synthesized novel 15–16 nornaltrexone derivatives 9, 11 and 22 to examine the importance of the cavity in the Beckett–Casy model, which was proposed to interact with the 15–16 ethylene moiety in the morphine structure. All the synthesized compounds showed lower affinities for the opioid receptor than did the naltrexone (10). The binding affinities of 14-OH derivatives 11, in which the rotation of the 9–17