Structure elucidation and identification of a common metabolite for naphthoylindole-based synthetic cannabinoids using LC-TOF and comparison to a synthetic reference standard

Abstract

The identification of a predominate metabolite found in urine specimens which test positive for naphthoylindole-based synthetic cannabinoids is reported. The presence of this new metabolite was detected at the Air Force Drug Testing Lab Investigations Division during screening analysis for metabolites of JWH-018 and JWH-073, because it shares the same MRM transitions as the JWH-073 N-(3-hydroxybutyl) metabolite. However, the detected peak is chromatographically distinguished from other metabolites due to differences in retention time. This metabolite appears to be a common metabolite for select naphthoylindole-based synthetic cannabinoids that could potentially be used as a common biomarker for their qualitative and quantitative analyses. The new metabolite has been successfully identified as 3-(3-(1-naphthoyl)-1H-indol-1-yl) propanoic acid (1, JWH 072 N-propanoic acid metabolite, Fig. 1) by using various mass spectrometric and liquid chromatographic techniques as well as chemical derivatization. The metabolite identity was confirmed through the comparison of authentic positive urine and a chemically synthesized metabolite standard. Both materials shared the same chromatographic retention time on two separate chromatographic systems, mass fragmentation pattern and exact mass. Full characterization of the synthetic reference material and intermediates by 1H NMR, 13C NMR, IR and HRMS was also conducted.