The Me analog of fentanyl MeF was first introduced by Paul Janssen J Med Chem    which has been recently revisited by Slavic researchers J Serb Chem    QSAR reveals that the OH was first incorporated into MeF because this pharmacophore had previously been shown to raise the potency of closelyrelated piperidine based narcotics J Med Chem    such as phenoperidine for example AFAIK ohmefentanyl was first reported by Chinese chemists in  Scienta Sinica Vol XXIV No  pp  May  Since that time both Chinese and also American scientists submitted the first elaborate evaluations on OMF isomer variations in  in the JMCJ Med Chem    J Med Chem