The present invention provides 2-deoxy-3-O-demethyl-fortimcins A and B and the 4-N-acyl and alkyl derivatives thereof, represented by the formula: ##STR1## wherein R is selected from the group consisting of hydrogen, acyl, aminoacyl,diaminoacyl,N-monoloweralkylaminoalkyl,N,N-diloweralkylaminoalkyl, hydroxy-substituted aminoacyl,loweralkyl, aminoloweralkyl, N-monoloweralkylaminoloweralkyl, N,N-diloweralkylaminoloweralkyl and hydroxy-substituted aminoloweralkyl and the pharmaceutically acceptable salts thereof.