Probes for narcotic receptor mediated phenomena. 18. Epimeric 6 alpha- and 6 beta-iodo-3,14-dihydroxy-17-(cyclopropylmethyl)-4,5 alpha-epoxymorphinans as potential ligands for opioid receptor single photon emission computed tomography: synthesis, evaluation, and radiochemistry of [125I]-6 beta-iodo-3,14-dihydroxy-17-(cyclopropylmethyl)-4,5 alpha-epoxymorphinan

J Med Chem. 1992 Jul 24;35(15):2826-35. doi: 10.1021/jm00093a016.


The epimeric 6 beta- and 6 alpha-iodo-3,14-dihydroxy-17-(cyclopropylmethyl)-4,5 alpha-epoxymorphinans (1, ioxy) and (2, epioxy), respectively, were each synthesized in five steps starting with naltrexone. The configuration of the 6-iodo group of 1 was unequivocally determined to be beta-based on single crystal X-ray analysis of its precursor 3-acetoxy-6 beta-iodo-14-hydroxy-17-(cyclopropylmethyl)-4,5 alpha-epoxymorphinan (10). Both 1 and 2 as well as their corresponding 3-O-acetates 10 and 11 were found to readily cross the blood-brain barrier and completely reverse the analgesic effects of a 10 mg/kg intraperitoneal dose of morphine sulfate as determined by the paw withdrawal latency test. Compounds 1 and 2 were found to bind with high affinity to mu, delta, and kappa receptors in vitro. In general, 1 and 2 exhibited higher affinity for mu and kappa receptors than naltrexone while the 6 beta-iodo epimer 1 (ioxy) was more potent than its epimer 2. In a comparison of the 6 beta-halogen substituent on binding affinity across opioid receptor subtypes, it was generally found that I greater than Br greater than F. On the basis of the results of in vitro and in vivo testing, 1 was selected as a target for radioiodination and evaluation as a potential single photon emission computed tomography imaging agent for opioid receptors. Carrier-free [125I]-1 was synthesized in near quantitative yield by the sequence of reaction of excess 3-acetoxy-6 alpha-[[(trifluoromethyl)sulfonyl]oxy]-14-hydroxy-17- (cyclopropylmethyl)-4,5 alpha-epoxymorphinan (8) with anhydrous Na125I in dry acetonitrile for 90 min at 76 degrees C followed by deacetylation of the product with 1:1 aqueous ammonia/acetonitrile at 25 degrees C. The potential of [125I]-1 as an in vivo imaging agent for opioid receptors is evaluated and discussed.

MeSH terms

  • Animals
  • Binding Sites
  • Blood-Brain Barrier
  • Brain / diagnostic imaging
  • Brain / metabolism
  • Chromatography, High Pressure Liquid
  • Guinea Pigs
  • Indicators and Reagents
  • Iodine Radioisotopes
  • Male
  • Molecular Structure
  • Morphinans / chemical synthesis
  • Morphinans / metabolism*
  • Morphinans / pharmacology
  • Rats
  • Rats, Inbred Strains
  • Receptors, Opioid / metabolism*
  • Tomography, Emission-Computed, Single-Photon
  • X-Ray Diffraction


  • Indicators and Reagents
  • Iodine Radioisotopes
  • Morphinans
  • Receptors, Opioid
  • 6-iodo-3,14-dihydroxy-17-(cyclopropylmethyl)-4,5-epoxymorphinan