Optical rotation of quinolizidine alkaloids: An important variable in chemosystematic studies of Fabaceae

The anomalous distribution of (+)-lupanine and (-)-lupanine in Podalyria species provides circumstantial evidence that hydroxylation and subsequent esterification of lupanine is only possible when (-)-sparteine and (+)-lupanine are the precursors. The optical rotation of lupanine and/or sparteine isolated from different genera, in combination with literature data, provide evidence of a separate biosynthetic pathway which leads to lupanine-type esters rather than α-pyridones. The occurrence of this pathway can be predicted from the optical rotation of sparteine and/or lupanine, even in the absence of end products. Enantiomers-specificity is thus an important variable for establishing homology in comparative studies.