Taxadiene Synthase-Catalyzed Cyclization of 6-Fluorogeranylgeranyl Diphosphate to 7-Fluoroverticillenes
作者:Yinghua Jin、David C. Williams、Rodney Croteau、Robert M. Coates
DOI:10.1021/ja050592r
日期:2005.6.1
The mechanism of the taxadiene synthase-catalyzed cyclization of (E,E,E)-geranylgeranyl diphosphate (GGPP, 7) to taxadiene (5) is proposed to proceed through a verticillen-12-yl carbocation intermediate (8) that undergoes an 11 --> 7 proton transfer leading to formation of the C ring. The substrate analogue 6-fluoroGGPP (17) was synthesized to elucidate the stereochemistry of the putative verticillenyl
紫杉二烯合酶催化的 (E, E, E)-香叶基香叶基二磷酸酯 (GGPP, 7) 环化为紫杉二烯 (5) 的机制被提议通过 verticillen-12-yl 碳阳离子中间体 (8) 进行,该中间体经过 11 --> 7 个质子转移导致 C 环的形成。合成底物类似物 6-氟 GGPP (17) 以阐明推定的轮枝菌基中间体的立体化学。预计氟取代基的感应吸电子效应会阻止临界质子转移到 Delta(7) 双键,从而破坏双环阶段的环化。根据 GC/MS 分析,氟类似物与重组紫杉二烯合酶的孵育产生了三种主要和两种次要氟二萜的混合物。三种主要产物被确定为环外、环内和 4(20)-亚甲基 7-氟硅烯,即 Delta(3,7,12 (18))、Delta(3,7,12) 和 Delta(4) (20),7,11) 异构体(22、23 和 24)基于 (1) H NMR 分析和与母体双环二萜的比较。通过 NOE