MR-2096 is an opioid analgesic drug related to oxymorphone. It has an unusual chiral tetrahydrofuran-2-ylmethyl substitution on the nitrogen which determines the character of effects, with the (R) enantiomer MR-2096 being an opioid agonist, while the (S) enantiomer MR-2097 has similarly potent opioid antagonist effects. This mix of activities has made these two enantiomers useful for characterising the binding site of the mu opioid receptor.[1]