Taxus metabolomic study and the elucidation of the taxane biosynthetic framework in Taxus root

The medicinal plant Taxus (Taxaceae), an important source of a series of biological active compounds including anticancer agent paclitaxel and its analogs, has drawn much attention and been under intense investigation during the past fifty years. Paclitaxel and its semi-synthetic precursors belong to a group of typical secondary metabolites named the taxane diterpenoids or taxoids, but their distribution and level are very variable with species, tissue, and growing conditions. In order to explore the differences in accumulation and in distribution of metabolites in various Taxus species, an efficient and sensitive profiling approach to complex yew samples was developed using ultra-performance liquid chromatography-electrospray ionization mass spectrometry (UPLC-ESI-MS) in this study. The appropriate in-source CID energy was employed to produce informative characteristic ions which could be used for stereochemical and sub-structural assignment of yew constituents. The method was successfully applied in rapid screening of Taxus needle and root samples from various species including T. yunnanensis, T. chinensis, T. mairei, T. × media, T. cuspidata, T. wallichiana, and T. canadensis. Most yew constituents can be characterized based on the fragment behavior of model compounds, and fifty-three constituents including forty-seven taxoids were detected from Taxus root extract. It is evident from the metabolic profiling results that root samples from different Taxus species have similar profile and nearly identical chemical distribution, which suggests that Taxus roots have similar metabolic frameworks. In sharp contrast, needle extracts from various Taxus species displayed significant metabolic variations both in chemical distribution and in concentration. It is also very impressing that thirty-three taxoids with 10-DAB skeleton existed in Taxus root, which can be used as semi-synthetic precursors for paclitaxel. These taxoids are also recognized as intermediates or products involved in parallel pathways of paclitaxel formation via the important intermediate 10-DAB during taxane biosynthesis. On the basis of the appearance and connectivity of all detected taxanes in Taxus root, the down-stream biosynthetic framework in Taxus roots was explored in combination of related information on taxane biosynthesis. Additionally, Taxus root resources also display benign medicinal perspective, due to the high yield of valuable taxanes including paclitaxel, cephalomannine, 10-deacetylpaclitaxel and 7-xylosyltaxanes in this tissue. The proposed UPLC-based profiling method is suitable for large-scale screening of crude yew samples and can be applied in quality control and metabolic study of this uncommon plant. This study also can promote further studies on plant metabolomics and on sustainable utilization of Taxus resources.