Stereochemistry of quinolizidine alkaloid biosynthesis: incorporation of the enantiomeric [2-2H]cadaverines into lupinine

Samples of (R)- and (S)-[2-2H]cadaverines 10 and 12 prepared from L and D-glutamic acid, respectively, were fed to Lupinus luteus plants and the labelling patterns in lupinine 1 determined by 2H NMR spectroscopy demonstrated that the quinolizidine ring system is formed by removal of the pro-S hydrogen and retention of the pro-R hydrogen at C-1 of lupinine.