Stereoselective Enzymatic Synthesis of Heteroatom-Substituted Cyclopropanes

The repurposing of hemoproteins for non-natural carbene transfer activities has generated enzymes for functions previously accessible only to chemical catalysts. With activities constrained to specific substrate classes, however, the synthetic utility of these new biocatalysts has been limited. To expand the capabilities of non-natural carbene transfer biocatalysis, we engineered variants of Cytochrome P450BM3 that catalyze the cyclopropanation of heteroatom-bearing alkenes, providing valuable nitrogen-, oxygen-, and sulfur-substituted cyclopropanes. Four or five active-site mutations converted a single parent enzyme into selective catalysts for the synthesis of both cis and trans heteroatom-substituted cyclopropanes, with high diastereoselectivities and enantioselectivities and up to 40 000 total turnovers. This work highlights the ease of tuning hemoproteins by directed evolution for efficient cyclopropanation of new substrate classes and expands the catalytic functions of iron heme proteins.