Exploiting and Engineering Neuroglobin for Catalyzing Carbene N–H Insertions and the Formation of Quinoxalinones
Li-Juan Sun, Huamin Wang, Jiakun Xu, Shu‐Qin Gao, Ge‐Bo Wen, Ying‐Wu Lin
Abstract
It is desired to design and construct more efficient enzymes with better performance to catalyze carbene N–H insertions for the synthesis of bioactive molecules. To this end, we exploited and designed a series of human neuroglobin (Ngb) mutants. As shown in this study, a double mutant, A15C/H64G Ngb, with an additional disulfide bond and a modified heme active site, exhibited yields up to >99% and total turnover numbers up to 33000 in catalyzing the carbene N–H insertions for aromatic amine derivatives, including those with a large size such as 1-aminopyrene. Moreover, for o -phenylenediamine derivatives, they underwent two cycles of N–H insertions, followed by cyclization to form quinoxalinones, as confirmed by the X-ray crystal structures. This study suggests that Ngb can be designed into a functional carbene transferase for efficiently catalyzing carbene N–H insertion reactions with a range of substrates. It also represents the first example of the formation of quinoxalinones catalyzed by an engineered heme enzyme.