Christophe Letondor

X‐Ray Structure and Designed Evolution of an Artificial Transfer Hydrogenase

A structure is worth a thousand words: guided by the crystal structure of an S-selective artificial transfer hydrogenase, designed evolution was used to optimize the selectivity of hybrid catalysts. Fine-tuning of the second coordination sphere of the ruthenium center by introduction of two point mutations allowed the identification of selective artificial transfer hydrogenases for the redn. of dialkyl ketones.

Artificial metalloenzymes for enantioselective catalysis : recent advances

Creating new catalytic function in proteins. Anchoring an organometallic moiety within a protein affords artificial metalloenzymes for enantioselective catalysis. Both chemical and genetic tools can be applied in the optimization of such systems, which lie at the interface between homogeneous and enzymatic catalysis. This minireview presents the latest developments in the field of artificial metalloenzymes.

Synthesis, structure, and complexation properties of partially and completely reduced meso-octamethylporphyrinogens (calix[4]pyrroles).

New tricks for an old dog: Calixpyrroles bind anions efficiently and can be transformed into transition-metal complexes only under forcing conditions. Reducing the macrocycle creates a ligand that easily forms classical Werner complexes with copper, nickel, and palladium ions. The metal complexes present an array of four directed hydrogen bonds, which specifically bind the counterions (see picture; blue N, white H, green Cl, red Cu, Ni, or Pd).

Catalytic hydrogenation of meso-octamethylporphyrinogen (calix[4]pyrrole).

Hydrogenation of meso-octamethylporphyrinogen (calix[4]pyrrole) with a number of heterogeneous catalysts under different experimental conditions has been investigated. GC-MS analyses of the reaction mixtures showed the formation of one to four products in low to moderate yields: three of them were diastereoisomers of the product derived from half-hydrogenation of the substrate, and displayed alternating pyrrolidine and pyrrole rings, while the fourth was the all-cis saturated product. An acidic medium was necessary to achieve hydrogenation. However, the use of too strongly acidic solvents or additives was detrimental to the stability of the substrate and/or the catalyst.

Exploiting the second coordination sphere: Proteins as host for enantioselective catalysis

With the aim of exploring the role of the second coordination sphere in enantioselective catalysis, achiral organometallic catalyst precursors are anchored in proteins via non-covalent interactions. A chemogenetic procedure allows the activity and the enantioselectivity of the artificial metalloenzymes to be optimized, to yield hybrid catalysts with features reminiscent both of enzymatic and homogeneous catalysts.