A Co(TAML)-Based Artificial Metalloenzyme for Asymmetric Radical-Type Oxygen Atom Transfer Catalysis

Generating artificial metalloenzymes (ArMs) by incorporating a non-natural metallocofactor within a protein host is an attractive strategy to complement homogeneous catalysts and enzymes. In an effort to achieve Co(TAML) catalyzed asymmetric radical-type oxygen atom transfer catalysis, we anchored a biotinylated Co(TAML) cofactor into streptavidin. In the presence of iodosylbenzene and α-methylstyrene, the Co(TAML) based ArM led to the corresponding enantioenriched oxirane, thereby expanding the scope of ArMs that facilitate radical-type transformations. Screening of the Sav library—that included (double) mutations at positions S112 and K121—enabled improvement of both the activity and the selectivity of the Co-TAML-catalyzed epoxidation reaction. Evaluation of the secondary coordination sphere around the Co(TAML) cofactor by analysis of the X-ray structures of two different ArMs: Co(TAML) · Sav WT and Co(TAML) · Sav S112Y, suggested how mutations may affect the catalytic properties.