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An efficient synthesis of 3-OBn-6β,14-epoxy-bridged opiates from naltrexone and identification of a related dual MOR inverse agonist/KOR agonist

University of New England, College of Arts and Sciences, Chemistry & Physics Department, Biddeford, ME 04005, USA
Bioorganic & medicinal chemistry letters (Impact Factor: 2.33). 06/2012; 22(22):6801-5. DOI: 10.1016/j.bmcl.2012.06.056
Source: PubMed

ABSTRACT In an effort to better understand the conformational preferences that inform the biological activity of naltrexone and related naltrexol derivatives, a new synthesis of the restricted analog 3-OBn-6β,14-epoxymorphinan 4 is described. 4 was synthesized starting from naltrexone in 50% overall yield, proceeding through the OBn-6α-triflate intermediate 8. Key steps to the synthesis include benzylation (96% yield), reduction (90% yield, α:β:3:2), followed by a one-pot triflation/displacement sequence (96% yield) to yield the desired bridged epoxy derivative 4. X-ray crystallographic analysis of intermediate 3-OBn-6α-naltrexol 7a supports population of the key boat conformation required for the epoxy ring closure. We also report that the 6β-mesylate 10-a high affinity opioid receptor ligand, the epimeric derivative of 11, and an analog of 12-functions as an inverse agonist at the mu opioid receptor using herkinorin pre-conditioned cells and an agonist at the kappa opioid receptor when evaluated in independent in vitro [(35)S]-GTP-γ-S assays.

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