Marchetti, M.

Adv. Synth. Catal. 2002, 344, 556, 10.1002/1615-4169(200207)344:5<556::AID-ADSC556>3.0.CO;2-E

The water‐soluble complex derived from Rh(CO)2(acac) and human serum albumin (HSA) proved to be efficient in the hydroformylation of several olefin substrates. The chemoselectivity and regioselectivity were generally higher than those obtained by using the classic catalytic systems like TPPTS‐Rh(I) (TPPTS=triphenylphosphine‐3,3′,3″‐trisulfonic acid trisodium salt). Styrene and 1‐octene, for instance, were converted in almost quantitative yields into the corresponding oxo‐aldehydes at 60 °C and 70 atm (CO/H2=1) even at very low Rh(CO)2(acac)/HSA catalyst concentrations. The possibility of easily recovering the Rh(I) compound makes the system environmentally friendly. The circular dichroism technique was useful for demonstrating the Rh(I) binding to the protein and to give information on the stability in solution of the catalytic system. Some other proteins have been used to replace HSA as complexing agent for Rh(I). The results were less impressive than those obtained using HSA and their complexes with Rh(I) were much less stable.

Bäckvall, J.E.; Diéguez, M.; Pàmies, O.

Adv. Synth. Catal. 2015, 357, 1567-1586, 10.1002/adsc.201500290

Artificial metalloenzymes combine the excellent selective recognition/binding properties of enzymes with transition metal catalysts, and therefore many asymmetric transformations can benefit from these entities. The search for new successful strategies in the construction of metal‐enzyme hybrid catalysts has therefore become a very active area of research. This review discusses all the developed strategies and the latest advances in the synthesis and application in asymmetric catalysis of artificial metalloenzymes with future directions for their design, synthesis and application (Sections 2–4). Finally, advice is presented (to the non‐specialist) on how to prepare and use artificial metalloenzymes (Section 5).

Filice, M.; Palomo, J.M.

Adv. Synth. Catal. 2015, 357, 2687-2696, 10.1002/adsc.201500014

A p‐nitrophenylphosphonate palladium pincer was synthesized and selectively inserted by irreversible attachment on the catalytic serine of different commercial lipases with good to excellent yields in most cases. Among all, lipase from Candida antarctica B (CAL‐B) was the best modified enzyme. The artificial metalloenzyme CAL‐B‐palladium (Pd) catalyst was subsequently immobilized on different supports and by different orienting strategies. The catalytic properties of the immobilized hybrid catalysts were then evaluated in two sets of Heck cross‐coupling reactions under different conditions. In the first reaction between iodobenzene and ethyl acrylate, the covalent immobilized CAL‐B‐Pd catalyst resulted to be the best one exhibiting quantitative production of the Heck product at 70 °C in dimethylformamide (DMF) with 25% water and particularly in pure DMF, where the soluble Pd pincer was completely inactive. A post‐immobilization engineering of catalyst surface by its hydrophobization enhanced the activity. The selectivity properties of the best hybrid catalyst were then assessed in the asymmetric Heck cross‐coupling reaction between iodobenzene and 2,3‐dihydrofuran retrieving excellent results in terms of stereo‐ and enantioselectivity.

Ward, T.R.

Adv. Synth. Catal. 2007, 349, 1923-1930, 10.1002/adsc.200700022

We report on our efforts to create efficient artificial metalloenzymes for the enantioselective hydrogenation of N‐protected dehydroamino acids using either avidin or streptavidin as host proteins. Introduction of chiral amino acid spacers – phenylalanine or proline – between the biotin anchor and the flexible aminodiphosphine moiety 1, combined with saturation mutagenesis at position S112X of streptavidin, affords second generation artificial hydrogenases displaying improved organic solvent tolerance, reaction rates (3‐fold) and (S)‐selectivities (up to 95 % ee for N‐acetamidoalanine and N‐acetamidophenylalanine). It is shown that these artificial metalloenzymes follow Michaelis–Menten kinetics with an increased affinity for the substrate and a higher kcat than the protein‐free catalyst (compare kcat 3.06 min−1 and KM 7.38 mM for [Rh(COD)Biot‐1]+ with kcat 12.30 min−1 and KM 4.36 mM for [Rh(COD)Biot‐(R)‐Pro‐1]+ ⊂ WT Sav). Finally, we present a straightforward protocol using Biotin‐Sepharose to immobilize artificial metalloenzymes (>92 % ee for N‐acetamidoalanine and N‐acetamidophenylalanine using [Rh(COD)Biot‐(R)‐Pro‐1]+ ⊂ Sav S112W).