In Vitro Pharmacological Characterization of a Series of 5‐Cyano Desnitazene Opioids or “Cyanazenes”

ABSTRACT

The new synthetic opioid (NSO) market has been reshaped by the emergence of an opioid class known as “nitazenes,” 2‐benzylbenzimidazole opioids spanning a wide potency range, with several analogues surpassing the potency of fentanyl. The recently identified compound 5‐cyano isotodesnitazene, also referred to as isotocyanazene or isotocyanozene, represents a nitazene analogue with a previously unreported 5‐cyano substitution. This study determined the in vitro μ‐opioid receptor (MOR) activation potential of 5‐cyano isotodesnitazene and related “cyanazene” analogues, in comparison with their desnitazene and 5‐nitro‐substituted counterparts. Using a cell‐based β‐arrestin 2 recruitment assay, 5‐cyano isotodesnitazene (EC ₅₀  = 71.5, E _max  = 117% vs. fentanyl) demonstrated lower potency than its 5‐nitro analogue isotonitazene (EC ₅₀  = 2.55, E _max  = 130%) and fentanyl (EC ₅₀  = 15.1, E _max  = 99.9%) while exhibiting comparable activity to isotodesnitazene (EC ₅₀  = 49.2, E _max  = 113%). Similar in vitro trends were observed for the other three cyanazene analogues examined (5‐cyano protodesnitazene, 5‐cyano etodesnitazene, and 5‐cyano metodesnitazene), indicating that a 5‐cyano substitution does not compensate for the potency loss generally associated with removal of the 5‐nitro group in the nitazene scaffold. Additionally, MOR activation was confirmed in an authentic 5‐cyano isotodesnitazene sample. All cyanazenes and isotodesnitazene were detectable using BTNX nitazene test strips (Version 2.0). The emergence of 5‐cyano isotodesnitazene highlights the continued structural diversification of the nitazene scaffold, underscoring the importance of timely pharmacological characterization, targeted harm reduction strategies, and close monitoring of newly emerging NSO.