Flavinium Catalysed Photooxidation: Detection and Characterization of Elusive Peroxyflavinium Intermediates

Zelenka, Jan; Cibulka, Radek; Roithová, Jana

doi:10.1002/anie.201906293

Cited by 32 publications

(28 citation statements)

References 77 publications

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“…The original Dakin method uses an excess of hydrogen peroxide and sodium hydroxide at elevated temperatures. Interestingly, flavin also catalyzes Dakin oxidation of aromatic aldehydes in the presence of oxygen or hydrogen peroxide as sacrificial oxidants under mild conditions …”

Section: Resultsmentioning

confidence: 99%

Photochemistry of a 9‐Dithianyl‐Pyronin Derivative: A Cornucopia of Reaction Intermediates Lead to Common Photoproducts

et al. 2020

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Leaving groups attached to the meso‐methyl position of many common dyes, such as xanthene, BODIPY, or pyronin derivatives, can be liberated upon irradiation with visible light. However, the course of phototransformations of such photoactivatable systems can be quite complex and the identification of reaction intermediates or even products is often neglected. This paper exemplifies the photochemistry of a 9‐dithianyl‐pyronin derivative, which undergoes an oxidative transformation at the meso‐position to give a 3,6‐diamino‐9H‐xanthen‐9‐one derivative, formic acid, and carbon monoxide as the main photoproducts. The course of this multi‐photon multi‐step reaction was studied under various conditions by steady‐state and time‐resolved optical spectroscopy, mass spectrometry and NMR spectroscopy to understand the effects of solvents and molecular oxygen on individual steps. Our analyses have revealed the existence of many intermediates and their interrelationships to provide a complete picture of the transformation, which can bring new inputs to a rational design of new photoactivatable pyronin or xanthene derivatives.

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Section: Resultsmentioning

confidence: 99%

Photochemistry of a 9‐Dithianyl‐Pyronin Derivative: A Cornucopia of Reaction Intermediates Lead to Common Photoproducts

et al. 2020

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“…A detailed subsequent spectroscopic study revealed that contrary to the reactions in the dark, covalent hydroperoxide binding occurs at the C4a-position with formation of 13 when conducting the reactions with catalyst 11 photochemically (Scheme 12). 22 This observation was rationalized based on a N5blocking effect after initial proton-coupled electron transfer (PCET), which results in N5-protonation. Flavins which contain a substituent in the N1-position, but are not substituted in the N10-position formally belong to the class of alloxazines.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Molecular Editing of Flavins for Catalysis

Rehpenn¹,

Walter²,

Storch³

2021

Synthesis

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The diverse activity of flavoenzymes in organic transformations has fascinated researchers for a long time. However, when applied outside an enzyme environment, the isolated flavin cofactor only shows largely reduced activity. This highlights the importance of embedding the reactive flavin’s isoalloxazine core in defined surroundings. The latter include crucial non-covalent interactions with amino acid side chains or backbone as well as controlled access to reactants such as molecular oxygen. Nevertheless, molecular flavins are increasingly applied in the organic laboratory as valuable organocatalysts. Chemical modification of the parent isoalloxazine structure is of particular interest in this context in order to achieve reactivity and selectivity in transformations, which are so far only known with flavoenzymes or even unprecedented. This review aims to give a systematic overview of the reported designed flavin catalysts and highlights the impact of each structural alteration. It is intended to serve as a source of information when comparing the performance of known catalysts, but also when designing new flavins. Over the last decades, molecular flavin catalysis has emerged from proof-of-concept reactions to increasingly sophisticated transformations. This stimulates anticipating new flavin catalyst designs for solving contemporary challenges in organic synthesis.

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“…The important role of ion pairing extends in fields like catalysis [5], organic synthesis [6][7][8], and the chemistry of flavonoids [9,10] and radical-induced DNA-strand breaks [11]. These charge-separated reaction intermediates are role of ion pairing extends in fields like catalysis [5], organic synthesis [6][7][8], and the chemistry of flavonoids [9,10] and radical-induced DNA-strand breaks [11]. These charge-separated reaction intermediates are often decisive for the character and efficiency of the follow-up reactions and product formation.…”

Section: Introductionmentioning

confidence: 99%

Topological Dynamics of a Radical Ion Pair: Experimental and Computational Assessment at the Relevant Nanosecond Timescale

2020

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Chemical processes mostly happen in fluid environments where reaction partners encounter via diffusion. The bimolecular encounters take place at a nanosecond time scale. The chemical environment (e.g., solvent molecules, (counter)ions) has a decisive influence on the reactivity as it determines the contact time between two molecules and affects the energetics. For understanding reactivity at an atomic level and at the appropriate dynamic time scale, it is crucial to combine matching experimental and theoretical data. Here, we have utilized all-atom molecular-dynamics simulations for accessing the key time scale (nanoseconds) using a QM/MM-Hamiltonian. Ion pairs consisting of a radical ion and its counterion are ideal systems to assess the theoretical predictions because they reflect dynamics at an appropriate time scale when studied by temperature-dependent EPR spectroscopy. We have investigated a diketone radical anion with its tetra-ethylammonium counterion. We have established a funnel-like transition path connecting two (equivalent) complexation sites. The agreement between the molecular-dynamics simulation and the experimental data presents a new paradigm for ion–ion interactions. This study exemplarily demonstrates the impact of the molecular environment on the topological states of reaction intermediates and how these states can be consistently elucidated through the combination of theory and experiment. We anticipate that our findings will contribute to the prediction of bimolecular transformations in the condensed phase with relevance to chemical synthesis, polymers, and biological activity.

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Flavinium Catalysed Photooxidation: Detection and Characterization of Elusive Peroxyflavinium Intermediates

Cited by 32 publications

References 77 publications

Photochemistry of a 9‐Dithianyl‐Pyronin Derivative: A Cornucopia of Reaction Intermediates Lead to Common Photoproducts

Photochemistry of a 9‐Dithianyl‐Pyronin Derivative: A Cornucopia of Reaction Intermediates Lead to Common Photoproducts

Molecular Editing of Flavins for Catalysis

Topological Dynamics of a Radical Ion Pair: Experimental and Computational Assessment at the Relevant Nanosecond Timescale

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