Application of 13C n.m.r. spectroscopy to study the biosynthesis of the quinolizidine alkaloids lupinine and sparteine

The labelling patterns in (–)-sparteine (14) and (–)-lupinine (15) derived biosynthetically from [1-amino-15N,1-13C]cadaverine dihydrochloride (13) have been established by 13C n.m.r. spectroscopy. Three units of (13) are incorporated to about the same extent into sparteine, and two 13C-15N doublets are observed in the 13C{1H} n.m.r. spectrum of sparteine, demonstrating that two of these cadaverine units are converted into the outer rings of sparteine in a specific fashion. Two cadaverine (13) units are incorporated into lupinine (15) and one 13C-15N doublet is observed. These results, and 14C-labelling experiments with 1,7,13-triazatridecane (10) indicate that a later C5–N–C5 intermediate with C2v symmetry, such as (10), is not involved in lupinine or sparteine biosynthesis.