Artificial Copper Enzymes for Asymmetric Diels-Alder Reactions

Chemical Society Reviews, 2005

Enantioselective catalysis is one of the most efficient ways to synthesize high-added-value enantiomerically pure organic compounds. As the subtle details which govern enantioselection cannot be reliably predicted or computed, catalysis relies more and more on a combinatorial approach. Biocatalysis offers an attractive, and often complementary, alternative for the synthesis of enantiopure products. From a combinatorial perspective, the potential of directed evolution techniques in optimizing an enzyme's selectivity is unrivaled. In this review, attention is focused on the construction of artificial metalloenzymes for enantioselective catalytic applications. Such systems are shown to combine properties of both homogeneous and enzymatic kingdoms. This review also includes our recent research results and implications in the development of new semisynthetic metalloproteins for the enantioselective hydrogenation of N-protected dehydroamino acids.

Angewandte Chemie, 2005

Catalysis offers efficient means to produce enantiopure products. Traditionally, enzymatic and homogeneous catalysis have evolved independently to afford mild, robust, active, and highly selective catalysts. Both systems are often considered complementary in terms of substrate and reaction scope, operating conditions, enantioselectivity mechanism, reaction medium, etc. For the optimization of activity and selectivity, directed-evolution methodologies (combined with an efficient selection or screening tool) outperform combinatorial ligand libraries. With the hope of alleviating some of the inherent limitations of both enzymatic and organometallic catalysis, two approaches have recently witnessed a revival: 1) organocatalysis and 2) artificial metalloenzymes based on either covalent or supramolecular anchoring of a catalytic moiety in a macromolecular host. Inspired by the early works of Whitesides and Wilson, we recently reported artificial metalloenzymes based on the biotin-avidin technology. Herein, we report our efforts to produce substrate-specific and S-selective artificial metalloenzymes based on the biotin-avidin technology for the hydrogenation of a-acetamidodehydroamino acids. The starting point for the chemogenetic-optimization procedure presented herein is the identification of [Rh(cod)-(biot-1)] + &S112G Sav (cod = 1,5-cyclooctadiene, biot = [*] Dr.

2016

Studies and development of artificial metalloenzymes have developed into vibrant areas of research. It is expected that artificial metalloenzymes will be able to combine the best of enzymatic and homogenous catalysis, that is, a broad catalytic scope, high selectivity and activity under mild, aqueous conditions. Artificial metalloenzyme consist of a host protein and a newly introduced artificial metal center. The host protein merely functions as ligand controlling selectivity and augmenting reactivity, while the metal center determines the reactivity. Potential applications range from catalytic production of fine chemicals and feedstock to electron transfer utilization (e.g. fuel cells, water splitting) and medical research (e.g. metabolic screening). Particularly modern asymmetric synthesis is expected to benefit from a successful combination of the power of biocatalysis (substrate conversion via multi-step or cascade reactions, potentially immortal catalyst, unparalleled selectivity and optimization by evolutionary methods) with the versatility and mechanism based optimization methods of homogeneous catalysis. However, so far systems are either limited in structural diversity (biotin-avidin technology) or fail to deliver the selectivities expected (covalent approaches). This thesis explores a novel strategy based on the site-selective incorporation of unnatural, metal binding amino acids into a host protein. The unnatural amino acids can either serve directly as metal binding centers can be used as anchoring points for artificial metallo-cofactors. The identification expression, purification and modification of a suitable protein scaffolds

Johnson Matthey Technology Review, 2020

, before moving to the University of Cambridge to begin a PhD on the synthesis and reactivity of Lewis acidic, heterobimetallic main group compounds. Shortly after obtaining her PhD in 2005, she was appointed to a joint College Lectureship in the

Nature Catalysis, 2019

CHIMIA, 2003

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.

Nature, 2016

The field of biocatalysis has advanced from harnessing natural enzymes to using directed evolution to obtain new biocatalysts with tailor-made functions. Several tools have recently been developed to expand the natural enzymatic repertoire with abiotic reactions. For example, artificial metalloenzymes, which combine the versatile reaction scope of transition metals with the beneficial catalytic features of enzymes, offer an attractive means to engineer new reactions. Three complementary strategies exist: repurposing natural metalloenzymes for abiotic transformations; in silico metalloenzyme (re-)design; and incorporation of abiotic cofactors into proteins. The third strategy offers the opportunity to design a wide variety of artificial metalloenzymes for non-natural reactions. However, many metal cofactors are inhibited by cellular components and therefore require purification of the scaffold protein. This limits the throughput of genetic optimization schemes applied to artificial m...

Angewandte Chemie International Edition, 2021

Many natural metalloenzymes assemble from proteins and biosynthesised complexes, generating potent catalysts by changing metal coordination. Here we adopt the same strategy to generate artificial metalloenzymes (ArMs) using ligand exchange to unmask catalytic activity. By systematically testing RuII(η6‐arene)(bipyridine) complexes designed to facilitate the displacement of functionalised bipyridines, we develop a fast and robust procedure for generating new enzymes via ligand exchange in a protein that has not evolved to bind such a complex. The resulting metal cofactors form peptidic coordination bonds but also retain a non‐biological ligand. Tandem mass spectrometry and 19F NMR spectroscopy were used to characterise the organometallic cofactors and identify the protein‐derived ligands. By introduction of ruthenium cofactors into a 4‐helical bundle, transfer hydrogenation catalysts were generated that displayed a 35‐fold rate increase when compared to the respective small molecule ...

ACS Central Science

Artificial metalloenzymes result from anchoring a metal cofactor within a host protein. Such hybrid catalysts combine the selectivity and specificity of enzymes with the versatility of (abiotic) transition metals to catalyze new-to-nature reactions in an evolvable scaffold. With the aim of improving the localization of an arylsulfonamide-bearing iridium-pianostool catalyst within human carbonic anhydrase II (hCAII) for the enantioselective reduction of prochiral imines, we introduced a covalent linkage between the host and the guest. Herein, we show that a judiciously positioned cysteine residue reacts with a p-nitropicolinamide ligand bound to iridium to afford an additional sulfonamide covalent linkage. Three rounds of directed evolution, performed on the dually anchored cofactor, led to improved activity and selectivity for the enantioselective reduction of harmaline (up to 97% ee (R) and >350 turnovers on a preparative scale). To evaluate the substrate scope, the best hits of each generation were tested with eight substrates. X-ray analysis, carried out at various stages of the evolutionary trajectory, was used to scrutinize (i) the nature of the covalent linkage between the cofactor and the host as well as (ii) the remodeling of the substrate-binding pocket.

Applied Organometallic Chemistry, 2005

Homogeneous and enzymatic catalysis offer complementary means to generate enantiomerically pure compounds. For this reason, in a biomimetic spirit, efforts are currently under way in different groups to design artificial enzymes. Two complementary strategies are possible to incorporate active organometallic catalyst precursors into a protein environment. The first strategy utilizes covalent anchoring of the organometallic complexes into the protein environment. The second strategy relies on the use of non-covalent incorporation of the organometallic precursor into the protein. In this review, attention is focused on the use of semisynthetic enzymes to produce efficient enantioselective hybrid catalysts for a given reaction. This article also includes our recent research results and implications in developing the biotin-avidin technology to localize the biotinylated organometallic catalyst precursor within a well-defined protein environment.