Application of 2H n.m.r. spectroscopy to study the incorporation of enantiomeric 2H-labelled cadaverines into quinolizidine alkaloids
The biosynthesis of a number of quinolizidine alkaloids has been studied in two Lupinus species using cadaverine precursors chirally labelled with deuterium. The labelling patterns in lupinine (2), sparteine (3), lupine (6), and angustifoline (8), derived biosynthetically from (R)-[1-2H]-(11) and (S)-[1-2H]cadaverine (12) have been established by 2H n.m.r. spectroscopy. The stereochemistry of a number of the steps involved in the conversion of cadaverine into lupinine (2) and the tetracyclic quinolizidine alkaloids has been established. The presence of 2H at C-17 in samples of sparteine (3), lupanine (6), and angustifoline (8) derived from the (R)-isomer (11) demonstrates that 17-oxosparteine (9) cannot be an intermediate in the biosynthesis of tetracyclic quinolizidine alkaloids. The presence of 2H at C-2 in both samples of sparteine (3) after feeding the precursors (11) and (12) disproves the theory that lupanine (6) is a precursor of sparteine (3).