¹³C NMR spectroscopic study of lupinine and epilupinine salts and amine oxides

Abstract

Abstract The 13 C 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 D 2 O solution. Lupinine N ‐oxides isolated in the crystalline state are shown to have both trans ‐ and the cis ‐ring fusion.