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Synthesis, EPR, ENDOR and TRIPLE resonance investigations of anthracycline‐related semiquinones
Author(s) -
Stegmann Hartmut B.,
Jülich Thomas,
Höfler Ulrike,
Schuler Paul,
Koch Wolfhard,
Krohn Karsten,
Eickhoff Astrid
Publication year - 1993
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260310510
Subject(s) - chemistry , electron paramagnetic resonance , moiety , conformational isomerism , anthraquinone , radical , quinone , photochemistry , nuclear magnetic resonance spectroscopy , stereochemistry , crystallography , nuclear magnetic resonance , organic chemistry , molecule , physics
The synthesis of five substituted anthraquinones related to anthracyclines is described. One‐electron reduction of these compounds yields the corresponding semiquinones, which were characterized by EPR, ENDOR and TRIPLE resonance spectroscopy. The data indicate a rapid conformational interconversion of the cyclohexene moiety (ring A in the anthracyclines). The low‐temperature structures could be assigned to half‐chair conformers whose splitting constants and torsion angles were obtained by simple calculations. Introduction of substituents in the 4‐position, disturbing the symmetry of the anthraquinone, results in remarkable changes in the spin density distribution, in contrast to published results. A reinterpretation and assignment of known anthraquinone radicals is presented.