In vitro metabolic profiles of adamantyl positional isomers of synthetic cannabinoids

Abstract

Illegal use of synthetic cannabinoids (SCs) is a serious problem worldwide. Legal regulation of SCs requires fundamental analytical studies regarding the differentiation of potential structural isomers. Accumulation of SC metabolic profiles is also essential for forensic investigation because SCs are immediately metabolized after intake. Thus, we investigated the in vitro metabolism of N-adamantyl-1-(tetrahydropyran-4-ylmethyl)-1H-indazole-3-carboxamide isomers (ATHs) using human liver microsomes (HLMs). Moreover, we validated the applicability of the isomeric differentiation by investigation of N-adamantyl-1-(4-fluorobenzyl)-1H-indazole-3-carboxamide isomers (AFUs). Metabolites were collected at designated time points during the incubation period with HLMs for up to 180 min. The structures of the metabolites were annotated on the basis of mass spectroscopic evidence obtained by liquid chromatography–ion trap–time of flight mass spectrometry. The secondary stage mass (MS2) spectra obtained from the protonated molecules revealed a clear difference in both ATHs and their major metabolites because of the stability of the adamantyl (AD) cation. In HLMs, ATHs were quickly metabolized, and hydroxylation of the AD ring was deduced as the major metabolic pathway. The major metabolites of ATH 1 and ATH 2 after 180 min showed dihydroxylation and monohydroxylation of the AD ring. The AFUs showed analytical and metabolic profiles similar to those of the ATHs described above. We characterized the metabolism of ATHs for the first time and discriminated between the two isomers by mass spectrometric analysis of either the parent compounds or their major metabolites. Our investigation of AFUs also demonstrated a useful method for distinguishing between AD isomers.