Analytical Differentiation of 1‑Alkyl-3-acylindoles and 1‑Acyl-3-alkylindoles: Isomeric Synthetic Cannabinoids

Abstract

The 1-alkyl-3-acylindoles and the inverse regioisomeric 1-acyl-3-alkylindoles can be prepared directly from a common set of precursor materials and using similar synthetic strategies. The EI mass spectra for these isomers show a number of unique ions which allow for the differentiation of the 1-alkyl-3-acylindole compounds from the inverse regioisomeric 1-acyl-3-alkylindoles. The base peak at <i>m</i>/<i>z</i> 214 in the 1-<i>n</i>-pentyl-3-benzoylindole represents the M-77 cation fragment resulting from the loss of the phenyl group, and this ion is not observed in the inverse isomer. The 1-benzoyl-3-<i>n</i>-pentylindole inverse regioisomer shows a base peak at <i>m</i>/<i>z</i> 105 for the benzoyl cation. Thus, these two base peaks are the result of fragmentation initiated at the carbonyl-oxygen for both isomers. The 1-pentyl-3-benzoylindole is characterized by the strong intensity carbonyl band at 1703 cm^–1, while the amide carbonyl appears as a strong band of equal intensity at 1681 cm^–1 in the 1-benzoyl-3-pentyl regioisomer