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

Abstract

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 C_2v symmetry, such as (10), is not involved in lupinine or sparteine biosynthesis.