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Various metalloenzymes have been applied in laboratory-scale reactions and a few metalloenzymes such as nitrile hydratase (cobalt(III) in the active site) for the production of acrylamide have found application in industry .Notably, however, the reaction scope of natural enzymes is quite limited.The best studied and most commonly employed catalysts are based on Mo, W, and Ru .
This allyl group was modified with a GH-type catalyst and carbohydrate or small polyethylene glycol (PEG) groups were attached .
As another strategy to modify a protein surface with olefin metathesis, Isarov and Pokorski introduced a Grubbs 3rd generation catalyst on the surface of lysozyme and performed ring-opening metathesis polymerization (ROMP) on the protein surface employing a PEGylated norbornene derivative as substrate . These two examples illustrate the potential applications of olefin metathesis in protein modification.
The combination of an engineered protein with a synthetic metal catalyst leads to artificial metalloproteins [20-23].
In the case of a metathesis catalyst, so-called artificial metatheases are obtained, which could open new areas of biological applications .
Apart from engineering natural enzymes, the approach of connecting abiotic co-factors (such as organometallic complexes) to natural or re-engineered protein scaffolds offers an attractive combination of both, broad reaction scope of chemical transformations as well as control of selectivity and specificity as found in natural enzymes.
These so-called artificial metalloproteins or metalloenzymes offer two ways of fine-tuning activity and selectivity: As chemical means, the metal site can be adjusted and fine-tuned through modification of the ligands surrounding the metal.Keywords: Olefin metathesis constitutes the rearrangement of C=C double bonds in the presence of transition metal catalysts based on V, Mo, W, Re, Ru, and Os together with alkylating co-catalysts.This transformation is widely used in organic synthesis as well as in polymerization of various unsaturated monomers .As biotechnological means, the protein cavity acting as second coordination sphere can be optimized to tune specificity as well as stereo- and regioselectivity.The extensive literature of artificial metalloproteins has been summarized in various comprehensive reviews [20-22].In this short review, we focus on the status of embedding the GH-type catalyst into β-barrel proteins and show their application in various reactions using benchmark substrates.These transformations include all three fundamental olefin metathesis reactions: ring-opening metathesis polymerization (ROMP), ring-closing metathesis (RCM) as well as cross metathesis (CM) (Scheme 2).Further applications would be the implementation of olefin metathesis into natural metabolic pathways to allow synthesis of fine chemicals .Also, a targeted reaction in a certain environment within a living cell with a precise release or activation of the catalyst would enable new ways of drug delivery.According to the Chauvin mechanism, the catalytically active species are Schrock-type carbenes or alkylidenes .Olefin metathesis greatly profited from the isolation of structurally well-defined metal alkylidene complexes [3,4].