Ohmefentanyl

Ohmefentanyl (β-hydroxy-3-methylfentanyl, OMF, RTI-4614-4) is an extremely potent opioid analgesic drug which selectively binds to the µ-opioid receptor. The Chinese have recorded ohmefentanyl as having a potency that is 6,300 times morphine.

Ohmefentanyl is one of the most potent μ -receptor agonists known, comparable to super-potent opioids such as carfentanil and etorphine which are used for tranquilizing large animals such as elephants in veterinary medicine. In mouse studies, the most active isomer 3R,4S,βS-ohmefentanyl was 28 times more powerful as a painkiller than fentanyl, the chemical from which it is derived, and 6300 times more effective than morphine. Ohmefentanyl has three stereogenic centers and so has eight stereoisomers, which are named F9201–F9208. Researchers are studying the different pharmaceutical properties of these isomers.

The 4"-fluoro analogue (i.e. substituted on the phenethyl ring) of the 3R,4S,βS isomer of ohmefentanyl is one of the most potent opioid agonists yet discovered, possessing an analgesic potency approximately 18,000-fold greater than morphine. Other analogues with potency higher than that of ohmefentanyl itself include the 2'-fluoro derivative (i.e. substituted on the aniline phenyl ring), and derivatives where the N-propionyl group was replaced by N-methoxyacetyl or 2-furamide groups, or a carboethoxy group is added to the 4-position of the piperidine ring. The latter is listed as being up to 30,000 times more potent than morphine.