Isotonitazene
[CAS# 14188-81-9]

Identification

• Classification: Organic raw materials >> Heterocyclic compound >> Imidazoles
• Name: Isotonitazene
• Synonyms: N,N-diethyl-2-[5-nitro-2-[(4-propan-2-yloxyphenyl)methyl]benzimidazol-1-yl]ethanamine
• Molecular Formula: C₂₃H₃₀N₄O₃
• Molecular Weight: 410.51
• CAS Registry Number: 14188-81-9
• SMILES: CCN(CC)CCN1C2=C(C=C(C=C2)[N+](=O)[O-])N=C1CC3=CC=C(C=C3)OC(C)C

Properties

• Density: 1.2±0.1 g/cm³ Calc.^*
• Boiling point: 584.7±45.0 °C 760 mmHg (Calc.)^*
• Flash point: 307.4±28.7 °C (Calc.)^*
• Index of refraction: 1.587 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Discovery and Applications

Isotonitazene is a synthetic opioid belonging to the benzimidazole class. It is structurally related to etonitazene, which was first synthesized in the 1950s during research on new classes of opioid analgesics. Etonitazene and related benzimidazole derivatives were originally developed by a team of researchers at CIBA in Switzerland, who sought alternatives to morphine with higher potency and different pharmacological properties. Although some compounds in this family demonstrated very strong analgesic activity, they were never introduced into medical practice due to concerns over safety, abuse liability, and respiratory depression.

Isotonitazene emerged decades later as a structural analog of etonitazene, with a different substitution pattern on the benzimidazole core. Unlike the original compounds developed in the mid-20th century, isotonitazene did not appear in pharmaceutical research or therapeutic use but was identified in forensic and toxicological contexts beginning in 2019. It was detected as a novel synthetic opioid in seized drug samples and toxicology cases in Europe and North America. Analytical studies confirmed its identity through nuclear magnetic resonance spectroscopy, mass spectrometry, and comparison with other benzimidazole opioids.

The compound acts as a potent μ-opioid receptor agonist, producing strong analgesic and euphoric effects similar to other opioids but with much higher potency than morphine. Preclinical receptor binding assays have shown that isotonitazene exhibits nanomolar affinity for the μ-opioid receptor, comparable to or greater than fentanyl. Like other opioids, it can cause life-threatening respiratory depression, and its potency significantly increases the risk of overdose in unregulated use.

Isotonitazene has no accepted medical application and is not used in clinical settings. Its appearance has been largely restricted to the illicit drug market, where it has been encountered in counterfeit tablets and powders, sometimes mixed with other opioids or stimulants. Forensic laboratories have reported its involvement in multiple fatal intoxications, underscoring its public health risks. The compound has been classified as a controlled substance in several jurisdictions, including placement in Schedule I under United States federal law in 2020, reflecting its high abuse potential and lack of therapeutic use.

Applications of isotonitazene are limited to forensic and toxicological research. Studies have focused on developing validated analytical methods for its detection in biological fluids and seized materials. Techniques such as liquid chromatography–tandem mass spectrometry (LC-MS/MS) and gas chromatography–mass spectrometry (GC-MS) have been employed to monitor its distribution and metabolism. Understanding its metabolic pathways has been important for interpreting toxicology results, as isotonitazene undergoes extensive biotransformation in the body.

The emergence of isotonitazene highlights the ongoing challenge posed by synthetic opioids designed to circumvent drug control measures. Its structural relation to etonitazene demonstrates how modifications to known opioid scaffolds can yield compounds with high potency but severe risks. Although it represents only one member of the growing class of designer benzimidazole opioids, isotonitazene has become emblematic of the dangers associated with these substances in the context of the global opioid crisis.

References

2023. Validation of an analytical method for quantitation of metonitazene and isotonitazene in plasma, blood, urine, liver and brain and application to authentic postmortem casework in New York City. Journal of Analytical Toxicology, 47(7).
DOI: 10.1093/jat/bkad062
URL: https://pubmed.ncbi.nlm.nih.gov/37638699

2021. Synthesis, Chemical Characterization, and μ-Opioid Receptor Activity Assessment of the Emerging Group of “Nitazene” 2-Benzylbenzimidazole Synthetic Opioids. ACS Chemical Neuroscience, 12(7).
DOI: 10.1021/acschemneuro.1c00064
URL: https://pubmed.ncbi.nlm.nih.gov/33759494

2020. Report on a novel emerging class of highly potent benzimidazole NPS opioids: Chemical and in vitro functional characterization of isotonitazene. Drug Testing and Analysis, 12(2).
DOI: 10.1002/dta.2738
URL: https://pubmed.ncbi.nlm.nih.gov/31743619