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

Abstract

The 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 andysed. The trans-quinolizidine ring fusion is proved for epilupinine salts and for the N-oxide. hpinine also exists predominantly with the trans ring fusion, but the cis ring fusion is found in the methiodide. An equiliirium of two stereoisomers, one with tram-and the other with cis-ring fusion, has been established for lupinine perchlorate in D20 solution. Lupinine N-oxides isolated in the crystalline state are shown to have both trans-and the cis-ring fusion.

Rotational Spectra of Bicyclic Decanes: The Trans Conformation of (−)-Lupinine

“…However, other authors have argued that a small IR band associated to free OH would imply the simultaneous existence of rotamers . No evidence of an intramolecular hydrogen bond was found in the crystal analysis, but there are no high-resolution spectroscopic studies, except for the 13 C NMR spectrum. , …”

“…9 No evidence of an intramolecular hydrogen bond was found in the crystal analysis, but there are no highresolution spectroscopic studies, except for the 13 C NMR spectrum. 10,11 In order to solve the conformational issues on (−)-lupinine, we examined its rotational spectrum using Fourier-transform microwave (FT-MW) spectroscopy 12−14 in a near-adiabatic supersonic expansion. This technique is capable of providing isotopically sensitive structural information and intramolecular dynamics for polar molecules and weakly bound intermolecular clusters of moderate size (<∼30 heavy atoms).…”

Biosynthesis of the lupine alkaloids. I. Lupinine

“…The less intense set of signals shows two signals at 6 40.0 and 44.6 ppm. Signals in this spectral region are absent from the spectra of the trans fused free base (14)(15)(16)(17)(18) or the trans fused salt (15) but are present in the cis fused salt (15). The signal set of lower intensity is thus due to the cis fused salt, which is the less abundant (ca.…”