Norcarane (1) and spiro[2.5]octane (2) yield different product distributions depending on whether they are oxidized via concerted, radical, or cationic mechanisms. For this reason, these two probes were used to investigate the mechanisms of hydrocarbon hydroxylation by two mammalian and two bacterial cytochrome P450 enzymes. Products indicative of a radical intermediate with a lifetime ranging from 16 to 52 ps were detected during the oxidation of norcarane by P450(cam) (CYP101), P450(BM3) (CYP102), CYP2B1, and CYP2E1. Trace amounts of the cation rearrangement product were observed with norcarane for all but CYP2E1, while no cation or radical rearrangement products were observed for spiro[2.5]octane. The results for the oxidation of norcarane with a radical rearrangement rate of 2 x 10(8) s(-1) are consistent with the involvement of a two-state radical rebound mechanism, while for the slower (5 x 10(7) s(-1)) spiro[2,5]oct-4-yl radical rearrangement products were beyond detection. Taken together with earlier data for the hydroxylation of bicyclo[2.1.0]pentane, which also suggested a 50 ps radical lifetime, these three structurally similar and functionally simple substrates show a consistent pattern of rearrangement that supports a radical rebound mechanism for this set of cytochrome P450 enzymes.

中文翻译：

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用自由基钟 Norcarane 和 Spiro[2,5] 辛烷重新审视 P450 酶的机制

Norcarane (1) 和螺 [2.5] 辛烷 (2) 产生不同的产物分布，这取决于它们是通过协同、自由基还是阳离子机制氧化。因此，这两种探针用于研究两种哺乳动物和两种细菌细胞色素 P450 酶的烃羟基化机制。在通过 P450(cam) (CYP101)、P450(BM3) (CYP102)、CYP2B1 和 CYP2E1 氧化去甲茛烷的过程中，检测到具有 16 到 52 ps 寿命的自由基中间体的产物。对于除 CYP2E1 以外的所有物质，用去甲烷观察到痕量的阳离子重排产物，而对于螺 [2.5] 辛烷没有观察到阳离子或自由基重排产物。自由基重排率为 2 x 10(8) s(-1) 的降卡烷氧化结果与二态自由基反弹机制的参与一致，而对于较慢的 (5 x 10(7) s (-1)) 螺[2,5] oct-4-yl 自由基重排产物无法检测。结合双环[2.1.0]戊烷羟基化的早期数据，这也表明自由基寿命为 50 ps，这三种结构相似且功能简单的底物显示出一致的重排模式，支持该组的自由基回弹机制细胞色素 P450 酶。