The biosynthesis of retronecine

Abstract
An experiment with putrescine, doubly labeled intramolecularly, with 15N and 13C at the adjacent C-atom, demonstrated that a C4-N-C4 compound with C2v symmetry serves as a precursor of retronecine, the most common base of the Senecio alkaloids. The C4-N-C4 compound is generated from 2 ornithine-derived precursor units. This was demonstrated by a degradation sequence whereby the distribution of label from [5-14C]-,[5-3H]- and [4-3H]ornithine within retronecine was studied.