Exploiting nature’s catalysts for non-natural transformations that are inaccessible to chemocatalysis is highly desirable but challenging. On the one hand, the widespread nicotinamide-dependent oxidoreductases have not been utilized for single-electron-transfer-induced bimolecular cross-couplings; on the other, the addition of catalytic asymmetric radical conjugate to terminal alkenes remains a challenge owing to strong racemic background reaction and unselective termination of prochiral radical species. Here we report a chemomimetic biocatalysitic approach for construction of alpha-carbonyl stereocentres via an unnatural intermolecular conjugate addition of N-(acyloxy)phthalimides-derived radicals with acceptor-substituted terminal alkenes, by combination of visible-light excitation and nicotinamide-dependent ketoreductases (KREDs). Based on protein crystal structure, we engineered KREDs via a semi-rational mutagenesis strategy to improve reaction outcomes with a small and high-quality variants library. Mechanistic investigations combining wet experiments, crystallographic studies and computational simulations demonstrate that the repurposed biocatalyst can suppress racemic background reaction and unselected side reactions, yielding enantioselectivity that is challenging to achieve by chemocatalysis.

利用自然界的催化剂进行化学催化无法实现的非天然转化是非常可取的，但也是具有挑战性的。一方面，广泛存在的烟酰胺依赖性氧化还原酶尚未用于单电子转移诱导的双分子交叉偶联；另一方面，由于强烈的外消旋背景反应和前手性自由基物种的非选择性终止，向末端烯烃添加催化不对称自由基共轭物仍然是一个挑战。在这里，我们报告了一种化学模拟生物催化方法，用于通过N的非自然分子间共轭加成来构建 α-羰基立体中心。-(酰氧基)邻苯二甲酰亚胺衍生自由基，具有受体取代的末端烯烃，通过可见光激发和烟酰胺依赖性酮还原酶 (KRED) 的组合。基于蛋白质晶体结构，我们通过半理性诱变策略设计了 KRED，以通过小型且高质量的变体库改善反应结果。结合湿实验、晶体学研究和计算模拟的机理研究表明，重新利用的生物催化剂可以抑制外消旋背景反应和未选择的副反应，产生化学催化难以实现的对映选择性。