Terpenoid Biosynthesis from 1-Deoxy-D-Xylulose in Higher Plants by Intramolecular Skeletal Rearrangement

The incorporation of [1-¹³C]- and [2,3,4,5-¹³C₄]1-deoxy-D-xylulose into β-carotene, lutein, phytol, and sitosterol in a cell culture of Catharanthus roseus was analyzed by NMR spectroscopy. The labeling patterns of the isoprene precursors, isopentenyl pyrophosphate and dimethylallyl pyrophosphate, were obtained from the terpenes by a retrobiosynthetic approach. ¹³C Enrichment and ¹³C¹³C coupling patterns showed conclusively that 1-deoxy-D-xylulose and not mevalonate is the predominant isoprenoid precursor of phytol, β-carotene, and lutein. Label from 1-deoxyxylulose was also diverted to phytosterols to a minor extent (6% relative to carotene and phytol formation). The data demonstrate that the formation of isopentenyl pyrophosphate from pentulose occurs strictly by an intramolecular rearrangement process.