Novel derivatives of fortimicin B and process for preparing same

4,2'-di-N-substituted derivatives of fortimicin B, represented by the formula:

• ##STR27## wherein R.sub.1 represents a ##STR28## or -CH.sub.2 -R.sub.3 group, and R.sub.2 represents a ##STR29## or --CH.sub.2 --R.sub.4 group and wherein R.sub.4 represents an aminoalkyl group having 1 to 8 carbon atoms, hydroxyalkyl group having 1 to 8 carbon atoms, carbamoylaminoalkyl group having 2 to 9 carbon atoms or .omega.-aminohydroxyalkyl group having 2 to 9 carbon atoms wherein the amino group and hydroxy group are bonded to different carbon atoms, and R.sub.3 represents a carbamoylaminoalkyl group having 2 to 9 carbon atoms, and the pharmaceutically acceptable non-toxic acid addition salts thereof.