Synthesen in der Lumiflavinreihe IV

Hemmerich, P.; Prijs, B.; Erlenmeyer, H.

doi:10.1002/hlca.19590420522

Cited by 42 publications

(32 citation statements)

References 6 publications

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“…The lumiflavin 6c thus obtained was contaminated with 10% of its demethylation product lumichrome. The mixture was separated by preparative HPLC using 60% methanol, yielding 75% of pure lumiflavin 6c that was N(3)-methylated according to the procedure of Hemmerich et al 15 to yield 96% of lumiflavin lc (isotopic purity 98% as determined by mass spectrometry).…”

Section: -Hydroxyethylmentioning

confidence: 99%

¹H, ²H, ¹⁹F, ¹⁴N ENDOR and TRIPLE resonance investigations of substituted flavin radicals in their different protonation states

Weilbacher

Helle

Elsner

et al. 1988

Magnetic Reson in Chemistry

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A variety of isotopically labelled and/or substituted flavins have been converted into their corresponding radical states. Cation and neutral radicals were generated chemically and anion radicals were obtained electrochemically. By performing ENDOR and TRIPLE resonance experiments, complete sets of hyperfine coupling constants including their signs were accessible. The hyperfine data allowed (a) identification of the radical state present, (b) information to be obtained about the preferred conformational arrangements of the substituents and (c) conclusions to be drawn about the influences of the substituents on the spin density distributions of the different radical states. KEY WORDS ENDOR TRIPLE resonance spectroscopy Flavin radicals Electrochemical generation of radicals I N T R O D U C T I O NFlavins can occur in three different redox states analogous to the quinone redox system, viz. the quinoid, the semiquinoid, and the hydroquinoid form :Moreover, the three species can exist in different protonation states depending on the pH of the solution. A general rule states that flavoprotein oxidases form the anionic radical state while flavoprotein dehydrogenases and flavodoxins form the neutral radical state in high yields. Flavoprotein monooxygenases form few radicals or do not give semiquinones. Investigations of the flavin redox system and its ubiquitous biological function have been summarized in a variety of reviews; more recent reviews are those by Muller,' Edmondson and Tollin,' W a l~h ,~ Mobius and Lubitz4 and Kurreck et al. ' Michaelis and Schwarzenbach6 were the first to detect flavin radical species. This observation was confirmed by B e i~~e r t ,~ who published the first EPR spectra of flavin radicals. In the last two decades the radical states of flavoproteins and flavin model compounds have attracted increasing attention. Using frozen solutions of flavoproteins, the structure of the paramagnetic coenzyme in the free and protein-bound state and its protonation state could be evaluated from the application of the ENDOR t e c h n i q~e .~*~ In order to obtain

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Section: -Hydroxyethylmentioning

confidence: 99%

¹H, ²H, ¹⁹F, ¹⁴N ENDOR and TRIPLE resonance investigations of substituted flavin radicals in their different protonation states

Weilbacher

Helle

Elsner

et al. 1988

Magnetic Reson in Chemistry

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“…The reaction mixture became dark coloured and much insoluble material precipitated. This is due to the lability of the 8-methyl group of riboflavin in aprotic basic solvents [42]. Acetylation of 5'-FMN with acetic anhydride in pyridine was found to yield a crude mixture (cj: Fig.…”

Section: Acetylation Of Fmnmentioning

confidence: 99%

Synthesis, Separation, Identification and Interconversion of Riboflavin Phosphates and Their Acetyl Derivatives: A Reinvestigation

Scola-Nagelschneider

Hemmerich

1976

European Journal of Biochemistry

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A reinvestigation of flavin phosphate synthesis, separation, identification, and interconversion was made in view of contradictory results in the literature. It has been confirmed that monochlorophosphoric acid is the best agent for selective 5′‐monophosphorylation of riboflavin and derivatives. This reaction yields, however, invariably up to 20% of an isomer, which has been separated by preparative thick‐layer chromatography and shown to be the 4′‐monophosphate. All the earlier authors failed to detect this isomer which does not bind to flavodoxin. It equilibrates in dilute mineral acid to yield an 8:2 mixture of 5′‐phosphate to 4′‐phosphate by phosphate migration. The formation of 2′,3′,4′‐triacetyl‐flavin mononucleotide, according to Christie, S. M. H., Kenner, G. W. & Todd, A. R. (1954) J. Chem. Soc., 46–52, upon acid‐catalysed acetylation of pure FMN, was confirmed. The same reaction under base catalysis, however, does not yield 2′,3′,4′‐triacetyl‐flavin mononucleotide as claimed by Khomutova, E. D., Shapiro, T. A., Mezentseva, M. V. & Berezovskii, V. M. (1965) Otd. Ohshch. i Tekhn. Khim., 241–244, Chem. Absir. 65, 5516a, but in fact up to 80% 2′,3′‐diacetyl‐flavin 4′: 5′‐cyclophosphate as the main product, which is stable under neutral and weak acidic conditions and does not hydrolyse to 2′,3′‐diacetyl‐flavin 5′‐monophosphate as claimed by McCormick, D. B. (1974) J. Heterocycl. Chem. 11, 969–974. The various flavin phosphates and their acetyl derivatives have been identified by pH‐titration, electrophoresis, and proton magnetic resonance spectrometry, which permit direct analyses of crude reaction products as well as a rapid purity check of commercial FMN.

