Compounds having formula (I), wherein R1 is a hydrogen or halogen atom or an alkyl, alcoxy, alkylthio, nitro, hydroxy or cyano radical; R2 is an alkyl radical or a chain -CH(R5)-CO-R6; R3 is (a) a phenyl radical substituted by one or a plurality of substituants selected amongst the radicals -alk-SO3H, -alk-PO3H2, -CH=NOH, -CH=NO-alk-COOX, -S-alk-COOX, -SO-alk-COOX, -SO2-alk-COOX, -CH=CH-COOX, -alk-CO-NHOH, -C(=NOH)-COOX, -alk-N(OH)-CO-alk, -alk-SO2H, -CH=CH-SO3H, -C(COOX)=N-O-alk-COOX, tetrazolylalkyle or a group having the formula (1) or (b) a ring having the formula (A) wherein R9 is a radical =NOX, =NO-alk-COOX, =CH-COOX, -alk-COOX, -alk-SO2H or -alk-SO3H, R10 is an oxygen or sulfur atom or a methylene or alkylimino radical and R11 is a methylene or ethylene radical, R4 is a pyridyle or phenyl radical optionally substituted by one or a plurality of substitutants selected amongst halogen atoms or the alkyl, alcoxy, hydroxy, carboxy, nitro and -CO-NR6 radicals, alk is an alkyl or alkylene radical and X is a hydrogen atom or an alkyl radical. The invention also discloses the salts thereof, their preparation and medicaments containing them.