Biosynthesis of Erythrina alkaloids in Erythrina crista-galli

A precursor application system was developed to allow the study of Erythrin a alkaloid formation in Erythrina crista-galli. Fruit wall tissue of this s pecies was recognized as the major site of alkaloid biosynthesis. The appli cation of radioactively and C-13-labelled potential precursors showed that the hitherto assumed precursor (S)-norprotosinomenine was not incorporated into the Erythrina alkaloids. In contrast, (S)-coclaurine as well as (S)-no rreticuline were metabolized to erythraline and erythrinine, respectively, suggesting that a coclaurine-norreticuline pathway is operative in Erythrin a alkaloid formation. Feeding of [1-C-13]-labelled (S)-norreticuline with s ubsequent NMR spectroscopy demonstrated that the resulting erythraline was exclusively labelled at position C-10. Therefore, the participation of a sy mmetrical intermediate of the diphenoquinone type in Erythrina alkaloid bio synthesis can be excluded. (C) 1999 Elsevier Science Ltd. All rights reserv ed.