Metabolism of the Synthetic Cathinone Alpha-Pyrrolidinoisohexanophenone in Humans Using UHPLC--MS-QToF

Alpha-pyrrolidinoisohexanophenone (α-PHiP/α-PiHP) is a synthetic drug structurally related to cathine, a natural psychoactive alkaloid, isolated from Khat plant. The α-PiHP is a structural isomer of α-PHP, and both α-PHP and α-PiHP could be considered an analog of α-PVP, a Schedule I drug under the Convention on Psychotropic Substances by the United Nations. This α-pyrrolidinophenone was first reported to European Monitoring of Drug and Drug Addiction by Slovenia in December 2016. In Hungary, it was initially reported in August 2016, and until 2021, it had been detected in seizures only twice and never been identified in biological samples. However, in 2021, its consumption became prevalent in Hungary. This study aims to investigate the α-PiHP metabolites by performing in vitro and in vivo metabolite identification studies of human liver microsome (pHLM), S9 fraction (pS9) and urine samples (from control and users), using liquid chromatography in conjunction with high-resolution mass spectrometry. Ten in vivo urinary metabolites of α-PiHP were tentatively identified and confirmed by in vitro metabolites detected in pHLM and pS9 samples. Among the eight Phase I and the two Phase II metabolites, five were more abundant in urine than the parent compound. The two major metabolites via reduction of the keto moiety (M01) and via oxidation of the pyrrolidine ring combined with aliphatic hydroxylation and keto reduction (M06) were identified. The metabolites via the combination of keto reduction and aliphatic hydroxylation (M04), via ring-opening followed by carboxylation (M09) and via glucuronidation of the keto reduced metabolite (M07) were also dominant. The minor metabolites were one Phase II metabolite (M08), two metabolites via aliphatic hydroxylation (M02 and M03), one metabolite via the combination of keto reduction and oxidation of the pyrrolidine ring (M05) and one metabolite via oxidation of the pyrrolidine ring (M10).