a subject of the invention is the compounds of formula : in which either r 1 represents h , oh , nh 2 , — m — nr a r b , r a and r b represent h , linear , branched or cyclic alkyl , cycloalkyl -— alkyl , r c , s 2 r c , cr c , s 2 r d or cr d ; or r a and r b with n form an r c radical ; r c represents a saturated , unsaturated or 5 - or 6 - members aromatic ring , containing 1 to 4 heteroatoms chosen from n , o and s , optionally substituted ; r d represents a linear , branched or cyclic alkyl , optionally substituted by 1 to 4 halogens ; or r 1 represents r c or chr e r c or chr e r d ; r e represents h , oh , nh 2 , nh —- alk or n -- alk 2 , or nh —- acyl or nhr c ; r 2 represents h , m — nr a r b , r c , chr e r c or chr e r d , and r ′ 2 represents h ; it being understood that r 1 and r 2 cannot at the same time be h or that r 1 and r 2 or r 2 and r 1 cannot be one m — nr a r b or r c or h and the other one oh , or one h and the other one nh 2 , or one h and the other one m — nr a r b in which r a and r b represent h or alkyl or cr d , in which r d represents an unsubstituted alkyl or cycloalkyl ; or r 1 has the above definition except h and r 2 and r ′ 2 together represent gem dialkyl or alkyl - oxime , or r 2 and r ′ 2 represent respectively r c or r d and oh , nh 2 , nhr c or nhr f , r f being a acyl radical ; or r 1 represents h and r 2 and r ′ 2 together represent alkyl - oxime or one represents r c and the other one represents oh , nh 2 , nhr c or nhr f ; n is 0 or 1 ; r 3 and r ′ 3 represent h or alkyl optionally substituted by 1 to 3 halogens or r 3 represents alkoxy carbonyl and r ′ 3 represents h ; r4 represents methyl optionally substituted by halogen ; r 5 represents h , alkyl or arylalkyl ; r 6 represents h , fluorine , no 2 , cf 3 or cn ; in the form of enantiomers or mixtures , as well as their salts with acids and bases ; their preparation and their application as anti - bacterials , in both human and veterinary medicine .