Cyclopropyl containing fatty acids as mechanistic probes for cytochromes P450
Cyclopropyl containing fatty acids as mechanistic probes for cytochromes P450
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DOI：
10.1021/jo047985d
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发表时间：
2005-04-01
影响因子：
3.6
通讯作者：
De Voss, JJ
中科院分区：
文献类型：
--
作者：
Cryle, MJ;de Montellano, PRO;De Voss, JJ
细胞色素P450的脂肪族羟基化机制一直是激烈争论的主题，提出了几种替代机制。各种含环丙基的化合物（自由基时钟）在氧化后可以产生未重排和开环产物，一直是这些研究的关键工具。本研究中，我们介绍了几种含环丙基的脂肪酸1a-4a，以探讨P450能够脂肪酸羟基化的机制。探针被证明是能够区分自由基的阳离子中间体由于异构环丙基阳离子的快速平衡。自由基中间体在氧化转化中的开环预期产生单个重排的醇，而阳离子在开环之前异构化，产生两个异构的高烯丙醇。通过P450（BM 3）和P450（Biol）氧化这些探针得到的结果与通过这些酶的脂肪酸羟基化中的自由基而不是阳离子中间体一致。未重排和开环产物的定量给出了（2-3）× 10（10）s（-1）的氧反弹率。讨论了脂肪酸中引入环丙烷环对羟基化反应区域化学的影响。
The mechanism of aliphatic hydroxylation by cytochromes P450 has been the subject of intense debate with several proposed mechanistic alternatives. Various cyclopropyl containing compounds (radical clocks), which can produce both unrearranged and ring opened products upon oxidation, have been key tools in these investigations. In this study, we introduce several cyclopropyl containing fatty acids 1a-4a with which to probe the mechanism of P450s capable of fatty acid hydroxylation. The probes are shown to be capable of distinguishing radical from cationic intermediates due to the rapid equilibration of isomeric cyclopropyl cations. Ring opening of a radical intermediate in an oxidative transformation is expected to yield a single rearranged alcohol, whereas a cation isomerizes prior to ring opening, leading to two isomeric homoallylic alcohols. Oxidation of these probes by P450(BM3) and P450(Biol) gives results consistent with a radical but not a cationic intermediate in fatty acid hydroxylation by these enzymes. Quantitation of the unrearranged and ring opened products gives remarkably homogeneous rates for oxygen rebound of (2-3) x 10(10) s(-1). The effects of introduction of a cyclopropane ring into a fatty acid upon the regiochemistry of hydroxylation are discussed.