(10% paclitaxel content) and then to Canada for further purification to 95% purity. The semisynthesis to final product takes place in China. Biosynthesis The biosynthetic pathway to paclitaxel has been investigated and consists of approximately 20 enzymatic steps. The complete scheme is still unavailable. The segments that are known are very different from the synthetic pathways tried thus far (Scheme 1). The starting compound is geranylgeranyl diphosphate 2 which is a dimer of geraniol 1. This compound already contains all the required 20 carbon atoms for the paclitaxel skeleton. More ring closing through intermediate 3 (taxadiene) leads to taxusin 4. The two main reasons why this type of synthesis is not feasible in the laboratory is that nature does a much better job controlling stereochemistry and a much better job activating a hydrocarbon skeleton with oxygen substituents for which cytochrome P450 is responsible in some of the oxygenations. Intermediate 5 is called 10-deacetylbaccatin III. A biochemical kilogram-scale production of taxadiene was reported using genetically engineered E. coli in 2011. References and notes External links Paclitaxel Total Syntheses @ SynArchive.com Taxolog for Taxol research, founded by Holto The complete Taxol story from Chemical & Engineering News: Article Extensive Florida State University article Story of taxol total synthesis Total synthesis Taxanes