Koepp A E, Hezari M, Zajicek J, Vogel B S, LaFever R E, Lewis N G, Croteau R
Institute of Biological Chemistry, Washington State University, Pullman 99164-6340, USA.
J Biol Chem. 1995 Apr 14;270(15):8686-90. doi: 10.1074/jbc.270.15.8686.
The biosynthesis of taxol (paclitaxel) and related taxoids in Pacific yew (Taxus brevifolia) is thought to involve the cyclization of geranylgeranyl diphosphate to a taxadiene followed by extensive oxygenation of this diterpene olefin intermediate. A cell-free preparation from sapling yew stems catalyzed the conversion of [1-3H]geranylgeranyl diphosphate to a cyclic diterpene olefin that, when incubated with stem sections, was converted in good radiochemical yield to several highly functionalized taxanes, including 10-deacetyl baccatin III and taxol itself. Addition of the labeled olefin to a yew bark extract, followed by radiochemically guided fractionation, provided sufficient product to establish the structure as taxa-4(5),11(12)-diene by two-dimensional NMR spectroscopic methods. Therefore, the first dedicated step in taxol biosynthesis is the conversion of the universal diterpenoid precursor geranylgeranyl diphosphate to taxa-4(5),11(12)-diene, rather than to the 4(20),11(12)-diene isomer previously suggested on the basis of the abundance of taxoids with double bonds in these positions. The very common occurrence of taxane derivatives bearing the 4(20)-ene-5-oxy functional grouping, and the lack of oxygenated derivatives bearing a 4(5)-double bond, suggest that hydroxylation at C-5 of taxadiene with allylic rearrangement of the double bond is an early step in the conversion of this olefin intermediate to taxol.
太平洋紫杉（短叶红豆杉）中紫杉醇（紫衫醇）及相关紫杉烷类化合物的生物合成被认为涉及到牻牛儿基牻牛儿基二磷酸环化生成紫杉二烯，随后该二萜烯烃中间体发生广泛的氧化反应。来自幼龄紫杉茎的无细胞制剂催化了[1-³H]牻牛儿基牻牛儿基二磷酸转化为一种环状二萜烯烃，当与茎段一起孵育时，该烯烃以良好的放射化学产率转化为几种高度官能化的紫杉烷类化合物，包括10-去乙酰基浆果赤霉素III和紫杉醇本身。将标记的烯烃添加到紫杉树皮提取物中，随后进行放射化学导向分级分离，得到了足够的产物，通过二维核磁共振光谱法确定其结构为紫杉-4(5),11(12)-二烯。因此，紫杉醇生物合成中的第一个特定步骤是将通用的二萜前体牻牛儿基牻牛儿基二磷酸转化为紫杉-4(5),11(12)-二烯，而不是先前基于这些位置具有双键的紫杉烷类化合物的丰度所推测的4(20),11(12)-二烯异构体。具有4(20)-烯-5-氧基官能团的紫杉烷衍生物非常常见，而缺乏具有4(5)-双键的氧化衍生物，这表明紫杉二烯C-5位的羟基化以及双键的烯丙基重排是该烯烃中间体转化为紫杉醇的早期步骤。
