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Enzyme-catalysed [4+2] cycloaddition is a key step in the biosynthesis of spinosyn A

机译:酶催化的[4 + 2]环加成反应是多杀菌素A生物合成的关键步骤

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The Diels-Alder reaction is a [4+2] cycloaddition reaction in which a cyclohexene ring is formed between a 1,3-diene and an electron-deficient alkene via a single pericyclic transition state1. This reaction has been proposed as a key transformation in the biosynthesis of many cyclohexene-containing secondary metabolites. However, only four purified enzymes have thus far been implicated in bio-transformations that are consistent with a Diels-Alder reaction, namely solanapyrone synthase, LovB, macrophomate synthase, and riboflavin synthase. Although the stereochemical outcomes of these reactions indicate that the product formation could be enzyme-guided in each case, these enzymes typically demonstrate more than one catalytic activity, leaving their specific influence on the cycloaddition step uncertain. In our studies of the biosynthesis of spinosyn A, a tetracyclic polyketide-derived insecticide from Saccharopolyspora spinosa, we identified a cyclase, SpnF, that catalyses a transannular [4+2] cycloaddition to form the cyclohexene ring in spinosyn A. Kinetic analysis demonstrates that SpnF specifically accelerates the ring formation reaction with an estimated 500-fold rate enhancement. A second enzyme, SpnL, was also identified as responsible for the final cross-bridging step that completes the tetracyclic core of spinosyn A in a manner consistent with a Rauhut-Currier reaction. This work is significant because SpnF represents the first example characterized in vitro of a standalone enzyme solely committed to the catalysis of a [4+2] cycloaddition reaction. In addition, the mode of formation of the complex perhydro-as-indacene moiety in spinosyn A is now fully established.
机译:Diels-Alder反应是一种[4 + 2]环加成反应,其中环己烯环通过一个单一的周环过渡态在1,3-二烯与缺电子的烯烃之间形成环己烯环。已经提出该反应是许多含环己烯的次级代谢物生物合成中的关键转化。然而,迄今为止,仅四种纯化的酶参与了与狄尔斯-阿尔德反应一致的生物转化,即茄那酮合酶,LovB,大膦酸酯合酶和核黄素合酶。尽管这些反应的立体化学结果表明在每种情况下产物的形成都可以由酶引导,但是这些酶通常表现出一种以上的催化活性,从而不确定其对环加成步骤的具体影响。在我们的生物合成棘孢菌素A的生物合成研究中,该菌素是源自棘糖多孢菌的四环聚酮化合物衍生的杀虫剂,我们鉴定了环化酶SpnF,该酶催化跨环的[4 + 2]环加成反应在Spinosyn A中形成环己烯环。动力学分析表明, SpnF特异性地加速了成环反应,速率提高了500倍。还鉴定出第二种酶SpnL负责最终的跨桥步骤,该步骤以与Rauhut-Currier反应一致的方式完成了多杀菌素A的四环核心。这项工作意义重大,因为SpnF代表了第一个实例,该实例在体外表征了仅致力于催化[4 + 2]环加成反应的独立酶。另外,现在完全确立了在多杀菌素A中复杂的过氢-如-茚并二烯部分的形成方式。

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  • 来源
    《Nature》 |2011年第7345期|p.109-112|共4页
  • 作者单位

    Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA;

    Division of Medicinal Chemistry, College of Pharmacy, University of Texas at Austin, Austin, Texas 78712, USA;

    Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA;

    Division of Medicinal Chemistry, College of Pharmacy, University of Texas at Austin, Austin, Texas 78712, USA;

    Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA,Division of Medicinal Chemistry, College of Pharmacy, University of Texas at Austin, Austin, Texas 78712, USA;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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