Anthracyclines with the Skeleton of Dihydroxyanthraquinones

Dihydroxylated anthracycUnes can be classified into six groups, with hydroxyls in 1,4, 1,6, 1,11, 4,6 (aklavinones), 4,11 (citromycinones), and 6,11 positions. Only two compoimds have been reported possessing 1,4-dihydroxy groups rhodirubin G (Fo 7) and ruticulomycin B (Fo 8) the only 1,11-dihydroxylated quinone (Fo 18) has to be further confirmed. 

The isomerization of quinocycline B (26a) to isoquinomycin B (2 -epi-26a) starts with the protonation of the heterocycle, followed by ring opening of the pyrrolopyrrole moiety, rotation, and recyclization [34]. 

Celastramycin B (22a) has been isolated together with celastramycin A (which is a halogenated acylpyrrole, and not an anthracycline) from endophytic Streptomyces setonii and S. sampsonii growing on wood of different Celastraceae plants [41]. It was the only halogen-containing anthracycline  

A single diquinone, BE-45985X (28), has been isolated previously from nature [42]. Diquinones usually have a higher oxidation potential than simple quinones, so that rapid reduction by substrate components occurs. The stability, especially in the case of 27b, is certainly due to the sulfur substituent, which lowers the oxidation potential. The new celastramycins exhibited moderate antibacterial activity against Escherichia coli. Staphylococcus aureus, and Bacillus subtilis. 

Only ten compounds have been described in the Uterature as belonging to the group of 4,11-dihydroxylated anthracyclines (citromycinones). The general feature here is the presence of a hydroxy group instead of a carbomethoxy substituent in the 10-position. 

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