Since the discovery of Hofmann–Löffler–Freytag reaction more than 130 years ago, both the structure and reactivity of nitrogen-centred radicals have been widely studied. Nevertheless, catalytic enantioselective intermolecular radical hydroamination remains a challenge due to the existence of side reactions, the short lifetime of nitrogen-centred radicals and lack of understanding of the fundamental catalytic steps. In the laboratory, nitrogen-centred radicals are produced with radical initiators, photocatalysts or electrocatalysts. In contrast, their generation and reaction are unknown in nature. Here we report a pure biocatalytic system for the photoenzymatic production of nitrogen-centred radicals and enantioselective intermolecular radical hydroaminations by successfully repurposing an ene-reductase through directed evolution. These reactions progress efficiently at room temperature under visible light without any external photocatalysts and exhibit excellent enantioselectivities. A detailed mechanistic study reveals that the enantioselectivity originates from the radical-addition step while the reactivity originates from the ultrafast photoinduced electron transfer from reduced flavin mononucleotide to nitrogen-containing substrates.

自从 130 多年前发现 Hofmann-Löffler-Freytag 反应以来，以氮为中心的自由基的结构和反应性都得到了广泛的研究。然而，由于副反应的存在、以氮为中心的自由基的寿命短以及缺乏对基本催化步骤的了解，催化对映选择性分子间自由基氢胺化仍然是一个挑战。在实验室中，用自由基引发剂、光催化剂或电催化剂产生以氮为中心的自由基。相反，它们的产生和反应本质上是未知的。在这里，我们报告了一种纯生物催化系统，通过定向进化成功地重新利用烯还原酶，用于光酶法产生以氮为中心的自由基和对映选择性分子间自由基氢胺化。这些反应在室温下可见光下有效进行，无需任何外部光催化剂，并表现出优异的对映选择性。详细的机理研究表明，对映选择性源于自由基加成步骤，而反应性源于从还原黄素单核苷酸到含氮底物的超快光诱导电子转移。