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.