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“…Such cyclic hemiacetals can be trapped in the acid photolysis of 10-(hydroxyalky1)-flavins, e.g. riboflavin or flavocoenzymes, in a sequence of 10-side-chain dehydrogenation and N ( 1)-cycloaminal cation formation of the lob-carbonyl formed, which results in a quenching of the further photolysis in favor of 9-photoaddition.Since the discovery of covalent 8a-dimerization of riboflavin and its derivatives [3], evidence has been accumulating with respect to the reactivity of the benzenoid subnucleus of flavoquinone (Fl0,H) Abbreviations. EPR, electron paramagnetic resonance ; NMR, nuclear magnetic resonance; INDOR, inter-nuclear double resonance ; Me,SO, dimethylsulfoxide.…”

mentioning

confidence: 99%

“…Since the discovery of covalent 8a-dimerization of riboflavin and its derivatives [3], evidence has been accumulating with respect to the reactivity of the benzenoid subnucleus of flavoquinone (Fl0,H) Abbreviations. EPR, electron paramagnetic resonance ; NMR, nuclear magnetic resonance; INDOR, inter-nuclear double resonance ; Me,SO, dimethylsulfoxide.…”

mentioning

confidence: 99%

Nucleophilic Addition at the Photoexcited Flavin Cation: Synthesis and Properties of 6- and 9-Hydroxy-Flavocoenzyme Chromophores

Schöllnhammer¹,

Hemmerich²

1974

Eur J Biochem

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1. The method of "photohydroxylation" of azaheteroaromatics, known in the phenazine and alloxazine series, has been applied to flavin ( = isoalloxazine) derivatives FbxH. The products habe been identified as 6-and 9-hydroxyflavins (FlOx-6/9-OH). On this basis it was possible to assign a 6-hydroxyflavin structure to the new flavocoenzyme chromophores described by Mayhew et al. in the accompanying paper.2. I n agreement with the data obtained by Dekker et al. in a recent laser study on alloxazine, we find that the reaction proceeds via addition of water, alcohols or carboxylic acids by the lowest excited singlet state of flavin with synchronous intramolecular hydrogen shift from the site of RO-addition [= C(6) or C(9)l towards N(5) and subsequent oxidation of the 6/9-hydroxy-1 $-dihydroflavin formed.3. The photoaddition reaction occurs in competition with photodehydrogenation of available CH-bonds by the lowest excited flavin triplet, in which case the CH-substrate may be provided by the solvent ROH or, when R = H, by methyl groups of a second flavin molecule (= flavin autophotolysis). This photodehydrogenation may be suppressed by 0,-dependent triplet quenching and/or by applying a positive charge to the flavin (RFl,,H+, R = H or alkyl) in order to inhibit the reaction with itself.4. Differentiation of 6-and 9-hydroxyflavin isomers was possible by double resonance evaluation of the proton coupling between the residual Ar-H and the adjacent methyl group, by evaluation of the electron paramagnetic resonance hyperhe coupling for the residual Ar-H in the radical cations 1 ,5-RHlk6/9-OH, and by formation of cupric chelates from 6-hydroxy-flavin as compared to the lack of metal affinity in the 9-isomer. lH-Nuclear magnetic resonance, electron paramagnetic resonance and visible spectra and their dependence on the state of ionisation of hydroxyflavins are discussed. Hydroxyflavin anions as well as their N( 1)-alkylated meso-ionic derivatives are shown to exhibit characteristic long-wavelength absorption bands ranging from 50 to 800 nm with maxima around 600 nm and low molar absorption coefficients between 500 and 3000 M-bm-l (as compared to =lo4 for the first n, n* transition a t %400 nm), which might be readily mistaken for "flavin-substrate charge transfer'' bands. 5. 9-Methoxy-flavins could be spectroscopically related to 9 : 10-bridged cyclic hemiacetals obtained upon ring closure of 9-hydroxy groups with lob-carbonyl functions. Such cyclic hemiacetals can be trapped in the acid photolysis of 10-(hydroxyalky1)-flavins, e.g. riboflavin or flavocoenzymes, in a sequence of 10-side-chain dehydrogenation and N ( 1)-cycloaminal cation formation of the lob-carbonyl formed, which results in a quenching of the further photolysis in favor of 9-photoaddition.Since the discovery of covalent 8a-dimerization of riboflavin and its derivatives [3], evidence has been accumulating with respect to the reactivity of the benzenoid subnucleus of flavoquinone (Fl0,H) Abbreviations. EPR, electron paramagnetic resonance ; NMR, nuclear magnet...

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Synthesen in der Lumiflavinreihe IV

Cited by 42 publications

References 6 publications

¹H, ²H, ¹⁹F, ¹⁴N ENDOR and TRIPLE resonance investigations of substituted flavin radicals in their different protonation states

¹H, ²H, ¹⁹F, ¹⁴N ENDOR and TRIPLE resonance investigations of substituted flavin radicals in their different protonation states

Synthesis, Separation, Identification and Interconversion of Riboflavin Phosphates and Their Acetyl Derivatives: A Reinvestigation

Nucleophilic Addition at the Photoexcited Flavin Cation: Synthesis and Properties of 6- and 9-Hydroxy-Flavocoenzyme Chromophores

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Synthesen in der Lumiflavinreihe IV

Cited by 42 publications

References 6 publications

1H, 2H, 19F, 14N ENDOR and TRIPLE resonance investigations of substituted flavin radicals in their different protonation states

1H, 2H, 19F, 14N ENDOR and TRIPLE resonance investigations of substituted flavin radicals in their different protonation states

Synthesis, Separation, Identification and Interconversion of Riboflavin Phosphates and Their Acetyl Derivatives: A Reinvestigation

Nucleophilic Addition at the Photoexcited Flavin Cation: Synthesis and Properties of 6- and 9-Hydroxy-Flavocoenzyme Chromophores

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¹H, ²H, ¹⁹F, ¹⁴N ENDOR and TRIPLE resonance investigations of substituted flavin radicals in their different protonation states

¹H, ²H, ¹⁹F, ¹⁴N ENDOR and TRIPLE resonance investigations of substituted flavin radicals in their different protonation states