlation spectroscopy (COSY), ¹H–¹³C heteronuclear multiple bond correlation (HMBC), and ¹H–¹³C heteronuclear single quantum coherence (HSQC) spectra. On the basis of the spectral data, compound 1 was identified as the 2-methoxy isomer of RCS-4; compound 2 was identified for the first time as 1-butyl-3-(2-methoxybenzoyl)indole. Phenazepam and 5-methoxy-N,N-diallyltryptamine (5-MeO-DALT) were also identified as coexisting drugs in the herbal mixture. The contents of compounds 1 and 2 in the mixture were calculated to be 22.4 and 3.45 mg/g, respectively.