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Synthesis, EPR, ENDOR and TRIPLE resonance investigations of anthracycline-related semiquinones

✍ Scribed by Hartmut B. Stegmann; Thomas Jülich; Ulrike Höfler; Paul Schuler; Wolfhard Koch; Karsten Krohn; Astrid Eickhoff

Publisher
John Wiley and Sons
Year
1993
Tongue
English
Weight
419 KB
Volume
31
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

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.

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