Classics in Chemical Neuroscience: U-47700.

U-47700, 3,4-dichloro--((1,2)-2-(dimethylamino)cyclohexyl)--methyl benzamide, is a novel synthetic opioid (NSO), discovered by the Upjohn company in the late 1970s. With potent activity, ∼10-times greater than that of morphine, U-47700 has become a drug of widespread abuse due to its ease of synthesis and, until recently, lack of robust detection methods by law enforcement. U-47700 has been found in counterfeit oxycodone tablets and is a key ingredient in "gray death." Due to its emergence worldwide in the past 5 years, it is now a Schedule I drug in the United States and similarly designated around the world; moreover, at autopsy, U-47700 was found to have contributed to the death of the pop artist Prince. This Review will capture the >40 year history of U-47700 and go in-depth regarding the synthesis, medicinal chemistry, / pharmacology, drug metabolism (from postmortem overdose cases), and societal impact of this Classic in chemical neuroscience.