Opioid conformations: The remarkable effect of C‐14 substituents on ring c conformations of 6α and 6β epimers of 6‐substituted epoxymorphinan opioid ligands

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Abstract
High field1H nmr studies have shown that the nature of theC‐14 substituents has a remarkable influence on ringCconformation of epoxymorphinan opioids which have a 6α‐hydroxyl group. In sharp contrast to the ringCtwist‐boat conformation observed in those 6α‐hydroxy compounds which also have a 14‐hydroxyl group (α‐naltrexol; α‐oxymorphol), ringCexists predominantly as a chair conformer in 6α‐hydroxy compounds which have a proton bound toC‐14 (dihydromorphine; dihydrocodeine). The 6β‐hydroxy compounds (β‐naltrexol; β‐oxymorphol) have a ringCchair conformation in agreement with earlier studies.