Studies on Flavin Derivatives. Crystal Structure of 5-Acetyl-9-bromo-1,3,7,8-tetramethyl-1,5-dihydroalloxazine.

Leijonmarck, Marie; Werner, Per‐Erik; Seppälä, Ilkka J.; Hedberg, Kenneth; Schaumburg, Kjeld; Ehrenberg, L.

doi:10.3891/acta.chem.scand.25-2273

Cited by 12 publications

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“…Furthermore, substituents (alkylations) are generally found on the N 1 and most problematically on the N 5 position. [62][63][64][65] This makes these derivatives chemically distinct from the biologically relevant flavins FMN, FAD, and lumiflavin.…”

Section: Resultsmentioning

confidence: 99%

“…The fully reduced flavin however is bent about the N 5 −N 10 axis, although the exact amount of the butterfly bend angle is uncertain because different flavin derivatives show different bend angles. Furthermore, substituents (alkylations) are generally found on the N 1 and most problematically on the N 5 position. − This makes these derivatives chemically distinct from the biologically relevant flavins FMN, FAD, and lumiflavin.…”

Section: Resultsmentioning

confidence: 99%

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NMR Shieldings and Electron Correlation Reveal Remarkable Behavior on the Part of the Flavin N₅ Reactive Center

Walsh

Miller

2002

J. Phys. Chem. B

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NMR calculations on oxidized lumiflavin using density functional theory (DFT) reveal that methods including electron correlation show significant improvements in the flavin carbon and nitrogen NMR shieldings over uncorrelated Hartree−Fock (HF) results. In particular, the GIAO B3PW91//B3PW91 cc-pVTZ NMR shielding of the important N5 reactive center shows an improvement of 60.7 ppm over GIAO HF//B3PW91 cc-pVTZ, bringing it to within 6.1 ppm of the solvent-corrected experimental value. While the N5 center becomes dramatically shielded upon going from HF to correlated NMR shieldings, with the exception of C10a, all other NMR resonances are systematically deshielded. The nitrogens N1, N3, and N10 become deshielded by 23−26 ppm, and carbons become deshielded by an average of 5.2 ppm, bringing them into better agreement with experiment. Similar results are obtained with the significantly smaller 6-311G(d,p) basis set. The effects of electron correlation through the flavin geometry are also evident. The geometries calculated by B3LYP, B3PW91, and MP2 correlated methods using the 6-311G(d,p) basis lead to systematic NMR deshielding for all flavin heavy atoms in comparison with those obtained at the HF geometry. On average, the flavin nitrogens become deshielded by more than 10 ppm and carbons by almost 4 ppm. Similar changes, but of smaller magnitude, are observed for the NMR shieldings of fully reduced flavin, indicating that electron correlation is less important in that flavin state. The magnitude of the dramatic NMR shielding increase of several electrophilic centers upon flavin reduction is well captured by DFT methods. In particular, the GIAO B3PW91/cc-pVTZ N5 NMR shielding difference between oxidized and reduced flavin is 299.6 ppm, which compares well to the solvent-corrected experimental shielding difference of 299.1 ppm. The N5 center is also remarkable for its large decrease in shielding, by 33.4 ppm (98.0 ppm deshielding of σ11), upon protonation of the oxidized flavin at N1, a process which activates N5 for electrophilic attack.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

NMR Shieldings and Electron Correlation Reveal Remarkable Behavior on the Part of the Flavin N₅ Reactive Center

Walsh

Miller

2002

J. Phys. Chem. B

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“…We wish to emphasize that our calculations of the endocyclic angles of the N(5) and the N(10) atoms do not yield numerical values on the degree of folding of the reduced flavin molecule, although the endocyclic angles of the two atoms are related to the degree of folding of the molecule. Since the degree of hybridization of the two nitrogen atoms can be independently modulated, a fact also supported by crystallographic studies (Norrestam et al, 1969;Werner & Rdnnquist, 1970; Leijonmarck & Werner, 1971; Norrestam & Von Glehn, 1972), the term "folding angle of the flavin molecule" should be avoided. In fact, the degree of hybridization of the nitrogen atoms describes the structure of the reduced flavin molecule more accurately than the angle of folding.…”

Section: Resultsmentioning

confidence: 99%

Reinvestigation of the structure of oxidized and reduced flavin: carbon-13 and nitrogen-15 nuclear magnetic resonance study

Moonen¹,

Vervoort²,

Müller³

1984

Biochemistry

108

116

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Several chemically substituted flavins are investigated in the oxidized and the reduced state by 13C and 15N NMR techniques. The dependence on the polarity of the solvent and on the concentration is studied. In combination with already published results, a semiempirical theory is developed to interpret the chemical shifts in terms of the solution structure of flavins. Where possible, the results are compared with crystallographic and light absorption data. In contrast to common ideas, the solution structure of the oxidized state is not fully coplanar, but the N(10) atom is situated out of plane to a certain degree. Polarizing the flavin by hydrogen bonds in a high dielectric medium moves the N(10) atom into the molecular plane, and the flavin molecule becomes coplanar. In the coplanar molecule, pi electrons are delocalized from the N(10) atom mainly to O(2 alpha) and O(4 alpha). The NMR results show that the solution structure of reduced flavin is mainly governed by sterical hindrance and hydrogen bonds. The findings are in contrast to commonly accepted ideas that reduced flavin is strongly bent. In an apolar solvent, the reduced neutral isoalloxazine is only slightly bent. The formation of hydrogen bonds in a protic solvent of a high dielectric constant decreases the bend. The N(10) atom is now almost fully sp2 hybridized, and the N(5) atom has an endocyclic angle of 115-117 degrees, indicating its predominant sp2 character. The results have several important implications for flavin catalysis.(ABSTRACT TRUNCATED AT 250 WORDS)

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C16h14 - C16h22 (3085 - 3164)

Schudt-Weitz¹,

Strell²

Landolt-Börnstein - Group III Condensed Matter

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Studies on Flavin Derivatives. Crystal Structure of 5-Acetyl-9-bromo-1,3,7,8-tetramethyl-1,5-dihydroalloxazine.

Cited by 12 publications

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NMR Shieldings and Electron Correlation Reveal Remarkable Behavior on the Part of the Flavin N₅ Reactive Center

NMR Shieldings and Electron Correlation Reveal Remarkable Behavior on the Part of the Flavin N₅ Reactive Center

Reinvestigation of the structure of oxidized and reduced flavin: carbon-13 and nitrogen-15 nuclear magnetic resonance study

C16h14 - C16h22 (3085 - 3164)

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Studies on Flavin Derivatives. Crystal Structure of 5-Acetyl-9-bromo-1,3,7,8-tetramethyl-1,5-dihydroalloxazine.

Cited by 12 publications

References 0 publications

NMR Shieldings and Electron Correlation Reveal Remarkable Behavior on the Part of the Flavin N5 Reactive Center

NMR Shieldings and Electron Correlation Reveal Remarkable Behavior on the Part of the Flavin N5 Reactive Center

Reinvestigation of the structure of oxidized and reduced flavin: carbon-13 and nitrogen-15 nuclear magnetic resonance study

C16h14 - C16h22 (3085 - 3164)

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NMR Shieldings and Electron Correlation Reveal Remarkable Behavior on the Part of the Flavin N₅ Reactive Center

NMR Shieldings and Electron Correlation Reveal Remarkable Behavior on the Part of the Flavin N₅ Reactive Center