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1 H and 13 C NMR studies on the conformation of E , Z ‐diastereomers of N ‐desmethyl‐ N , O ‐diacetyl‐α‐metazocine (sp 2 ‐hybridized nitrogen derivatives of a benzomorphan narcotic analgesic)
Author(s) -
Glaser Robert,
Bernstein Michael A.,
Balan Ayala
Publication year - 1991
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.1260290805
Subject(s) - chemistry , piperidine , diastereomer , dihedral angle , stereochemistry , ring (chemistry) , vicinal , chemical shift , cyclohexane conformation , nmr spectra database , proton nmr , coupling constant , amide , moiety , crystallography , hydrogen bond , molecule , spectral line , organic chemistry , physics , particle physics , astronomy
Abstract The 1 H (300 MHz) and 13 C (75.5 MHz) NMR spectra (CDCl 3 ) of N ‐desmethyl‐ N , O ‐diacetyl‐α‐metazocine showed two ( E , Z )‐amide diastereomers (ratio ≈ 1 : 2, respectively). All four vicinal proton‐proton coupling constants in each NCH 2 CH 2 C moiety were readily measured owing to effective chemical shift dispersion caused by the acetamido function. All vicinal coupling constants were also measured in the E. COSY 2D NMR spectrum. Comparison of the vicinal coupling constants involving sp 2 ‐N piperidine ring protons in the ( E , Z )‐amides and the corresponding values involving sp 3 ‐N piperidine ring protons in morphine free base and hydrochloride N ‐methyl diastereomers shows them to be similar. The R ‐factor method was used to estimate a 54(1)° value for the N CH 2 CH 2 C dihedral angle in the sp 2 ‐N piperidine ring for both solution‐state E , Z ‐diasteromers. The corresponding dihedral angle within the sp 3 ‐N piperidine ring in solid‐state (±)‐6‐desmethyl‐8‐deoxy‐α‐metazocine · HCl was found to be 53.8° by x‐ray crystallography. Both sp 2 and sp 3 N‐hybridrization seem to afford basically the same slightly flattened chair‐type conformations for the piperidine‐ring.