The E-isomer of 7-benzylidenenaltrexone (BNTX, 1a) was reported by Portoghese as a highly selective δ-opioid antagonist. The corresponding Z- isomer 1b was not readily available through direct aldol condensation of naltrexone (6) with benzaldehyde. Using the photochemical methods employed by Lewis to isomerize cinnamamides, we have obtained Z-isomer 1b in good yield from E-isomer 1a. A series of (E)- and (Z)-7-arylidenenaltrexone derivatives was prepared to study the effect of larger arylidene groups on opioid receptor affinity in this series. By aldol condensation of naltrexone (6) with benzaldehyde, 1-naphthaldehyde, 2-naphthaldehyde, 4-phenylbenzaldehyde, and 9-anthracaldehyde, the (E)-arylidenes were readily obtained. Photochemical isomerization afforded the corresponding Z-isomers. These compounds were evaluated via opioid receptor radioligand displacement assays. In these assays, the Z-isomers generally had higher affinity and were more D- selective than the corresponding E-isomers. The (Z)-7-(1- naphthylidene)naltrexone (3b) showed the greatest selectivity (δ:μ ratio of 15) and highest affinity δ-binding (K(i) = 0.7 nM). PM3 semiempirical geometry optimizations suggest a significant role for the orientation of the arylidene substituent in the binding affinity and δ-receptor selectivity. This work demonstrates that larger groups may be incorporated into the arylidene portion of the molecule with opioid receptor affinity being retained.
CITATION STYLE
Palmer, R. B., Upthagrove, A. L., & Nelson, W. L. (1997). (E)- and (Z)-7-arylidenenaltrexones: Synthesis and opioid receptor radioligand displacement assays. Journal of Medicinal Chemistry, 40(5), 749–753. https://doi.org/10.1021/jm960573f
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