LATE STAGES IN THE BIOSYNTHESIS OF AUCUBIN IN SCROPHULARIA

Deuterium-labelled samples of 8-epi-deoxyloganic acid, deoxygeniposidi c acid, geniposidic acid. and bartsioside (6-deoxyaucubin) all gave hi gh incorporations into aucubin in Scrophularia umbrosa whereas labelle d 6,10-dideoxyaucubin did not give a significant incorporation. In S. racemosa, 8-epi-deoxyloganic acid gave a high incorporation into aucub in and harpagide while 8-epi-loganic acid was not incorporated. Diluti on experiments with labelled 8-epi-deoxyloganic acid and unlabelled ge niposidic acid or scandoside showed that geniposidic acid is an interm ediate in the biosynthesis of aucubin whereas scandoside apparently is not. The pathway from 8-epi-deoxyloganic acid to aucubin has thus bee n established, showing that decarboxylation takes place at the genipos idic acid stage.