AD-1211
AD-1211 is an opioid analgesic drug invented in the 1970s by Dainippon Pharmaceutical Co. It is chemically a 1-substituted-4-prenyl-piperazine derivative, which is structurally unrelated to most other opioid drugs. The ("S")-enantiomers in this series are more active as opioid agonists, but the less active ("R")-enantiomer of this compound, AD-1211, is a mixed agonist–antagonist at opioid receptors with a similar pharmacological profile to pentazocine, and has atypical opioid effects with little development of tolerance or dependence seen after extended administration in animal studies.