1H and 13C NMR studies on the conformation of E,Z-diastereomers of N-desmethyl-N,O-diacetyl-α-metazocine (sp2-hybridized nitrogen derivatives of a benzomorphan narcotic analgesic)
✍ Scribed by Robert Glaser; Michael A. Bernstein; Ayala Balan
- Publisher
- John Wiley and Sons
- Year
- 1991
- Tongue
- English
- Weight
- 768 KB
- Volume
- 29
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
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.