Biosynthesis of anthraquinones in cell cultures of Cinchona 'Robusta' proceeds via the methylerythritol 4-phosphate pathway

Robustaquinone B was found as a major anthraquinone in cell cultures of Cinchona 'Robusta' after treatment with a fungal elicitor. Anthraquinones in Cinchona are considered to be of the Rubia type, i.e. rings A and B are derived from chorismate and alpha-ketoglutarate, whereas ring C is formed from isopentenyl diphosphate (IPP). To determine the origin of IPP, either formed via the mevalonic acid pathway or the 2-C-methyl-D-erythritol 4-phosphate pathway, the incorporation of [1-C-13]glucose into robustaquinone B was studied. The C-13 labeling of robustaquinone B was analyzed by one- and two-dimensional NMR spectroscopy and the labeling pattern was compared with the hypothetical labeling patterns obtained via the different biosynthetic pathways. The results clearly show that the IPP, constituting the ring C of robustaquinone B, is biosynthesized via the 2-C-methyl-D-erythritol 4-phosphate pathway. Moreover, the data also confirm that rings A and B of robustaquinone B are formed from chorismate and alpha-ketoglutamate via o-succinylbenzoate. (C) 2002 Elsevier Science Ltd. All rights reserved.