Hiroshi Okumoto

Cloning and Characterization of the 2-C-Methyl-D-erythritol 4-Phosphate (MEP) Pathway Genes of a Natural-Rubber Producing Plant, Hevea brasiliensis

Natural rubber is synthesized as rubber particles in the latex, the fluid cytoplasm of laticifers, of Hevea brasiliensis. Although it has been found that natural rubber is biosynthesized through the mevalonate pathway, the involvement of an alternative 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway is uncertain. We obtained all series of the MEP pathway candidate genes by analyzing expressed sequence tag (EST) information and degenerate PCR in H. brasiliensis. Complementation experiments with Escherichia coli mutants were performed to confirm the functions of the MEP pathway gene products of H. brasiliensis together with those of Arabidopsis thaliana, and it was found that 1-deoxy-D-xylulose-5-phosphate reductoisomerase, 2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase, and 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase of H. brasiliensis were functionally active in the E. coli mutants. Gene expression analysis revealed that the expression level of the HbDXS2 gene in latex was relatively high as compared to those of other MEP pathway genes. However, a feeding experiment with [1-13C] 1-deoxy-D-xylulose triacetate, an intermediate derivative of the MEP pathway, indicated that the MEP pathway is not involved in rubber biosynthesis, but is involved in carotenoids biosynthesis in H. brasiliensis.

Biosynthetic Pathway for the C45 Polyprenol, Solanesol, in Tobacco

Feeding experiments were independently performed with [1-13C]deoxy-D-xylulose triacetate and (RS)-[2-13C]mevalonolactone in the tobacco plant. The labeling pattern for solanesol was elucidated to reveal that the isoprene moiety of solanesol would be derived from deoxy-xylulose. The result strongly suggests that tobacco solanesol is biosynthesized via the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway.

Contribution of Mevalonate and Methylerythritol Phosphate Pathways to Polyisoprenoid Biosynthesis in the Rubber-Producing Plant Eucommia ulmoides Oliver

The biosynthetic origin of isopentenyl diphosphate in the polyisoprenoid biosynthesis of the rubber-producing plant Eucommia ulmoides Oliver was elucidated for the fi rst time by feeding experiments using 13C-labeled isotopomers of (RS)-mevalonate, 1-deoxy-D-xylulose- 3,4,5-triacetate, 2C-methyl-D-erythritol-1,2,3,4-tetraacetate, and pyruvate. After 13C-labeled isotopomers were fed to the young seedlings, the polyisoprenoid fractions were prepared and analyzed by 13C NMR. The NMR data showed that the isoprene units of polyisoprenoid derived from isopentenyl diphosphate, which was biosynthesized using both mevalonate and 1-deoxy-D-xylulose-5-phosphate in E. ulmoides. It is assumed that the cross-talk of isopentenyl diphosphate, derived from both pathways, occurs during the biosynthesis of polyisoprenoid; therefore, it was observed in the formation of low-molecular weight isoprenoids.

A semisynthesis of paclitaxel via a 10-deacetylbaccatin III derivative bearing a β-keto ester appendage

Abstract A semisynthesis of paclitaxel has successfully been accomplished starting from a newly developed baccatin III derivative bearing a β-keto ester appendage on C-13.

Synthesis of new baccatin III derivatives through transesterification of β-keto esters with a protected 10-deacetylbaccatin III

Abstract Synthesis of a new array of baccatin III derivatives bearing a β-keto ester appendage on C-13 is successfully achieved through transesterification of a wide range of β-keto esters with a protected baccatin III.