A dealkylation reaction of tertiary amines using chloroformate was a useful method for synthesizing morphinan derivatives without 17-substituents; however, the reaction has been applied to only the 14-hydromorphinans. In the course of the investigation of the 17-dealkylation reaction in 14-hydroxymorphinan, the novel cleavage reaction of the C16–N17 bond in the naltrexone derivative was found. A plausible
D-ring would have the loneelectronpair directing in pseudo-equatorial position. These results strongly supported the proposal that the axial orientation of the loneelectronpair on nitrogen would provide sufficient binding abilities to the opioid receptor and that the 15–16 ethylene moiety in the morphine structure would play a role in fixation of the loneelectronpair in the axial direction rather
Treatment of oxazolidinone carboxylic acid 6 with potassium carbonate gave olefin 7 by a double decarboxylation reaction. The reaction was proposed to proceed via decarboxylation followed by E1cB-like mechanism. 15,16-Nornaltrexone derivative 17 prepared from double decarboxylation product 7 showed strong affinity for the μ opioid receptor, indicating it to be a new opioid lead compound.
17-seco-naltrexone derivatives 3 were synthesized using a 16–17 bond cleavage reaction of naltrexone as the key reaction to examine the Beckett–Casy model. All the prepared 16,17-seco-naltrexone derivatives 3 showed lower affinities for opioid receptors than naltrexone. Although the results of binding assay seem to support the existence of a cavity in the model, further investigation using 15,16-nornaltrexone