2 publications

2 publications

Abiotic reduction of ketones with silanes catalysed by carbonic anhydrase through an enzymatic zinc hydride

Hartwig, J.F.

Nat. Chem. 2021, 13, 312-318, 10.1038/s41557-020-00633-7

Enzymatic reactions through mononuclear metal hydrides are unknown in nature, despite the prevalence of such intermediates in the reactions of synthetic transition-metal catalysts. If metalloenzymes could react through abiotic intermediates like these, then the scope of enzyme-catalysed reactions would expand. Here we show that zinc-containing carbonic anhydrase enzymes catalyse hydride transfers from silanes to ketones with high enantioselectivity. We report mechanistic data providing strong evidence that the process involves a mononuclear zinc hydride. This work shows that abiotic silanes can act as reducing equivalents in an enzyme-catalysed process and that monomeric hydrides of electropositive metals, which are typically unstable in protic environments, can be catalytic intermediates in enzymatic processes. Overall, this work bridges a gap between the types of transformation in molecular catalysis and biocatalysis.


Metal: Zn
Ligand type: Histidine residues
Anchoring strategy: Native
Optimization: Chemical
Max TON: 500
ee: >99
PDB: ---
Notes: ---

Noncanonical Heme Ligands Steer Carbene Transfer Reactivity in an Artificial Metalloenzyme

Hilvert, D.

Angew. Chem. Int. Ed. 2021, 60, 15063-15068, 10.1002/anie.202103437

Changing the primary metal coordination sphere is a powerful strategy for tuning metalloprotein properties. Here we used amber stop codon suppression with engineered pyrrolysyl-tRNA synthetases, including two newly evolved enzymes, to replace the proximal histidine in myoglobin with Nδ-methylhistidine, 5-thiazoylalanine, 4-thiazoylalanine and 3-(3-thienyl)alanine. In addition to tuning the heme redox potential over a >200 mV range, these noncanonical ligands modulate the protein's carbene transfer activity with ethyl diazoacetate. Variants with increased reduction potential proved superior for cyclopropanation and N–H insertion, whereas variants with reduced Eo values gave higher S–H insertion activity. Given the functional importance of histidine in many enzymes, these genetically encoded analogues could be valuable tools for probing mechanism and enabling new chemistries.


Metal: Fe
Ligand type: Histidine residues
Host protein: Myoglobin (Mb)
Anchoring strategy: Heme
Optimization: Genetic
Reaction: Cyclopropanation
Max TON: ---
ee: >99
PDB: ---
Notes: yield: styrene cyclopropanation 71% max, cf free heme <5%

Metal: Fe
Ligand type: Histidine residues
Host protein: Myoglobin (Mb)
Anchoring strategy: Heme
Optimization: Genetic
Reaction: N-H Insertion
Max TON: ---
ee: ---
PDB: ---
Notes: Yield: aniline insertion 74-93%

Metal: Fe
Ligand type: Histidine residues
Host protein: Myoglobin (Mb)
Anchoring strategy: Heme
Optimization: Genetic
Reaction: S-H insertion
Max TON: ---
ee: ---
PDB: ---
Notes: Yield: thiophenol insertion 18-36% but still outperforms heme