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Complete proton and carbon nuclear magnetic resonance spectral assignments of some morphinan‐6‐one alkaloids by two‐dimensional NMR techniques
Author(s) -
Caldwell Gary W.,
Gauthier A. Diane,
Mills John E.,
Greco Michael N.
Publication year - 1993
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260310318
Subject(s) - chemistry , proton magnetic resonance , nuclear magnetic resonance , proton nmr , proton , stereochemistry , nuclear physics , physics
The 1 H (400 MHz) and carbon 13 C (100 MHz) NMR peak assignments of two oxymorphone alkaloids including the free base and the hydrochloride (HCl) salt and four oxycodone alkaloids including the free base, the HCl salt, the N ‐oxide and the methyl iodide quaternary salt were assigned using a variety of two‐dimensional NMR techniques. Proton coupling constants provide evidence that the cyclohexanone (D) and the piperidine (E) rings adopt slightly distorted chair conformations. Nuclear Overhauser enhancement difference experiments indicate that the conformation of the N ‐methyl group is equatorial and the O ‐methyl group prefers a cis orientation relative to C‐2. The minor component observed in aqueous 1 H and 13 C NMR spectra of each HCl salt and the N ‐oxide is produced by the reaction of the alkaloid with water at the C‐6 carbonyl, forming a gem ‐diol, and is not due to the presence of the axial isomer. The first complete solution and solid conformational analyses of oxycodone N ‐oxide by NMR and x‐ray crystallography have been investigated. The data indicate that the C‐14‐OH proton is intramolecularly hydrogen bonded to the NO oxygen.