Fluoro-α-amino acids. 1—use of 19F NMR spectroscopy for the configurational determination of β-fluoro-α-amino acids through complexation by 18-crown-6 ether
✍ Scribed by S. Hamman; M. C. Salon; C. Béguin
- Publisher
- John Wiley and Sons
- Year
- 1982
- Tongue
- English
- Weight
- 522 KB
- Volume
- 20
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
Abstract
Erythro and threo configurational assignments have been made for 11 β‐fluoro‐α‐amino acids or esters using the effect of complexation of the ammonium group by 18‐crown‐6 ether on the ^19^F NMR parameters. For the erythro configurations, ^3^J(HF) increases and a high‐field ^19^F chemical shift is generally observed; these phenomena are accompanied by a decrease in ^3^J(HH) and ^3^J(CF). The opposite effects are observed for the threo configurations. These observations can be explained by a change in the relative population of the conformers around the Cα‐Cβ bond on complexation of the ammonium group. This complexation impairs the interactions between the ammonium and fluorine groups and, concomitantly, the steric hindrance between the ammonium and R (methyl, phenyl or carboxylate) groups is increased.