Abstract
AbstractThe 13C NMR spectra of the isomeric alkaloids lupinine and epilupinine and their perchlorates, methiodides and N‐oxides are discussed. Chemical shift changes due to protonation, quaternization and N‐oxidation are analysed. The trans‐quinolizidine ring fusion is proved for epilupinine salts and for the N‐oxide. Lupinine also exists predominantly with the trans ring fusion, but the cis ring fusion is found in the methiodide. An equilibrium of two stereoisomers, one with trans‐ and the other with cis‐ring fusion, has been established for lupinine perchlorate in D2O solution. Lupinine N‐oxides isolated in the crystalline state are shown to have both trans‐ and the cis‐ring fusion.
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