- Thiourea-enhanced flavin photooxidation of benzyl alcohol
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Upon irradiation, flavin oxidises 4-methoxybenzyl alcohol to the corresponding aldehyde using aerial O2 as the terminal oxidant. We have observed that this reaction is significantly accelerated by the presence of thiourea. A series of thiourea-functionalised flavins has been prepared from flavin isothiocyanates and their photocatalytic efficiencies have been monitored by NMR. The alcohol photooxidation proceeds rapidly and cleanly with high turnover numbers of up to 580, exceeding previously reported performances. A likely mechanistic rationale for the more than 30-fold acceleration of the photo-redox reaction by thiourea has been derived from spectroscopic, electrochemical, and kinetic studies. Thus, thiourea acts as an electron-transfer mediator for the initial photooxidation of 4-methoxybenzyl alcohol by the excited flavins. This mechanism has similarities to electron-relay mechanisms in flavoenzymes, for which cysteine sulfenic acid intermediates are proposed. The observation that thiourea mediates flavin photo-redox processes is valuable for the design of more sophisticated photocatalysts based on Nature's best redox chromophore.
- Svoboda, Jiri,Schmaderer, Harald,Koenig, Burkhard
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supporting information; scheme or table
p. 1854 - 1865
(2009/04/06)
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- Efficient syntheses of a flavin and an 8-hydroxy-5-deazaflavin amino acid and their incorporation into oligopeptides
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We report a convenient synthesis for the cofactor amino acids (S)-3 and (S)-4 in which the C5-ribose chain of the original riboflavin and ribo-5- deazaflavin cofactors is replaced by a C5-amino acid side chain. Both cofactor amino acids are available in enantiomerically pure form in gram quantities and can be incorporated into oligopeptides using a standard Fmoc- based solid-phase peptide synthesis protocol. The benzyl-protecting group of the 8-hydroxy-5-deazaflavin can be cleaved by hydrogenolysis directly on the peptide. This allows the investigation of the properties of the peptide bound redox active OH- and the deprotonated O- form of the deazaflavin. Due to the electron- and energy-transfer properties of both cofactors, applications of both amino acid in the preparation of peptide- and protein-based biosensors, of catalytically active peptides, or as chemical rulers for distance measurements in biopolymers based on the fluorescence resonance energy- transfer technology can be envisaged.
- Carell, Thomas,Schmid, Holger,Reinhard, Markus
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p. 8741 - 8747
(2007/10/03)
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- Towards artificial DNA-repair enzymes: Incorporation of a flavin amino acid into DNA-binding oligopeptides
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Mimicking DNA photolyases: Model proteins containing the flavin amino acid L-1 within the DNA-binding domain of a transcription factor are capable of completely repairing damage from the formation of pyrimidine dimers in single-stranded oligonucleotides.
- Carell,Butenandt
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p. 1461 - 1464
(2007/10/03)
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