Urdamycins, new angucycline antibiotics from streptomyces fradiae. VI. Structure elucidation and biosynthetic investigations on urdamycin H

A new angucycline antibiotic has been discovered as a small side product of Streptomyces fradiae (strain Tü 2717), the producer of the urdamycin complex, during screening for biosynthetic relatives of urdamycins C and D. The structure was elucidated after isolation, via strain selection, of a mutant of S. fradiae that produces this new congener in larger amounts. The structure includes a new chromophore containing aglycone that has not been found before among the angucyclines nor as a natural product generally. In urdamycin H (1) the angucycline four-ring system is enlarged by a (p-OH-phenyl)furan moiety and is closely related to urdamycin C (2). The structure was elucidated by comparison of the physico-chemical data with those of known urdamycins, especially with those of urdamycin C (2), and was confirmed by intensive 2D NMR analysis. Biosynthetic studies showed that tyrosine and not the smaller p-OH-phenylglycine is the precursor of the (p-OH-phenyl)furan moiety.