Opioid Receptor Modulators with a Cinnamyl Group.

To obtain selective and potent opioid receptor ligands, we synthesized dehydro derivatives of alvimopan and found compound (28f), a selective but modest affinity MOR antagonist weaker than alvimopan (1). We replaced the arylpiperidine unit by an arylpiperazine to obtain the 1-(α-carboxycinnamyl)-4-arylpiperazines like 13h, which to our surprise had no MOR or DOR activity but was a KOR agonist with moderate affinity. In contrast, literature examples of arylpiperazines 4 and 5 were reported to be pan opioid receptor antagonists, while 6 was a MOR agonist.