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Derivatives of the angucycline urdamycin A (1) were prepared in order to study structure-activity relationships in this group of antitumor antibiotics. Derivatives of 1 formed by methanolysis, O-acylation, hydrogenation and treatment with diazomethane were isolated and characterized by their spectroscopic data. Urdamycin G (20) was isolated from Streptomyces fradiae by shortening the fermentation time. The different glycosidation pattern of the aglycone 14 did not lead to significant differences in the biological activity. O-Acylation was shown to enhance the in vitro activity of 1 against stem cells of murine L1210 leukemia depending on the lipophilicity of the molecules. The importance of the 5,6-double bond of 1 with regard to the antitumor activities is discussed.

Urdamycins, new angucycline antibiotics from Streptomyces fradiae. V. Derivatives of urdamycin A.