Synthesis of 11-hydroxyl O-methylsterigmatocystin and the role of a cytochrome P-450 in the final step of aflatoxin biosynthesis
Synthesis of 11-hydroxyl O-methylsterigmatocystin and the role of a cytochrome P-450 in the final step of aflatoxin biosynthesis
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DOI：
10.1021/ja012185v
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发表时间：
2002-05-15
影响因子：
15
通讯作者：
Townsend, CA
中科院分区：
文献类型：
--
作者：
Udwary, DW;Casillas, LK;Townsend, CA
黄曲霉毒素B-1复杂生物合成过程中的主要骨架重排(蒽醌-黄原酮-香豆素)由细胞色素P-450介导。以前的实验表明，将X-酮O-甲基杂色曲霉毒素(OMST)转化为黄曲霉毒素需要两个连续的单加氧酶反应，我们证明这个过程是由一个P-450，Orda介导的。与在黄曲霉中的发现一致，第一个氧化循环导致11-羟基O-甲基杂色曲霉毒素(HOMST)的形成，而第二个氧化循环需要芳环裂解、去甲基化、脱水、脱羧基和重排，从而使黄曲霉毒素发生一系列显著的转化。为了验证这一假设，HOMST是由Houben-Hoesch反应的烷基氮变体合成的。以丁烯的形式保护麻烦的xanthone羰基，以便进一步精制分子，然后在独特的易得的过酸脱除保护中恢复产物xanthone。设计了构建灵敏的二氢双呋喃和维持部分甲基化对苯二酚的氧化状态的方法。在酵母膜制剂中表达ORDA使HOMST在OMST转化为黄曲霉毒素的过程中被检测到，并直接在霉菌毒素的生物合成中被建立。在确定了HOMST在黄曲霉毒素形成中的作用后，我们考虑了这个P-450的第二个氧化循环的机制。
The major skeletal rearrangements (anthraquinone - xanthone - coumarin) that occur in the complex biosynthesis of aflatoxin B-1 are mediated by cytochromes P-450. Previous experiments have suggested that two successive monooxygenase reactions are required to convert the xanthone O-methylsterigmatocystin (OMST) to aflatoxin, a process we demonstrate is mediated by a single P-450, OrdA, in Aspergillus parasiticus in accord with findings in A. flavus, The first oxidative cycle is proposed to result in the formation of 11-hydroxy O-methylsterigmatocystin (HOMST), while the second entails aryl ring cleavage, demethylation, dehydration, decarboxylation, and rearrangement to give aflatoxin - a remarkable sequence of transformations. To test this hypothesis, HOMST has been synthesized by an alkylnitrilium variant of the Houben-Hoesch reaction. The troublesome xanthone carbonyl was protected as a butylene to allow further elaboration of the molecule, and then the product xanthone was restored in a uniquely facile peracid deprotection. Methods were devised to construct the sensitive dihydrobisfuran and to maintain the oxidation state of the partially methylated hydroquinone. Expression of ordA in a yeast membrane preparation enabled the intermediacy of HOMST both to be detected in the conversion of OMST to aflatoxin and to be established directly in the biosynthesis of the mycotoxin. Having secured the role of HOMST in aflatoxin formation, the mechanism of the second oxidative cycle of this P-450 is considered.