Structure and Reactivity of the Dammarenyl Cation: Configurational Transmission in Triterpene Synthesis
作者:Quanbo Xiong、Flavio Rocco、William K. Wilson、Ran Xu、Maurizio Ceruti、Seiichi P. T. Matsuda
DOI:10.1021/jo050147e
日期:2005.7.1
The dammarenyl cation (13) is the last common intermediate in the cyclization of oxidosqualene to a diverse array of secondary triterpene metabolites in plants. We studied the structure and reactivity of 13 to understand the factors governing the regio- and stereospecificity of triterpene synthesis. First, we demonstrated that 13 has a 17β side chain in Arabidopsis thaliana lupeol synthase (LUP1) by
达玛烯基阳离子(13)是氧化角鲨烯环化成植物中各种次级三萜代谢物的最后一个常见中间体。我们研究了13的结构和反应性,以了解控制三萜合成的区域和立体特异性的因素。首先,我们通过将底物类似物(18 E)-22,23-dihydro-20-oxaoxidosqualene(21)与不含酵母的重组酵母菌株中的LUP1一起孵育,证明13在拟南芥狼毒醇合成酶(LUP1)中具有17β侧链。其他环化酶并显示21的唯一产物为3β-羟基-22,23,24,25,26,27-hexanor-17β-dammaran-20-one。在气相模型上进行了量子力学计算,结果表明20-氧杂取代对底物结合和导致C17差向异构体13的反应活化能的影响可忽略不计。进一步的分子建模表明,由于环化酶活性位点腔中的旋转自由度有限,四环中间体13的C17构型可以从五环或6--6-6-6四环产物的角甲基构型推导。构型传递的这一规则有助于