Metabolic products of microorganisms. 240 urdamycins, new angucycline antibiotics from streptomyces fradiae: II. Structural studies of urdamycins B to F

The structures of the angucycline antibiotics urdamycin B (5), E (2) and F (9) were established by comparing of their spectra with those of urdamycin A (1). The structures of urdamycins C and D, the largest compounds of this series, are still incomplete (10 and 11). The aglycones urdamycinone C, D and E can be liberated by methanolysis of the corresponding urdamycins. The liberation of urdamycinone B (6) requires an alcohol-free medium, to prevent its rearrangement to the naphthacenequinone 7 or 8. The urdamycins differ from other 0-glycoside series in their variety of aglycones.