Determining C-7 stereochemistry in C-7-substituted 6α,14α-endo-ethano- and 6α, 14α-endo-ethenotetrahydrothebaines by 13C NMR; a re-analysis
✍ Scribed by Samuel M. Mazza
- Publisher
- John Wiley and Sons
- Year
- 1993
- Tongue
- English
- Weight
- 231 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0749-1581
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
A re‐analysis of previously published ^13^C NMR data on C‐7‐substituted 6α,14α‐endo‐ethanotetrahydrothebaines shows that the ^13^C chemical shift of C‐18 in these medicinally important compounds can be used as an indicator of C‐7 stereochemistry, this being due to a steric gamma effect between C‐18 and C‐7 substituents in an α orientation. In seven examples of α‐isomers the C‐18 chemical shift ranges from δ17.02 to δ18.42 (average δ17.72), whereas in four examples of β‐isomers the C‐18 chemical shift ranges from δ22.09 to δ24.00 (average δ22.73‐23.40). Since suitable etheno compounds can be chemically reduced to ethano compounds, C‐7 stereochemistry in such 6α,14α‐endo‐etheno compounds can be determined indirectly.