The invention is concerned with compounds of general formula (I), wherein R1 signifies lower-alkoxy, R2 signifies hydroxy or lower-alkoxy, R3 signifies hydrogen, cyano, alkyl, alkenyl, cycloalkyl, aryl, heterocycyl, aralkyl, aryl-Q-alkyl, heterocyclalkyl or a group of the formula -(CH¿2?)n-, Q signifies -SO-; R?4, R4'? each independently signify hydrogen, alkyl, aryl or heterocyclalkyl, R?5¿ signifies hydrogen, alkyl, alkoxy, aryl or heterocycyl, or R?4 and R5¿ together can form a group -(CH¿2?)n-, and n is a whole number of 2 to 5, as well as pharmaceutically usable salts thereof; the use of these compounds and their salts as therapeutically active substances; medicaments based on these substances and their production; the use of these substances as medicaments and for the production of antibacterially-active medicaments; as well as the manufacture of the compounds of formula (I) and their pharmaceutically acceptable salts and intermediates for their manufacture.