A designed photoenzyme for enantioselective [2+2] cycloadditions

Abstract

The ability to programme new modes of catalysis into proteins would allow the development of enzyme families with functions beyond those found in nature. To this end, genetic code expansion methodology holds particular promise, as it allows the site-selective introduction of new functional elements into proteins as non-canonical amino acid side chains. [1][2][3][4] Here, we exploit an expanded genetic code to develop a photoenzyme that operates via triplet energy transfer catalysis, a versatile mode of reactivity in organic synthesis that is currently not accessible to biocatalysis. [5][6][7][8][9][10][11][12] Installation of a genetically encoded photosensitiser into the beta-propeller scaffold of DA_20_00 13 converts a de novo Diels-Alderase into a photoenzyme for [2+2]cycloadditions (EnT1.0). Subsequent development and implementation of a platform for photoenzyme evolution afforded an efficient and enantioselective enzyme (EnT1.3, up to 99% e.e.) that can promote selective cycloadditions that have proven challenging to achieve with small molecule catalysts. EnT1.3 performs >300 turnovers and, in contrast to small molecule photocatalysts, can operate effectively under aerobic conditions. A 1.7 Å resolution X-ray crystal structure of an EnT1.3-product complex shows how multiple functional components work in synergy to promote efficient and selective photocatalysis. This study opens the door to a wealth of new excited-state chemistry in protein active sites and establishes the framework for developing a new generation of evolvable photocatalysts with efficiencies and specificities akin to natural enzymes.

Photovoltaic enzymes by design and evolution

“…Our proof-of-concept work provides a valuable addition to the growing interest in accessing novel reactivities through the creation and evolution of photoenzymes. 35,36 In particular, EOY can give rise to a diverse range of photochemistries 29 that could be exploited in the future. We have demonstrated a methodological framework for enzyme photosensitization by design and evolution, which could potentially be used to create highly efficient photo-biocatalysts for various societal critical reactions.…”

Iridium(III) Polypyridine Artificial Metalloenzymes with Tunable Photophysical Properties: a New Platform for Visible Light Photocatalysis in Aqueous Solution

“…5,6 Very recently, two groups independently established that a benzophenone photosensitizer could be genetically encoded into different protein scaffolds to enable similar reactions with high selectivity imposed by second sphere interactions. 7,8 Based on these precedents, we hypothesized that a protein scaffold could be used to control the photophysical and catalytic properties of robust Ir(III) polypyridyl photocatalysts in analogy to reports using other protein-encapsulated chromophores. [9][10][11][12] We recently established that artificial metalloenzyme (ArM) photocatalysts could be constructed by covalently linking tris-bipyridine Ru(II) complexes within the large active site of a prolyl oligopeptidase (POP) from Pyrococcus furiosus.…”

“…The observed yields, diastereoselectivities, and rates (Figure S9) were similar to those obtained for the cofactors alone, however, suggesting that substrate scaffold interactions are insufficient to impart selectivity. 6) and 4-methoxy styrene (7). (b) Intramolecular [2+2] photocycloaddition of 3-(3-buten-1-yloxy)-2(1H)quinolinone (9).…”

Photoexcited Enzymes for Asymmetric Csp3−Csp3 Cross‐Electrophile Couplings

“… a) Several strategies have been devised in the past to develop enzymes that catalyze novel reaction types. b) Emerging concepts comprising the combination of photochemistry and enzyme catalysis to induce abiological reaction chemistries in enzymes [10–13] . c) Photoenzymatic asymmetric cross‐electrophile coupling (XEC) developed by Hyster and co‐workers [15] .…”