Identification of the Metabolites of 2-oxo-PCPr in Human Urine by UPLC-QTOF MS

2-Phenyl-2-(propylamino)-cyclohexanone (2-oxo-PCPr) is a phencyclidine-type new psychoactive substance (NPS) with dissociative effects. Cases of its abuse have been documented in recent years; however, no data regarding its human metabolism have been reported to date. Understanding the metabolism of 2-oxo-PCPr is essential for detecting its presence in authentic forensic case samples, characterizing the resulting metabolites that may serve as biomarkers in forensic toxicology screening, and elucidating the drug’s pharmacokinetics. Urine is the preferred matrix for metabolite identification in forensic toxicology analysis, as it provides an extended detection window. The present study aimed to identify the metabolites of 2-oxo-PCPr in urine by ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF MS). Authentic urine samples from drug abusers were diluted with acetonitrile, followed by centrifugation. The resulting supernatant was filtered through a 0.22 μm membrane prior to analysis. The metabolites were characterized and structurally elucidated using UPLC-QTOF MS. Accurate masses of precursor and fragment ions, mass errors, and molecular formulas were determined for each metabolite. The results showed that the metabolic biotransformations of 2-oxo-PCPr in urine include hydroxylation, carbonyl reduction, dehydrogenation, dealkylation, combined biotransformations, and glucuronide conjugation. A total of 18 phase I metabolites and 8 phase II metabolites were identified, and potential metabolic pathways were proposed. Among these metabolites, M3, the product of carbonyl reduction, exhibited the strongest chromatographic response and the largest peak area, making it an optimal target metabolite for detecting 2-oxo-PCPr abuse. This study provides a theoretical basis and technical support for the identification of 2-oxo-PCPr-related abuse cases.