Oxazolinodaunorubicin, a new daunorubicin derivative with a modified daunosamine moiety, was synthesized. The biological properties of this derivative and the parent daunorubicin were compared. The results showed antiproliferative activity of the derivative with significantly lower toxicity (an LD(50) value ca. 20 times higher than that of parent daunorubicin) and an ability to completely overcome the resistance of cancer cells to this drug in vitro. Cardiotoxicity determination using male mice treated with a single dose of 75% of the LD(50) value indicated that the cardiotoxicity of new analog was much lower than that of the parent drug. Preliminary results in transplanted murine tumor models revealed that a single-dose injection of the tested compounds exhibited antitumor activity in P388 and L1210 leukemia and 16/C mammary adenocarcinoma bearing mice.