Stereoselective redn. of 4-demethoxydaunorubicin (I) to give only the single 13-dihydro isomer (II) comprises cultivating a new mutant of the species Streptomyces peucetius subs. aureus (strain 15 87 F.I.), Mycobacterium fortuitum or Croynebacterium mediolanum in presence of (I) under aerobic conditions in an aq. nutrient medium. Pref. cultivation is for 3-8 days at 25-27 esp. 29, deg.C. The new strain M87 F.I. (DSM 2444) is made by treating a parent strain with nitrosoguanidine. (II), described as a new cpd., is an antitumour agent about as actiVe as 4-demethoxydaunorubicin.
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