Several 2-benzylbenzimidazole opioids (also referred to as ‘nitazenes’)
recently emerged on the illicit market. The most frequently encountered
member, isotonitazene, has been identified in multiple fatalities since
its appearance in 2019. Although recent scheduling efforts targeted
isotonitazene, many other analogues remain unregulated. Being
structurally unrelated to fentanyl, little is known about the harm
potential of these compounds. In this study, ten nitazenes and four
metabolites were synthesized, analytically characterized via four
different techniques, and pharmacologically evaluated using two
cell-based β-arrestin2/mini-Gi recruitment assays monitoring µ-opioid
receptor (MOR) activation. Based on absorption spectra and retention
times, high-performance liquid chromatography coupled to diode-array
detection (HPLC-DAD) allowed differentiation between most analogues.
Time-of-flight mass spectrometry (LC-QTOF-MS) identified a fragment with
m/z 100.11 for 12/14 compounds, which could serve as a basis for
MS-based nitazene screening. MOR activity determination confirmed that
nitazenes are generally highly active, with potencies and efficacies of
several analogues exceeding that of fentanyl. Particularly relevant is
the unexpected very high potency of the N-desethyl-isotonitazene
metabolite, rivalling the potency of etonitazene and exceeding that of
isotonitazene itself. Supported by its identification in fatalities,
this likely has in vivo consequences. These results improve our
understanding of this emerging group of opioids by laying out an
analytical framework for their detection, as well as providing important
new insights into their MOR activation potential.
Synthesis, Chemical Characterization, and μ-Opioid Receptor Activity Assessment of the Emerging Group of “Nitazene” 2-Benzylbenzimidazole Synthetic Opioids