Daunorubicin derivatives

A daunorubicin derivative of the formula ##STR8## wherein R.sub.1 represents a group of the formula ##STR9## in which (i) X.sub.1 and X.sub.2 both represent oxygen or both represent sulphur and the symbols R.sub.3 each represent alkyl of 1 through 4 carbon atoms, phenyl or phenyl-substituted in the para-position by methyl, methoxy or methylthio, or together form an alkylene radical of 2 through 4 carbon atoms, or (ii) one of X.sub.1 and X.sub.2 represents oxygen and the other represents sulphur and the symbols R.sub.3 together form an alkylene radical of 2 through 4 carbon atoms, and R.sub.4 represents hydrogen, alkyl of 1 through 4 carbon atoms or phenyl, and R.sub.2 represents hydrogen or trifluoroacetyl, or a non-toxic pharmaceutically acceptable acid addition salt of said derivative in which R.sub.2 represents hydrogen.